^,^#Aii^ Vl7 A f t M , S V 1 ■ \, m' *' ■ ■ , B' ]i. \; ^■. ,'^?m 'Yl I ■. ■ . 1 ■- 1 ' * ■ \ ■ \ . '■' I l" '\S V > i ' 1 ■ ' V '.l!\'i 5^;'?!V. ' ■ 1 -.A ^ ,•' V > - ■ ( m2 i. M. Bill ^Xtbrarg Nortlr (Eamltna S^tnU Hmnerfiilg Gift From The J. M. PicKELL Family QH567 M5 N.C. STATE UNIVERSITY D.H. HILL LIBR^R^ S00278621 Q THIS BOOK IS DUE ON THE DATE INDICATED BELOW AND IS SUB- JECT TO AN OVERDUE FINE AS POSTED AT THE CIRCULATION DESK. NOV - 4 1987 N''>v 1 8 tya? FEB 2 4 1988 ^'UG-^ 1993 \ ? 1993 MAY 2 9 1996 100M/7-85 EVOLUTION AND ITS RELATION TO RELIGIOUS THOUGHT BY JOSEPH LE COI^TE AUTHOR OF "religion AND SCIENCE," ETC. AND PROFESSOR OF GEOLOGY AND NATURAL HISTORY IN THK UNIVERSITY OF CALIFORNIA NEW YORK D. APPLETON AND COMPxYNY 1888 COPYEIGHT, 1888, By D. APPLETON AND COMPANY. PEEFACE. The subject of the following work may be expressed in three questions : What is evolution ? Is it true ? What then ? Surely, there are no questions of the day more burning than these. Much has been written on each of them, addressed to different classes of minds: some to the scientific, some to the popular, and some to the religious and theological ; but nothing has yet ap- peared which covers the whole ground and connects the different parts together. Much, very much has been written, especially on the nature and the evidences, of evolution, but the literature is so voluminous, much of it so fragmentary, and most of it so technical, that even very intelligent persons have still very vague ideas on the subject. I have attempted to give (1) a very con- cise account of w^hat we mean by evolution, (2) an out- line of the evidences of its truth drawn from many differ- ent sources, and (3) its relation to fundamental rehgious beliefs. I have determined, above all, to make a book so small that it may be read through without much ex- pense of time and patience. But the subject is so large that in order to do so it was necessary to sacrifice all but what was most essential, and to forego all redun- iy PREFACE. daDcy (the bane of so-called popular science) even at the risk of baldness and obscurity. Nevertheless, I hope that the first and second parts will be found not only interesting to the intelligent general reader, but even profitable to the special biologist. I have tried to make these parts as untechnical as possible, but I hope not on that account the less scientific. For I am among those who think that it is not necessary to be superficial in order to be popular — that science may be adapted to the intelligent popular mind without ceasing to be science. The third part seems to me still more important just now. There is a deep and widespread belief in the popular mind, and even to some extent in the scientific mind, that there is something exceptional in the doc- trine of evolution as regards its relation to religious thouo-ht and moral conduct. Other scientific theories have required only some modifications of religious con- ceptions, but this utterly destroys the possibility of all religious belief by demonstrating a pui-e materialism. 'Now this, I believe, is a complete misconception. Thinking men are fast coming to see this ; some, in- deed, have mistaken tlie change for a reaction against evolution. It is a reaction not against evolution, but only against its materialistic implication. Evolution is more and more firmly established every year. The tide of conviction is one which knows no ebb. Some clear statement, in brief space, of its true relation to religious thought seems, therefore, very important at this time. Berkeley, Cal., May, 1887. COISTTEI^TS. PAKT I. WRAT IS F VOLUTION? CnAPTER I. ITS SCOPE AND DEFINITION. PAGE A type of evolution — Development of an egg ..... 3 Universality of evolution — Pervades all nature and concerns all de- partments of thought — One half of all science — Illustrated (1) by human body, (2) by solar system, (3) by society, (4) by earth, (5) by organic kingdom — The term evolution usually, but not rightly, confined to this last . 3 Definition of evolution — /. Progressive change — Shown in the animal body, or the Ontogenic series — In the animal scale, or the Taxo- nomic series — In the geological, or Phylogenic series — The three series similar, though not identical 8 //. Change according to certain laivs — Three laws of succession of organic forms .11 (a) Laio of differentiation — Early forms are generalized ; afterwards separated into specialized forms — Illustrated by fishes, by birds — Whole process of differentiation illustrated by growth and branching of a tree . . . . . . • • .11 {b) Laio of progress of the w7lasm, it gradually added cell to cell, tissue to tissue, organ to organ, and function to function ; thus becoming more and more complex in the mutual action of its correlated parts, as it passed successively through the stages of germ, egg, embryo, and infant, to maturity. This ascending series of genetically connected stages is called the embryonic or Ontogenic series.* There is another series the terms of which are coex- istent, and which, therefore, is not in any sense a genetic or development series, but which it is important to men- tion, because to some degree similar to and illustrative of the last. Commencing with the lowest unicelled micro- scopic organisms, and passing up to the animal scale, as it noiv exists, we lind a series of forms similar, though not identical, with the last. Here, again, we find cell added to cell, tissue to tissue, organ to organ, and func- tion to function, the animal body becoming more and more complex in structure, in the mutual action of its correlated parts, and the mutual action with the environ- ment, until we reach the highest complexity of structure and of internal and external relations only in the highest • * Ontos-gennao (individual-making, or genesis of the indi'. idnal). 10 WHAT IS EVOLUTIO:^'? animals. This ascending series may be called the natural history series ; or, the classification or Taxonomic series.'^ The terms of this series are, of course, not genetically connected ; at least, not directly so connected. In what way they are connected, and how the series comes to -be similar to the last, we shall see by-and-by. Finally, there is still a third series, the grandest and most fundamental of all, but only recently recognized, and therefore still imperfectly known. Commencing with the earliest organisms, the very dawn of life, in the very lowest rocks, and passing onward and upward through Eozoic, Palaeozoic, Mesozoic, Cenozoic, to the Psychozoic or present time, we again find first the lowest forms, and then successivelv forms more and more com- plex in structure, in the interaction of correlated parts and in interaction with the environment, until we reach the most complex internal and external relations, and therefore the highest structure only in the present time.f This series we will call the geological or 'pliylofjenic se- ries. | According to the evolution theory, the terms of this series also are genetically connected. It is, there- fore, an evolution series. Furthermore, it is the most fundamental of the three series, because it is the cause of the other two. The Ontogenic series is like it because it is a brief recapitulation, through heredity, as it were from memory, of its main points. The Taxonomic series * Taxis, nomos (relating to science of arrangement). f This statement is general ; it will be modified hereafter. X Phuh-gennao (kind-making) ; genesis of the race. ITS SCOPE AND DEFINITION. H is like it because the rate of advance along different lines was different in every degree, and therefore every stage of the advance is still represented in a general way among existing forms. Some of these points will be ex- plained more fully in future chapters, in connection with the evidences of the truth of evolution. It will be admitted, then, that we find iwogressive chmige in organic forms throughout geological times. This is the first point in the definition of evolution. II. Change according to Certain Laws. — We have shown continuously progressive change in organic forms during the whole geologic history of the earth, similar in a general way to that observed in embryonic develop- ment. AYe wish now to show that the laivs of change are similar in the two cases. What, then, are the laws of succession of organic forms in geologic times ? I have been accustomed to formulate them thus : a. The law of differentiation ; h. The law of progress of the whole ; c. The law of cyclical movement.* We will take up these and explain them successively, and then, afterward, show that they are also the laws of embryonic development, and therefore the laws of evolution. a. Law of Differentiation. — It is a most significant fact, to Tvhich attention was first strongly directed by Louis Agassiz, that the earliest representatives of any group, whether class, order, or family, were not what we * This formulation of the laws of organic succession was given by me in 1860, before I knew anything of either Darwin's or Spencer's evolu- tion. They were ray own mode of formulating Agassiz's views. 12 WHAT IS EVOLUTION? would now call typical representatives of that group ; but, on the contrary, they were, in a wonderful degree, connecting links ; that is, that along with their distinc- tive classic, ordinal, or family characters they possessed also other characters which connected them closelv with other classes, orders, or families, now widely distinct, without connecting links or intermediate forms. For example : The earliest vertebrates were fishes, but not typical fishes. On the contrary, they were fishes so closely connected by many characters with amphibian reptiles, that we hardly know whether to call some of them reptilian fishes, or fish-like reptiles. From these, as from a common vertebrate stem, were afterward sepa- rated, by slow changes from generation to generation, in two directions, the typical fishes and the true reptiles. So, also, to take another example, the first birds were far different from typical birds as we now know them. Thej were^ on contrary, birds so reptilian in character, that there is still some doubt whether bird-characters or rep- tilian characters predominate in the mixture, and there- fore whether they ought to be called reptilian birds or bird-like reptiles. From this common stem, the more specialized modern reptiles branched off in one direction and typical birds in another, and intermediate forms be- came extinct ; until noio, the two classes stand widely apart, without apparent genetic connection. This sub- ject will be more fully treated hereafter, and other ex- amples given. These two will be sufficient now to make the idea clear. ITS SCOPE AND DEFINITION. 13 Such early forms combining the characters of two or more groups, now widely separated, were called by Agas- siz connecting types, comhining types, synthetic types, and sometimes proplietic types ; by Dana, comprelien- sive types ; and by Huxley, generalized types. They are most usually known now as generalized types, and their widely-separated outcomes specialized types. Thus, in general, we may say that the widely-separated groups of the present day, when traced back in geological times, approach one another more and more until they finally unite to form common stems, and these in their turn unite to form a common trunk. From such a common trunk, by successive branching and rebranching, each branch taking a different direction, and all growing wider and wider apart (differentiation), have been gradually generated all the diversified forms which we see at the present day. The last leafy ramifications — flower-bear- ing and fruit-bearing — of this tree of life, are the fauna and flora of the present epoch. The law might be called a law of ramification, of specialization of the parts, and diversification of the whole. h. Law of Progress of the Whole.— Many imagine that progress is the one law of evolution ; in fact, that evolution and progress are coextensive and convertible terms. They imagine that in evolution the movement must be upward and onward in all parts ; that degener- ation is the opposite of evolution. This is far from the truth. There is, doubtless, in evolution, progress to higher and higher planes ; but not along every line, nor 14 WHAT IS EVOLUTION? in every part ; for this would be contrar\' to the law of differentiation. It is only progress of the whole organic kingdom in its entirety. We can best make this clear by an illustration. A growing tree branches and again branches m all directions, some branches going upward some sidewise, and some downward — anywhere, every- wdiere, for light and air ; but the whole tree grows ever taller in its higher branches, larger in the circumference of its outstretching arms, and more diversified in struct- ure. Even so the tree of life, by the law of differentia- tion, branches and rebranches continually in all direc- tions — some branches going upward to higher planes (progress), some pushing horizontally, neither rising nor sinking, but only going farther from the general- ized origin (specialization) ; some going downward (de- generation), anywhere, everywhere, for an unoccupied place in the economy of j^ature, but the whole tree grows ever higher in its highest parts, grander in its proportions, and more complexly diversified in its structure. It may be well to pause here a moment to show how this mistaken identification of evolution with progress alone, without modification by the more fundamental laws of differentiation, has given rise to misconceptions ill the popular and even in the scientific mind. The bi- ologist is continually met with the question, '^Do you mean to say that any one of the invertebrates, such, for instance, as a spider, may eventually, in the course of successive generations, become a vertebrate, or that a dog ITS SCOPE AND DEFINITION. 15 or a monkey is on the highway to become a man ? " By no means. There is but one straight and narrow way to the highest in evolution as in all else, and few there be that have found it — in fact, probably two or three oYily at every stejp. The animals mentioned above have di- verged from that way. In their ancestral history, they have missed the golden opportunity, if they ever had it. It is easy to go on in the way they have chosen, but impossible to get back on the ascending trunk- line. To compare again with the growing tree, only one straight trunk-line leads upward to the terminal bud. A branch once separated must grow its own way, if it grow at all. Of the same nature is the mistake of some extreme evolutionists, such as Dr. Bastian and Professor Haeckel, and of nearly all anti-evolutionists, viz., that of imagin- ing that the truth of evolution and that of spontaneous generation must stand or fall together. On the con- trary, if life did once arise spontaneously from any lower forces, physical or chemical, by natural process, the con- ditions necessary for so extraordinary a change could hardly ie expected to occur lut once in the history of the earth. They are, therefore, noiu, not only unreproduci- ble, but unimaginable. Such golden opportunities do not recur. Evolution goes only onward. Therefore, the impossibility of the derivation of life from non-life now, is no more an argument against such a derivation oiice, than is the hopelessness of a worm ever becoming a ver- tebrate now, an argument against the derivative origin 16 WHAT IS EVOLUTION? of vertebrates. Doubtless if life were now extinguished from the face of the earthy, it could not again be rekin- dled by any natural process known to us ; but the same is probably true of every step of evolution. If any class — for example, mammals — were now destroyed, it could not be re-formed from any other class now living. It would be necessary to go back to the time and conditions of the separation of this class from the reptilian stem. There- fore, the falseness of the doctrine of abiogenesis,* so far from being any argument against evolution, is exactly what a true conception of evolution and knowledge of its laws would lead us to expect. c. Law of Cyclical Movement. — The movement of evo- lution has ever been onward and upward, it is true, but not at uniform rate in the whole, and especially in the parts. On the contrar}^, it has jDlainly moved in succes- sive cycles. The tide of evolution rose ever higher and higher, without ebb, but it nevertheless came in succes- sive waves, each higher than the preceding and overborne by the succeeding. These successive cycles are the dy- nasties or reigns of Agassiz, and ages of Dana ; the reign of mollusks, the reign of fishes, of reptiles, of mammals, and finally of man. During the early Palaeozoic times (Cambrian and Silurian) there were na vertebrates, f But never in the history of the earth were mollusks of greater size, number, and variety of form than then. * Genesis without previous life — spontaneou's generation, f Fishes were first introduced in the later Siliirian ; but became dominant in the Devonian. ITS SCOPE AND DEFINITION. 17 They were truly the rulers of these early seas. In the absence of competition of still higher animals, they had things all their own way, and therefore grew into a great monopoly of power. In the later Palaeozoic (Devonian) fishes were introduced. They increased rapidly in size, number, and yariety ; and being of higher organization they quickly usurped the empire of the seas, while the mollusca dwindled in size and importance, and sought safety in a less conspicuous position. In the Mesozoic times, reptiles, introduced a little earlier,* finding con- genial conditions and an unoccupied place above, rapidly increased in number, variety, and size, until sea and land seem to have swarmed with them. Never before or since have reptiles existed in such numbers, in such variety of form, or assumed such huge proportions ; nor have they ever since been so highly organized as then. They quickly became rulers in every realm of Nature — rulers of the sea, swimming reptiles ; rulers of the land, walking reptiles ; and rulers of the air, flying reptiles. In the un- equal contest, fishes therefore sought safety in subordina- tion. Meanwhile mammals were introduced in the Meso- zoic, but small in size, low in type (marsupials), and by no means able to contest the empire with the great rep- tiles. But in the Cenozoic (Tertiary) the conditions ap- parently becoming favorable for their development, they rapidly increased in number, size, variety, and grade of organization, and quickly overpowered the great reptiles, * Amphibians were introduced in the Carboniferous, but true reptile not until the Permian. 18 WHAT IS EVOLUTION? which ahiiost immediately sank into the subordinate po- sition in which wt now find them, and thus found com- parative safety. Finally, in the Quaternary, appeared man, contending doubtfully for a while, with the great mammals, but soon (in Psychozoic) acquiring mastery through superior intelligence. The huge and dangerous mammals were destroyed and are still being destroyed ; the useful animals and plants were preserved and made subservient to his wants; and all things on the face of the earth are being readjusted to the requirements of his rule. In all cases it will be observed that the rulers were such because, by reason of strength, organization, and in- telligence, they were fittest to rule. There is alw^ays room at the top. To illustrate again by a growing tree : This successive culmination of higher and higher classes may be comj^ared to the flowering and fruiting of successively higher and higher branches. Each up2:)ermost branch, under the genial heat and light of direct sunshine, re- ceived in abundance by reason of position, grew rapidly, flowered, and fruited ; but quickly dwindled when over- shadowed by still higher branches, which, in their turn, monopolized for a time the precious sunshine. But observe, furthermore : when each ruling class de- clined in importance, it did not perish, but continued in a subordinate position. Thus, the whole organic king- dom became not only higher and higher in its highest forms, but also more and more complex in its structure and in the interaction of its correlated parts. The whole process and its result is roughly represented in the ac- ITS SCOPE AND DEFINITION. 19 Silurian Devon, and Curb. Mesozoic. Fig. 1. Tert'y and Quat. Present. companjing diagram, Fig. 1, in which A B represents the course of geological time and the curve, the rise, culmination, and decline of successive dominant classes. The Above Three Laws are Laws of Evolutioi^^. These three laws we have shown are distinctly recog- nizable in the succession of organic forms in the geologi- cal history of the earth. They are, therefore, tindoubt- edly the general laivs of succession. Are they also laws of evolution ? Are they also discoverable in embryonic development, the t^'pe of evolution ? They are, as we now proceed to show : Differentiation. — In reproduction the new individual appears : 1. As a germ-ccW — a single microscopic living cell. 3. Then, by growth and multiplication of cells, it becomes an egg. This may be characterized as an aggre- gate of similar cells, and therefore is not yet differen- tiated into tissues and organs. In other words, iX is not yet visibly organized ; for organization may be defined as the possession of different parts, performing different functions, and all co-operating for one givoii end, viz., the life and well-being of the organism. 8. Then com- mences the really characteristic process of development, 20 WHAT IS EVOLUTION? viz., differentiation or diversification. The cells are at first all alike iu form and function, for all are globular in form, and each performs all the functions necessary for life. From this common point now commences de- velopment in differe7it directions, which may be com- pared to a branching and rebranching, with more and more complex results, according as the animal is higher in the scale of organization and advances toward a state of maturity. First, the cell-aggregate {<^gg) separates into three distinct layers of cells, called ecto-blast, en do-blast, and meso-blast. These by further differentiation form the three fundamental groups of organs and functions, viz., the nervous system, the nutritive system, and the Mood system : the first presiding over the exchange of force or influence, by action and reaction with the environment, and between the different parts of the organism ; the sec- ond presiding over the exchange of matter with the envi- ronment, by absorption and elimination ; the third presid- ing over exchanges of matter between different parts of the organism. The first system of functions and organs may be compared to a S3'stem of telegraphy, foreign and domestic ; the second to foreign commerce ; the third to an internal carrying-trade. Following out any one of these groups in higher animals, say the nervous system, it quickly differentiates again into two sub-S3^stems, viz., cer- ebro-spinal and ganglionic, each having its own distinctive functions, which we can not stoj? to explain. Then the cerebro-spinal again differentiates into voluntary and re- flex systems. All of these have meanwhile separated into ITS SCOPE AND DEFINITION. 21 sensory and motor centers and fibers. Then, taking only the sensory fibers, these again are differentiated into five special senses, each having a wholly difi;erent function. Then, finally, taking any one of these, say the seiise of touch or feeling, this again is differentiated into many kinds of fibers, each responding to a different impression, some to heat, others to cold, still others to pressure, etc. We have taken the nervous svstem : but the same differ- entiation and redifferentiation takes place in all other systems, and is carried to higher and higher points ac- cording to the position in the scale of the animal which is to be formed. Or, to vary the mode of presentation a little, the cells of the original aggregate, commencing all alike, imme- diately begin to take on different forms, in order to per- form different functions. Some cells take on a certain form and aggregate themselves to form a peculiar tissue which we call muscle, and which does nothing else, can do nothing else, than contract under stimulus. Another group of cells take on another peculiar form and aggre- gate themselves to form another and very different tis- sue, viz., nervous tissue, which does nothing and can do nothing but carry influence back and forth between the great external world and the little world of consciousness within. Still another group of cells take still another forai and aggregate to form still another tissue, viz., the ep^tlielial, whose only function is to absorb nutritive and eliminate waste matters. Thus, by differentiation of form and limitation of function, or division of labor, the 22 WHAT IS EVOLUTION? different parts of the organism are bound more and more closely together by mutnal dependence, and the whole becomes more and more distinctly individuated, and separation of parts becomes more and more a mutilation, and finally becomes impossible without death. This pro- cess, as already said, reaches its highest point only in the later stages of deyelopment of the highest animals. Progress. — The law of progress is, of course, admitted to be a law of ontogeny ; but observe here, also, it is true only of the whole and not necessarily of all the j^arts, ex- cept from the point of view of the ichole. Thus, for ex- ample, starting all from a comnmn form or generalized type, some cells advance to the dignity of brain-cells, whose function is somehow connected with the genera- tion or at least the manifestation of thought, will, and emotion ; other cells descend to the position of kidney- cells, whose sole function is the excretion of urine. But here, also, the highest cells are successively higher, and the whole aggregate is successively nobler and more com- plex. It is again a branching and rebranching, in ev- ery direction, some going upward, some downward, some horizontally, anywhere, everywhere, to increase the com- plexity of relations internal and external, and therefore to elevate the plane of the whole. Cyclical Movement.— Lastly, the law of cyclical move- ment is also a law of ontogeny and therefore of evolution. This law, however, is less fundamental than the other two, and is, therefore, less conspicuous in the ontogenic than in the i>hylogenic series. It is conspicuou'S only in ITS SCOPE AND DEFINITION". 23 the later stages of ontogeny, and in other higher kinds of evolution, such as social evolution. For example, in the ontogenic development of the body and mind from childhood to manhood we have plainly successive culmi- nations and declines of higher and higher functions. In bodily development we have culminating first the nutri- tive functions, then the reproductive and muscular, and last the ceredral. In mental development we have cul- mination first of the receptive and retentive faculties in childhood, then of imaginative and aesthetic faculties in youth and young manhood ; then of the reflective and elaborative faculties — the faculties of productive work in mature manhood ; and, finally, the moral and religious sentiments in old age. The first gathers and stores ma- terials ; the second vivifies and makes them plastic building materials ; the third uses them in actual con- structive work — in building the temple of science and philosophy ; and the fourth dedicates that temple only to noblest purposes. Observe here, also, that when each group of faculties culminates and declines, it does not perish, but only be- comes subordinate to the next higher dominant group, and the whole psychical organism becomes not only higher and higher in its highest j^arts, but also more and more complex in its structure and in the interaction of its correlated parts. Observe, again, the necessity laid upon us by this law — the necessity of continued evolution to the end. Child- hood, beautiful childhood, can not remain — it must 24 WHAT IS EVOLUTIO^^? quickly pass. If, with the decline of its characteristic faculties, the next higher group characteristic of youth do not increase and become dominant, then the glory of life is already past and deterioration begins. Have we not all seen sad examples of this ? Youth, glorious youth, must also pass. If the next higher group of re- flective and elaborative faculties do not arise and domi- nate, then progressive deterioration of character com- mences here — thenceforward the whole nature becomes coarse, as we so often see in young men, or else shrivels and withers, as we so often see in young women, final- ly, manhood, strong and self-relying manhood, must also pass. If the moral and religious sentiments have not been slowly growing and gathering strength all. along, and do not now assert their dominance over the whole man, then commences the final and saddest decline of all, and old age becomes the pitiable thing we so often see it. But, if the evolution have been normal through- out ; if the highest moral and religious nature have been gathering strength through all, and now dominates all, then the psychic evolution rises to the end — then the course of life is like a wave rising and cresting only at the moment of its dissolution, or, like the course of the sun, if not brightest at least most glorious in its setting. And thus — may we not hope ?— the glories of the close of a well-spent life become the pledge and harbinger of an eternal to-morrow ? We have thus far illustrated the three laws of succes- sion of organic forms by ontogen}', because this is the ITS SCOPE AND DEFINITION. 25 type of eyolution ; but they may be illustrated also bv other forms of evolution. Next to the development of the individual, undoubtedly the progress of society fur- nishes the best illustration of these laws. Commencing with a condition in which each indi- vidual performs all necessary social functions, but very imperfectly ; in which each individual is his own shoe- maker and tailor, and house-builder and farmer, and therefore all persons are socially alike ; as society ad- vances, the constituent members begin to diverge, some taking on one social function and some another, until in the highest stages of social organization this diversifica- tion or division and subdivision of labor reaches its high- est point, and each member of the aggregate can do per- fectly but one thing. Thus, the social organism becomes more and more strongly bound together by mutual de- pendence, and separation becomes mutilation. I do not mean to say that this extreme is desirable, but only that an approach to this is a natural law of social develop- ment. Is not this the laiu of differentiation? So also progress is here, as in other forms of evo- lution — a progress of the ivhole, but not necessarily of every part. Some members of the social aggregate ad- vance upiuard to the dignity of statesmen, philosophers, and poets ; some advance doivnward to the position of scavengers and sewer-cleansers."^ But the highest mem- bers are progressively higher, and the whole aggregate is * Of coui^ I mean downward in social function. Individually the scavenger may be nobler than the statesman. 26 WHAT IS EVOLUTION? progressively grander and more complex in structure and functions. So, again, the laiu of cyclical movement is equally conspicuous here. Society everywhere advances, not uni- formly, but by successive waves, each higher than the last ; each urged by a new and higher social force, and embodying a new and higher phase of civilization. Again : as each phase declines, its characteristic social force is not lost, but becomes incorporated into the next higher phase as a subordinate j)i'iiiciple, and thus the social organism as a whole becomes not only higher and higher, but also more and more complex in the mutual relations of its interacting social forces. Let us not be misunderstood, however. There is un- doubtedly in social evolution something more and higher than we have described, but which does not concern us here, except to guard against misconstruction. There is in society a voluntary progress wholly different from the evolution we have been describing. In true or ma- terial evolution natural law works for the betterment of the whole utterly regardless of the elevation of the indi- vidual, and the individual contributes to the advance of the whole quite unconsciously while striving only for his own betterment. This unconscious evolution by natural law inherited from the animal kingdom is conspicuous enough in society, especially in its early stages, but we would make a great mistake if we imagined, as some do, that this is all. Besides the unconscious evolution by natural laws, inlierited from below, there is a higher evo- ITS SCOPE A^-D DEFINITION". 2T lution, inherited from above, indissolubl}^ connected with man's spiritual nature — a conscious, yoluntary strivino- of the best members of the social aggregate for the bet- terment of the whole — a conscious, Toluntary striving both of the individual and of society toward a recog- nized ideal. In the one kind of evolution the fittest are those most in harmony with the environment, and which therefore always survive ; in the other, the fittest are those most in harmony with the ideal, and which often do not survive. The laws of this free voluntary progress are little understood. They are of supreme importance, but do not specially concern us here. We will speak of it again in another chapter. The three laws above mentioned might be illustrated equally well by all other forms of evolution. We have selected only those which are most familiar. They may, therefore, be truly called the laws of evolution. We have shown that they are the laws of succession of or- ganic forms. III. Change by Means of Resident Forces.— Thus far in our argument I suppose that most well-informed men will raise no objection. It will be admitted, I think, even by those most bitterly opposed to the theory of evo- lution, that there has been throughout the whole geologi- cal history of the earth an onward movement of the or- ganic kingdom to higher and higher levels. It will be admitted, also, that there is a grand and most significant resemblance between the course of development of the organic kingdom and the course of embryonic develop- 28 WHAT IS EYOLUTION^? ment — between the laws of succession of organic forms and the laws of ontogenic evolution. But there is an- other essential element in ontogenic evolution. It is that the forces or causes of evolution are natural ; that they reside in the thing developing and in the reacting environment. This we know is true of embryonic devel- opment ; is it true also of the geologic succession of or- ganic forms ? It IS true of ontogeny ; is it true also of phylogeny ? If not, then only by a metaphor can we call the process of change in the organic kingdom throughout geological history an evolution. This is the point of discussion, and not only of discussion, but, alas ! of heated and even angry dispute. The field of discussion is thus narrowed to this third point only. Before stating the two opposite views of the cause of evolution, it is necessary to remind tlie reader that when the evolutionist speaks of the forces that determine pro- gressive changes in organic forms as resident or inherent, all that he means, or ought to mean, is that they are resident in the same sense as all natural forces are resi- dent ; in the same sense that the vital forces of the em- bryo are resident in the embryo, or that the forces of the development of the solar system according to the nebular or any other cosmogonic hypotheses are resident in that system. In other words, they mean only that they are natural, not supernatural. This does not, of course, touch that deeper, that deepest of all questions, viz., the essential nature and origin of natural forces ; how far they are independent and self-existent, and how far ITS SCOPE AND DEFINITION. 29 they are only modes of divine energy. This is a question of philosophy, not of science. This question is briefly discussed in another place (Part III, Chap. Ill) ; it does not immediately concern us here. The Two Views briefly Contrasted.— As already stated, all will admit a grand resemblance between the stages of embryonic development and those of the development of the organic kingdom. This was first brought out clearly by Louis Agassiz, and is, in fact, the greatest result of his life-work. All admit, also, that the embryonic de- velopment is a natural process. Is the development of the organic kingdom also a natural process ? All biolo- gists of the present day contend that it is ; all the old- school naturalists, with Agassiz at their head, and all anti-evolutionists of every school, contend that it is not. We take Agassiz as the type of this school, because he has most fully elaborated and most distinctly formulated this view. As formulated by him, it has stood in the minds of many as an alternative and substitute for evo- lution. According to the evolutionists, all organic forms, "whether species, genera, families, orders, classes, etc., are variable, and, if external conditions favor, these varia- tions accumulate in one direction and gradually produce new forms, the intermediate links being usually destroyed or dying out. According to Agassiz, the higher groups, such as genera, families, orders, etc., are indeed vari- able by the introduction of new species, but sjDecics are the ultimate elements of classification, and, like the ul- 30 WHAT IS EVOLUTION"? timate elements of chemistry, are unchangeable ; and, therefore, the speculations of the evolutionist concerning the transmutation of species are as vain as were the spec- ulations of the alchemists concerning the transmutation of metals — that the origin of man, for example, from any lower sj^ecies is as impossible as the origin of gold from any baser metal. Both sides admit frequent change of species during geological history, but one regards the change as a change by gradual transmutation of one species into another through successive generations and by natural process, the other as change by substitution of one species /or another by direct supernatural creative act. Both admit the gradual development of the organic kingdom as a whole through stages similar to those of embryonic development ; but the one regards the whole process as natural, and therefore strictly comparable to embryonic development, the other as requiring frequent special interference of creative energy, and therefore comparable rather to the development of a building un- der the hand and according to the preconceived plan of an architect — a plan, in this case, conceived in eternity and carried out consistently through infinite time. It is seen that the essential point of difference is this : The one asserts the variability of species (if conditions favor, and time enough is given) without limit ; the other as- serts the permanency of specific forms, or their variabil- ity only within narrow limits. The one asserts the origin of species by ^'descent with modificatiG7is'''j the other, the origin of species by '^special act of creation.^^ The \/' ITS SCOPE AND DEFINITION. 31 one asserts the law of continuity (i. e., that each stage is the natural outcome of the immediately preceding stage) in this, as in every other department of Nature ; the other asserts that the law of continuity (i. e., of cause and effect) does not hold in this department ; that the links of the chain of changes are discontinuous, the con- nection between them being intellectual, not physical. So much for sharp contrasting characterization of the two "views, necessary for clear understandmg of much that follows. We y/ill have to give them more fully hereafter when we take up the evidences of evolution in Part II. 3 CHAPTER 11. THE BELATIOI^" OF LOUIS AGASSIZ TO THE THEOEY OF EVOLUTIOI^. In" order to clear up the conception of evolution, it is necessary to give a brief history of the idea, and espe- cially to explain the relation of Louis Agassiz to that theory. This is the more necessary, because there is a deep and wide-spread misunderstanding on this subject, and thus scant justice has been done our great naturalist, especially by the English and Germans ; and also because this relation is an admirable illustration of an important principle m scientific philoso23hy. Like all great ideas, we find the first germs of this in Greek philosophy, in the cosmic speculations of Thales and Pythagoras, l^ext (about 100 b. c.) we find it more clearly expressed by the Eoman thinker, Lucretius, in his great philosophic poem entitled "De Eerum Natura." After a dormancy of nearly eighteen centuries it next emerges with still more clearness in the theological specu- lations of Swedenborg and the philosophical speculations of Kant. All these we pass over with bare mention, be- cause these thinkers approached the subject from the RELATION OF AGASSIZ TO EVOLUTION. 33 philosophic rather than the scientific side — in the meta- physical rather than the scientific spirit. The first serious attempt at scientific presentation of the subject was by the celebrated naturalist, Lamarck, in a work entitled ** Philosophic Zoologique," published in 1809. It is not necessary, in this rapid sketch, to give a full account of Lamarck's views. Suffice it to say that the essential idea of evolution, viz., the indefinite vari- ability and the derivative origin of species, was insisted on with great learning and skill, and illustrated by many examples. With Lamarck, the factors of evolution or causes of change of organic forms were — 1. Modification of organs in function and therefore in structure, by a changing environment — external factor ; and, 2. Modifi- cation of organs by use and disuse — internal factor. In both cases the modifications are inherited and increased from generation to generation, without limit. This sec- ond factor seems to have taken, in the mind of Lamarck, the somewhat vague and transcendental form of aspira- tion or upward striving of the animal toward higher conditions. These are acknowledged to-day as true fac- tors of evolution, but the distinctively Darwinian factor, viz., '^divergent variation and natural selection," was not then thought of. The publication of Lamarck's views produced a powerful impression, but only for a little while. Pierced by the shafts of ridicule shot by nimble wits of Paris, and crushed beneath the heavy weight of the authority of Cuvier, the greatest naturalist and comparative anatomist of that or perhaps 34 WHAT IS EVOLUTION? of any time, it fell almost still-born. I believe it was best that it should thus perish. Its birth was prema- ture ; it was not fit to live. The world was not yet pre- pared for a true scientific theory. Nevertheless, the work was not without its effect upon some of the most advanced thinkers of that time ; upon Saint-Hilaire and Comte in France, and upon Goethe and Oken in Ger- many. It was good seed sown and destined to spring up and bear fruit in suitable environment ; but not yet. The next attempt worthy of attention in this rapid sketch is that of Robert Chambers, in a little volume en- titled '^Vestiges of a Natural History of Creation," pub- lished in 1844. It was essentially a reproduction of Lamarck's views in a more popular form. It was not a truly scientific work nor written by a scientific man. It was rather an appeal from the too technical court of sci- ence to the supposed wider and more unprejudiced court of popular intelligence. It was therefore far more elo- quent than accurate ; far more specious than profound. It w^as, indeed, full of false facts and inconsequent rea- sonings. Nevertheless, it produced a very strong impres- sion on the thinking, popular mind. But it also quickly fell, pierced by keen shafts of ridicule, and crushed be- neath the heavy weight of the authority of all the most prominent naturalists of that time, with Agassiz at their head. The question for the time seemed closed. I be- lieve, again, it was best so, for the time was not yet fully ripe. I know full well that many think with Haeckel that RELATION OF AGASSIZ TO EVOLUTION. 35 biology was kept back half a century by the baneful au- thority of Cuyier and Agassiz ; but I can not think so. The hypothesis was contrary to the facts of science as then knoivn and understood. It was conceiyed in the spirit of baseless siDcculation, rather than of cautious induction ; of skillful elaboration rather than of earnest truth-seeking. Its general acceptance would have de- bauched the true spirit of science. I repeat it : the time was not yet ripe for a scientific theory. The ground must first be cleared and a solid foundation built ; an in- superable ohstacle to hearty rational acceptance must first be removed, and an inductive lasis must be laid. The Obstacle removed. — The obstacle in the way of the acceptance of the derivative origin of species was the then prevalent 7iotion concerning the nature of life. We must briefly sketch the change which has taken place in the last forty years in our ideas on this subject. Until about forty years ago, the different forces of Nature, such as gravity, electricity, magnetism, light, heat, chemical affinity, etc., were supposed to be entirely distinct. The realm of Nature was divided up into a number of distinct and independent principalities, each subject to its own sovereign force and ruled by its own petty laws. About that time it began to be evident, and is now universally acknowledged, that all these forces are but different /on7Z5 of one, universal, omnipresent energy, and are transmutable unto one another back and forth without loss. This -is the doctrine of correlation of forces and conservation of energy, one of the grandest 36 WHAT IS EVOLUTION? ideas of modern times. But one force seemed still to be an exception. Life-force was still believed to be a pe- culiar, mysterious principle or entity, standing above other forces and subordinating them ; not correlated with, not transmutable unto, nor derivable from, other and lower forces, and therefore in some sense super- natural. Now, if this be true of li^mg forces, it is per- fectly natural, yea, almost necessary, to believe that liv- ing /orms are wholly different from other forms in their origin. New forms of dead matter may be derived, but new living forms are underived. Other new forms come by natural process, new organic forms by supernatural process. The conclusion was almost unavoidable. But soon vital force also yielded to the general law of correla- tion of natural forces. Vital forces are also transmutable into and derivable from physical and chemical forces. Sun-force, falling on the green leaves of plants, is ab- sorbed and converted into vital force, disappears as light to reappear as life. The amount of life-force generated is measured by the amount of light extinguished. The same is true of animal life. As in the steam-engine the locomotive energy is derived from the fuel consumed and measured by its amount, so in the animal body, the ani- mal heat and animal force are derived from and measured by the food and tissue consumed by combustion. Thus, vital force may be regarded as so much force withdrawn from the general fund of chemical and physical forces, to be again refunded without loss at death. This obstacle is, therefore, now removed. If vital force falls in the RELATION" OF AGASSIZ TO EVOLUTION. 37 same category as other natural forces, there is no reason why living forms should not fall into the same category in this regard as other natural forms. If new forms of dead matter are derived from old forms by modification, according to physical laws, there is no reason why new living forms should not also be derived from old forms by modification according io pliy biological laws. Thus, at last, the obstacle was removed — the ground was cleared. The Basis laid. — But Science is not content with re- moval of a priori objections. She must also have posi- tive proofs. The ground must not only be cleared, but a true inductive basis of facts, and especially of laws and methods, must be laid. This was the life-wovh of Agas- siz. Yes, as strange as it may seem to some, it is never- theless true that the whole inductive basis, uj^on which was afterward built the modern theory of evolution, was laid by Agassiz, although he himself persistently refused to build upon it any really scientific superstructure. It is plain, then, that all attempts at building previous to Agassiz's work must, of necessity, have resulted in an unsubstantial structure — an edifice built on sand, which could not and ought not to stand. I must stop here in order to explain somewhat fully this important point, and thus to give due credit to the work of Agassiz. The title of any scientist to greatness must be deter- mined, not so much by the multitude of new facts he has discovered as by the new laws he has established, and especially by the new methods he has inaugurated or per- 38 WHAT IS EVOLUTION? fected, Now, I tliink it can be shown that to Agassiz^, more than to any other man, is due the credit of having established the laws of succession of living forms in the geological history of the earth — laws upon which must rest any true theory of evolution. Also, that to him, more than to any other man, is due the credit of having perfected the method (method of comparison) by the use of which alone biological science has advanced so rapidly in modern times. This is high praise. I wish to justify it. I begin with the method. Scientific methods bear the same relation to intellect- ual progress that tools, instruments, machines, mechani- cal contrivances of all sorts, bear to material progress. They are intellectual contrivances — indirect ways of ac- complishing results far too hard for bare-handed, unaided intellectual strength. As the civilized man has little or no advantage over the savage in bare-handed strength of muscle, and the enormous superiority of the latter in accomplishing material results is due wholly to the use of mechanical contrivances or machines ; even so, in the higher sphere of intellect, the scientist makes no preten- sion to the possession of greater unaided intellectual strength than belongs to the uncultured man, or even perhaps to the savage. The amazing intellectual results achieved by science are due wholly to the use of intellect- ual contrivances or scientific methods. As in the lower sphere of material progress the greatest benefactors of the race are the inventors or perfecters of new mechani- cal contrivances or machines, so also in the higher sphere RELATION OF AGASSIZ TO EVOLUTION. 39 of intellectual progress the greatest benefactors of the race are the inventors or perfecters of new intellectual contrivances or methods of researcJi. To illustrate the power of methods, and the necessity of their use, take the case of the method of notation, so characteristic of mathematics, and take it even in its simplest and most familiar form : Nine numeral figures, having each a value of its own, and another dependent upon its position ; a few letters, a and h, and x and y, connected by symbols, -J- and — and = : that is all. And yet, by the use of this simple contrivance, the dullest school-boy accomplishes intellectual results which would defy the utmost efforts of the unaided strength of the greatest genius. And this is only the simplest tool-form of this method. Think of the results accomplished by the use of the more complex machinery of the higher mathematics ! Take next the method of experiment so characteristic of physics and chemistry. The phenomena of the external world are far too complex and far too much affected by disturbing forces and modifying conditions to be under- stood at once by bare, unaided intellectual insight. They must first be simplified. The physicist, therefore, con- trives artificial phenomena under ideal conditions. He removes one complicating condition after another, one disturbing cause and then another, watching meanwhile the result, until finally the necessary condition and the true cause are discovered. On this method rests the whole fabric of the ph3"sical and chemical sciences. 40 WHAT IS EVOLUTION"? But when we rise still higher, viz.j. into the plane of life, the phenomena of Nature become still more com- plex and difficult to understand directly ; and yet just here, where we are the most powerless without some method, our method of experiment almost wholly fails us. The phenomena of life are not only far more com- plex than those of dead matter, but the conditions of life are so nicely adjusted, the equilibrium of forces so deli- cately balanced, that, when we attempt to introduce our clumsy hands in the way of experiment, we are in danger of overthrowing the equilibrium, of destroying the con- ditions of the experiment, viz., life ; and then the whole problem falls immediately into the domain of chemistry. What shall we do ? In this dilemma we find that Na- ture herself has already prepared for us, ready to hand, an elaborate series of simplified conditions equivalent to experiments. The phenomena of life are, indeed, far too complex to be 'at once understood — the problem of life too hard to be solved — in the higher animals ; but, as we go down the animal scale, complicating conditions are removed one by one, the phenomena of life become sim- pler and simpler, until in the lowest microscopic cell or spherule of living protoplasm we finally reach the sim- plest possible expression of life. The equation of life is reduced to its simplest terms, and now, if ever, we begin to understand the true value of the unknown quantity. This is the natural history series, or Taxonomic series, already spoken of on page 10. Again, Nature has pre- pared, and is now preparing daily before our eyes, an- RELATION OF AGASSIZ TO EVOLUTION. 41 other series of gradually simplified conditions. Com- mencing with the mature condition of one of the higher animals — for example, man — and going backward along the line of individual history through the stages of in- fant embryo, egg and germ, we find again the phenomena of life becoming simpler and simpler, until we again reach the simplest conceivable condition in the single microscopic cell or spherule of living protoplasm. This, as already explained, is the embryonic or Ontogenic se- ries. Again, that there be no excuse for man's ignorance of the laws of life, Nature has prepared still another series ; and this the grandest of all, for it is the cause of both the others. Commencing with the plants and ani- mals of the present epoch, and going back along the track of geological times, through Cenozoic, Mesozoic, Palaeozoic, Eozoic, to the very dawn of life — the first syllable of recorded time — and we find again a series of organic forms growing simpler and simpler, until, if we could find the very first, we would undoubtedly again reach the simplest condition in the lowest con- ceivable forms of life. This, as we have already seen, is the geologic or evolution, or Phylogenic series. We have already explained these three series, only in this connection it suits our purpose to take the terms back- ward. Now, it is by compariso?i of the terms of each of these series going up and down, and watching the first appear- ance, the growth, and the perfecting of tissues, organs, functions, and by the comparison of the three series 42 WHAT. IS EVOLUTION? with one another term by term — I say it is wholly by comparison of this kind that biology has in recent times become a true inductive science. This is the ''method of comiKirison.^^ It is the great method of research in all those departments which can not be readily managed by the method of experiment. It has already regenerated biology, and is now applied with like success in sociology under the name of historic method. Yes ; anatomy be- came scientific only through comparative anatomy, physi- ology through comparative physiology, and embryology through comparative embryology. May we not add, soci- ology will become truly scientific only through compara- tive sociology, and psychology through comparative psy- chology ? Now, while it is true that this method, like all other methods, has been used, from the earliest dawn of thought, in a loose and imperfect way, yet it is only in very recent times that it has been organized, systema- tized, perfected, as a true scientific method, as a great instrument of research ; and the prodigious recent ad- vance of biology is due wholly to this cause. Now, among the great leaders of this modern movement, Agas- siz undoubtedly stands in the very first rank. I must try to make this point plain, for it is by no means gen- erally understood. Cuvier is acknowledged to be the great founder of comparative anatomy. He it was that first perfected the method of comparison, but comparison only in one series — the Taxonomic. Von Baer and Asrassiz added to this, RELATION OF AGASSIZ TO EVOLUTION. 43 comparison in the ontogeni'c series also, and comparison of these two series with each other, and therefore the application of embryology to the classification of animals. If Von Baer was the first announcer, Agassiz was the first great practical worker by this method. Last and most important of all, in its relation to evolution, Agas- siz added comparison in the 'geologic or pJiylogenic series. The one grand idea underlying Agassiz's whole life-work was the essential identity of the three series, and there- fore the light which they must shed on one another. The two guiding and animating principles of his scien- tific work were — 1. That the embryonic development of one of the higher representatives of any group repeated in a general w^ay the terms of the Taxonomic series in the same group, and therefore that embryology furnished the key to a true classification ; and, 2. That the succes- sion of forms and structure in geological times in any group is similar to the succession of forms and struct- ure in the development of the individual in the same group, and thus that embryology furnishes also the key to geological succession. In other words, during his whole life, Agassiz insisted that the laws of embryonic development (ontogeny) are also the law^s of geological succession (phylogeny). Surely this is the foundation, the only solid foundation, of a true theory of evolution. It is true that Agassiz, holding as he did the doctrine of permanency of specific tyj^es, and therefore rejecting the doctrine of the derivative origin of species, did not admit the causal or natural relation of phylogenic succes- 44: WHAT IS EVOLUTION? sion to embryonic succession and taxonomic order as we now believe it — it is true that for him the relation be- tween the three series was an intellectual not a physical one — consisted in the preordained plans of the Creator, and not in an}' genetic connection or inherited property ; but evidently the first and greatest step was the discovery of the relation itself, however accounted for. The rest was sure to follow. But more. Not only did Agassiz establish the essen- tial identity of the geologic and embryonic succession, the general similarity of the two series, phylogenic and ontogenic, but he also announced and enforced all the formal laws of geologic succession (i. e., of evolution), as we now know them. These, as already stated and illus- trated, are the law of differentiation, the law of progress of the whole, and the law of cyclical movement, al- though he did not formulate them in these w^ords. No true inductive evidence of evolution was possible without the knowledge of these laws, and for this knowledge we are mainly indebted to Asfassiz. He well knew also that they were the laws of embryonic develo^Dment and there- fore of evolution ; but he avoided the word evolution, as implying the derivative origin of species, and used in- stead the word development, though it is hard to see in what the words differ. Thus, it is evident that Agassiz laid the whole foundation of evolution, solid and broad, but refused to build any scientific structure on it ; he re- fused to recognize the legitimate, the scientifically neces- sary outcome of his own work. Nevertheless, without his EELATION OF AGASSIZ TO EVOLUTION. 45 work a scientific theory of eyolution would have been impossible. Without Agassiz (or his equivalent), there would have been no Darwin. There is something to us supremely grand in this re- fusal of Agassiz to accept the theory of eyolution. The opportunity to become the leader of modern thought, the foremost man of the century, was in his hands, and he refused, because his religious, or, perhaps better, his philosophic intuitions, forbade. To Agassiz, and, in- deed, to all men of that time, to many, alas ! even now, evolution is materialism. But materialism is Atheism. Will some one say, the genuine Truth-seeker follows where she seems to lead whatever le the consequences'^ Yes ; whatever be the consequences to one's self, to one's opinions, prejudices, theories, philosophies, but not to still more certain truth. Now, to Agassiz, as to all genu- ine thinkers, the existence of God, like our own exist- ence, is more certain than any scientific theory, than any- thing can possibly be made by proof. From his stand- point, therefore, he was right in rejecting evolution as conflicting with still more certain truth. The mistake which he made was in imagining that there was any such conflict at all. But this was the universal mistake of the age. A lesser man would have seen less clearly the higher truth and accepted the lower. A greater man would have risen above the age, and seen that there was no conflict, and so accepted both. All thinking men are coming to this conclusion now, but none had done so then. 46 WHAT IS EVOLUTION? Now, then, at last, the obstacle of supernaturalism in the realm of Nature having been removed by the estab- lishment of the doctrine of correlation of natural forces, and the extension of this doctrine to embrace also life- force ; and now also a broad and firm basis of carefully- observed facts and well-established laws of succession of organic forms having been laid by Agassiz, when again, for the third time, the doctrine of origin of species "by derivation with modifications " was brought forward by Darwin in a far more perfect form, with more abundant illustrative materials, and with a new and most potent factor of modification — viz., divergent variations and natural selection — it found the scientific world already fully prepared, and anxiously waiting. I say anxiously waiting — for the supposed supernatural origin of species had been the one exception to the otherwise universal law of cause and effect, or the law of continuity. It was therefore in open contradiction to the whole drift of scientific thought for five hundred years. Is it any wonder, then, that the derivative origin of species was welcomed with joy by the scientific world ? For five hundred years, scientific thought, like a rising tide which knows no ebb, had tended thitherward with ever- increasing pressure, but kept back by the one supposed fact of the supernatural origin of species. Darwin lifted the gate, and the in-rushing tide flooded the whole do- main of thought. What, then, is the place of Agassiz in biological sci- ence ? What is the relation of Agassiz to Darwin — of KELATION OF AGASSIZ TO EVOLUTIOX. 47 Agassizian development to Darwinian evolution ? I an- swer, it is the relation of formal science to physical or causal science. Agassiz advanced bialogy to the formal stage ; Darwin carried it forward, to some extent at least, to the physical stage. All true inductive sciences in their complete development pass through these two stages. Science in the one stage treats of the laws of phenomena ; in the other, of the causes or exjolanation of these laws. The former must precede the latter, and form its foundation ; the latter must follow the former, and constitute its completion. The change from the one to the other is always attended with prodigious impulse to science. To illustrate : Until Kepler, astronomy was little more than an accumulation of disconnected facts concerning celestial motions — abundant materials, but no science ; piles of brick and stone, but no building. Kepler re- duced this chaos to beautiful order and musical harmony by the discovery of the three great laws which bear his name, and therefore he has been justly called the legis- 1 lator of the heavens — the laivgiver of space. But, had he been asked the cause of these beautiful laws, he could only have answered, '^ The first cause — the direct will of the Deity." A. good answer and a true, but not sci- entific ; because it places the question beyond the do- main of science, which deals only with second or physical causes. But Newton comes forward and gives a physical cause. He shows that all these beautiful laws are the necessary result of gravitation ; and thus astronomy be- 48 WHAT IS EyOLUTIO:^'? comes a physical science. So, until Agassiz, the facts of geological succession of organic forms were in a state of lawless confusion. Agassiz by establishing the three great laws of succession, which ought to bear his name, re- duced this chaos to order and beauty ; and, therefore, he might justly be called the legislator of geological history — the lawgiver of time. But, when asked the cause of these laws, he could only answer, and did indeed an- swer, '^The plans of the Creator." A noble answer and true, but not scientific. Darwin now comes forward and gives, partly at least, the cause of these laws. He shows that all these beautiful laws are explained by the doc- trine of *^ origin of species by derivation with modifica- tions " ; that these laws are not ultimate, but derivative from more fundamental laws of life ; and thus biology is advanced one step, at least, toward the causal stage. Newton and Darwin substituted second causes for first cause — natural for supernatural. They each in his own department broke the bonds of supernaturalism in the domain of Nature. One more important reflection : There are two, and only two, fundamental conditions of material existence — space and time. There are, therefore, two, and only two, cosmoses — space-cosmos and time-cosmos. These have been redeemed from confusion and reduced, to law and order and beauty — changed from chaos to cosmos — ^by science. For this result we are chiefly indebted, in the one case, to Kepler and Newton ; in the other, to Agassiz and Darwin. The universal law, in the one cosmos, is RELATION OF AGASSIZ TO EVOLUTIOX. 49 the law of gravitation ; in the other, the law of evolution. Traced by analysis to its deepest roots of philosophic truth, the one law may be called the divine mode of sus- tentation ; the other, the divine process of creation. Or again : we have all heard of the '^ music of the spheres " — a beautiful and significant name used by the old thinkers for the divine order of the universe — a music heard not by human ear, but only by the atten- tive human spirit. Harmonic relation apprehended by reason we call Law, and its embodiment Science ; the same apprehended by the imagination and aesthetic sense, we call Beauty, and its embodiment Art, music. Now, in music there are two kinds of harmony, simul- taneous and consecutive — chordal harmony and melody. These must be combined to produce the grandest effect. So in cosmic order, too, there are two kinds of harmonic relation — the co-existent in space and the consecutive i7i time. The law of gravitation expresses the universal harmonic inter-relation of objects co-existent in space, the law of evolution, the universal harmonic relation of for 7ns successive in time. Of the divine spheral music, the one is the chordal harmony, the other the consecutive harmony or melody. Combined they form the divine chorus which *^ the morning stars sang together." PART II. EVIDENCES OF THE TRUTH OF EVOLUTION. CHAPTER I. GEXEEAL EVIDEI^CES OF EV0LUTI0:N^ AS A UNIVERSAL LAW. Let us again remind the reader that evolution means, first of all, continuity. The law of evolution, although it doubtless means much more, means, first of all, a law of continuity, or causal relation tlirougliout Nature. It means that, alike in every department of Nature, each state or condition grew naturally out of the immediately preceding. In a word, it means that, in the course of Nature, nothing appears suddenly and without natural cause, but, on the contrary, everything is the natural and usually the gradual outcome of a previous condition. This is noifj admitted by every one in regard to nearly everything : evolutionists apply it to the whole course of Nature. I said this is noio admitted by every one in regard to nearly everything ; but this has not always been so. The world has come to its present position on this subject only by a very gradual process. Let us then trace rapidly the history of the gradual change, for it will prepare us for much that follows. There was a time (and thai^not many decades ago) 54 EVIDENCES OF THE TRUTH OF EVOLUTION. when all things, the origin of which transcends our ordi- nary experience, were supposed to have originated sud- denly and without natural process — to have been made at once, out of hand. There was a time when, for ex- ample, mountains were supposed to have been made at once, with all their diversified forms, of beetling cliffs and thundering waterfalls, or gentle slopes and smiling val- leys, just as we now find them. But noiu we know that they have become so only by a very gradual process, and are still changing under our very eyes. In a word, they have been formed by a process of evolution. "We know now the date of mountain-births ; we trace their growth, maturity, decay, and death ; and find even, as it were, the fossil bones of extinct mountains in the crumjDled strata of their former places. There was a time when continents and seas, gulfs, bays, and rivers, were suj)posed to have originated at once, substantially as we now see them. Now, we know that they have been changing throughout all geological time, and are still changing. Not, however, change back and forth in any direction indifferently and without goal, but gradual change from less perfect to more perfect condition, with more and more comj^lex in- ter-relations — i. e., by 2b process of evolution. We are able now, though still imperfectly, to trace some of the stages of this evolution. There was a time when rocks and soils were supposed to have been always rocks and soils ; when soils were regarded as an original clothing made on purpose to hide the rocky nakedness of the new-born earth. God clothed the earth so, and there an end. Now GENERAL EVIDENCES OF EVOLUTION. 55 we know that rocks rot down to soils ; soils are carried down and deposited as sediments ; and sediments re- consolidate as rocks — the same materials being worked over and over again, passing through all these stages many times in the history of the earth. In a word, there was a time when it was thought that the earth with substantially its present form, configuration, and climate, was made at once out of hand, as a fit habitation for man and animals. Now we know that it has been changing, preparing, becoming what it is by a slow pro- cess, through a lapse of time so vast that the mind sinks exhausted in the attempt to grasp it. It has become what it now is by a process of evolution. The same change of view has taken place concerning the origin of all the heavenly bodies. We may, therefore, confidently generalize — we may assert without fear of contradiction that all inorganic forms, without exception, have origi- nated by a process of evolution. The proof of all this we owe to geology — a science born of the present century. This science establishes the law of universal continuity of events, through infi- nite time, as astronomy does that of universal inter-rela- tion of objects through infinite space. How great the change these two sciences have made in the realm of human thought ! Until the birth of modern astronomy the intellectual space-Jiorizon of the human mind was bounded substantially by the dimensions of our earth ; sun, moon, and stars, being but inconsiderable bodies circulating at a little distance about the earth, and for 56 EVIDEN"CES OF THE TRUTH OF EVOLUTION". our behoof. Astronomy was then but the geometry of the curious lines traced by these wandering fires on the concave blackboard of heaven. With the fiist glance through a telescope the phases of Venus and the satellites of Jupiter, revealed clearly to the mind the existence of other worlds besides and like our own. In that moment the idea of infinite space, full of worlds like our own, was for the first time completely realized, and became thence- forward the heritage of man. In that moment the intel- lectual horizon of man was infinitely extended. So also until the birth of geology, about the beginning of the present century, the intellectual time-horizo7i of the human mind was bounded by six thousand years. The discovery about that time of vertebrate remains, all wholly different from those now inhabiting the earth, revealed the existence of other time-faunas, besides our own and the idea of infinite time, of which the life of humanity is but an epoch, w^as born in the mind of man ; and again the intellectual horizon of man was infinitely extended. These two are the grandest ideas, and their introduction the grandest epochs, in the intel- lectual history of man. We have long ago accepted and readjusted our mental furniture to the requirements of the one, but the necessary readjustment to the other is not 3"et complete. All inorganic forms, then, it is admitted, have come by evolution. But how is it with organic or living forms ? Let us see. Every one knows, because it is within the limits GENERAL EVIDENCES OF EVOLUTION. 57 of ordinary experience, that every individual organism now originates and gradually becomes what we see it, by a natural process — that is, by evolution. If, then, there be any exception, it must be only i\\e first of each kind. But what kind ? There are many kinds of kinds ; classes, orders, families, genera, species, varieties. Now, many of these kinds can be shown to have become what we see them by a gradual process similar, at least, to evolution. Take for example, classes. The class of fishes and the class of reptiles are now widely distinct and have little in common except a vertebrate structure ; but, as already shown, page 12, this extreme difference has not always existed. On the contrary, the earliest representatives of these two classes so merged into one another that each seemed either. From this common stock the two classes were gradually separated, each going its own way and be- coming more and more widely distinct even to the pres- ent day. There can be no doubt, therefore, that these tivo classes, as we now know them, have lecome what they are by a gi'adual process. Again : In the whole realm of Nature there is not a class more distinctly separate from every other and without intermediate links than birds. But this has not always been so. They have gradually become so. The earliest birds were so reptilian in struct- ure and appearance that if we could see them now we would be in doubt whether we should call them birds or reptiles. Birds have gradually separated themselves from the reptilian stem, becoming more and more bird-like from age to age, until now, at last, the two classes are 58 EVIDENCES OF THE TRUTH. OF EVOLUTION. wholly separated and the intermediate links destroyed. So far as external eharacters are concerned, birds may be said to have finally and wholly released themselves from entangling alliance with any other class. Classes, then, it will be admitted, have undoubtedly become what we now know them by a very gradual pro- cess following laws identical (as we have already seen, page 19) with the laws of evolution. Shall we try or- ders ? Of the class Mammalia there are two well-rec- ognized and widely-distinct orders, viz., the Carnivores and the Herbivores. We all know how widely diverse these are in form, in structure, in habits, and in food. Has it always been so ? Have these been made so at once ? By no means. They have gradually become so. The earliest mammals were neither the one nor the other distinctively. They were omnivores, completely interme- diate in food, habits, form, and structure. From this common stock the two orders have gradually separated, the carnivores becoming more and more adapted to one mode of life and the herbivores to another, by a process following the laws of evolution, as already explained. Shall we try families and genera ? Marsh and Huxley have shown us how completely the horse family {EquidcB) and the horse-genus (Equus) illustrate the process of gradual becoming and the law of evolution. Under their guidance, we see that the earliest traceable ancestor of the horse family, before it was distinctively a horse fam- ily at all, had on the fore-foot five toes in the Lower Eocene, four toes in the Upper Eocene, and three toes in GENERAL EVIDENCES OF EVOLUTION. 59 the Miocene ; then we see the two side-toes shortening up more and more in the Pliocene and becoming rudiment- ary splints, leaying only one toe in the Quaternary and present epochs. Thus, the side-splints in the foot of the modern horse tell the story of its three-toed ancestry. Similar gradual changes are clearly traceable in size, shape, structure of limbs, of teeth, and of brain. In all respects the members of the horse family have become more and more horse-like in the course of time. This subject will be taken up and more fully illus- trated, under the head of special evidences, in a subse- quent chapter. We here touch it only sufiSciently to illustrate this universal law of gradual becoming. We have taken only a few examples, but the same is undoubtedly true of all Taxonomic groups above species. Passing over these last for the moment, we take next races and varieties. These smaller groups are admitted by all to be formed by a natural process, because not only can we make them artificially, but all the intermediate links may be found in Nature. So we have only species re- maining. Yes; species are imagined by the old-school naturalist and by the anti-evolutionist of to-day as the ultimate elements of Taxonomy. This, then, is the last ditch upon which the defense of sui^ernaturalisni in the realm of Nature is made. "Other groups," they say, "may have gradually become what they now are by the successive introduction of specific forms according to a preordained plan which is well expressed by the formal laws of evolution. But species are without transition 60 EVIDENCES OF THE TRUTH OF EVOLUTION". forms. They come in suddenly, remain unchanged while they continue, and finally pass out suddenly, so far as specific characters are concerned. Kew species come in their places by direct act 'of creation — by suhstitutioiij not by transmutation." This, then, is the last intrench- ment. Can we give any good evidence of gradual forma- tion of species ? I believe we can. First, then, it is admitted that we can easily make varieties and races artificially. "We will not 7ioiv describe the process; we are all familiar with the results, viz., the varieties of domestic animals and of useful and orna- mental plants ; the extremely different breeds of horses, cattle, sheep, dogs, pigeons, etc. ; of wheat, cabbages, turnips ; of roses, dahlias, etc., etc. No one will doubt that the extreme varieties of any of these, say greyhound and pug, if wild, would be called distinct species, or even distinct genera. We do not call them so, for two reasons : first, because we see them made ; and, second, because we find all intermediate links between them ; and the usual definition of species is that they can not be made, and they have no intermediate links. Thus, then, the question is narrowed down to wild species. They say : **We take our stand on these" (surely a very narrow ground for so broad a philosophy). ''We defy you to show gradual formation with intermediate links." Now, in fact, by diligent search such intermediate links between well-recognized species have been found in some cases, especially in birds, on account of their great power of dispersal. Certain forms have long been known GENERAL EVIDENCES OF EVOLUTION. 61 from widely-separated regions, and universally regarded as distinct species, as distinct as any. Then, by minute examinations of intermediate regions, a complete series of intermediate forms has been picked up. This has oc- curred not only in one case but in many cases, and not in birds only but in many other classes — examples in- crease with our increasing knowledge.* The only answer to such eyidence is that these are not true species, Now, see the fallacy lurking here ! They define species as ul- timate elements of taxonomy, as distinct and without intermediate links, and then require us to find such in- termediate links ; and, finally, when with infinite pains some such links are found, they say : " Oh ! I see ; we were mistaken ; they are only varieties ! ! " It is true that naturalists, when intermediate links are found, usu- ally put all together as one species, but this they do purely for the sake of clearness of definition and descrip- tion. It is freely admitted by the evolutionist that spe- cies are 7ioio usually distinct and without intermediate links, these having been destroyed in the struggle for life. This will be fully explained in another chapter. It is also freely admitted that although intermediate links must have existed at one time, their remains are rarely found. The reason of this will also be explained hereafter. Nevertheless, in some cases, as already seen, we do find them still existing. Now, we add that in some cases, where they no longer exist; we find them in * Cope, "Science," vol. ii, p. 274, 1883. 62 EVIDENCES OF THE TRUTH OF EVOLUTION. the form of fossil remains. The most remarkable exam- ple of this is found in the gradual changes in the forms of Planorbis in the fresh-water deposits of Steinheim^ as shown by the admirable researches of Hyatt.* We shall discuss these also more fully in another place. ISTow, if there be any such links at all, however rare, then every objection to the derivative origin of species is removed. Perhaps it may be well to make bare mention of another kind of evidence, viz., the actual change of spe- cies under the eyes, by the action of change of environ- ment. The different species of the genus Artemia (a low form of crustacean) live in brine-pools. By concentrat- ing the brine of such a pool, one species {A. salino) has been observed to change in successive generations into another {A, Muhlhausenii), and the latter back again to the former by slow freshening, f Again : The siredon and the amblystoma have always, until recently, been re- garded as not only distinct species, but distinct genera of amphibians. Siredon was supposed to be a permanent gill-breather, while amblystoma becomes by metamorjoho- sis a pure air-breather. Now, however, it is known that the former mav chansre into the latter. But the most curious part of the life-history of these animals, is that if water be abundant the siredon reproduces freely, and remains indefinitely a gill-breather ; but if the water dries up it changes into the lung-breathing amblystoma. * Boston Society of Natural History — anniversary memoir, 1880. Also, " American Naturalist," June, 1882. f "Archives des Sciences," vol. liv, 1875. GENERAL EVIDENCES OF EVOLUTION. 63 We do not give this as examples of change of species, for the change is in the individual life, and therefore in the nature of metamorphosis, but as evidence of the power of physical conditions in modifying the develop- ment of organic forms and therefore of the manner in which gill-breathers were j^robably transformed into air- breathers. To sum ujo : 1. All inorganic forms, without excep- tion, have become what we find them by a natural pro- cess — i. e., by evolution. 2. All organic or living forms within the limits of observation, i. e., every living thing, has become what we now see, by a gradual, natural pro- cess — i. e., by evolution. 3. All taxonomic groups, except species, have undoubtedly become what we now see them by a gradual process, following the laws of evolution, and therefore presumably by a natural process of evolution. 4. By artificial means, breeds, races, etc., very similar, at least in many respects, to species, are seen to arise by a gradual natural process — i. e., by evolution. 5. In some instances, at least, natural species are observed to j^ass into one another by intermediate links in such wise that we are forced to conclude that they have been formed by a natural process. May we not, then, safely generalize, and make the law universal ? Is not this a sufficient ground for confi- dent induction ? Even though some facts are still inex- plicable, is that a sufficient reason for withholding assent to a theory which explains so much ? In all induction we first establish a law provisionally from the observation 64 EYIDENCES OF THE TRUTH OF EYOLUTIO^^. of a comparatively few facts, and then extend it over a multitude of facts not included in the original induction. If it explains these also, the law is verified. The law of gravitation was first based on the observation of a few facts, and then verified by its explanation of nearly all the facts of celestial motion. There are some outstand- ing facts of celestial motion still unexplained, but we do not, therefore, doubt the law of gravitation. The same principle applied in biology ought to establish the law of evolution, for it also explains all the facts of biology as no other law can. But inductive evidence differs from other kinds of evidence in one respect, which, in fact, constitutes its strength to the scientific, but its weakness to the popular mind. It is a kind of circumstantial evi- dence, but its force does not consist in a few strong cir- cumstances easily appreciated, such as strike the popular mind, and force conviction, but rather in a multitude of small circumstances, each by itself insignificant, but all together pointing to one conclusion and demanding one explanation. Such evidence is, indeed, overwhelming, but only to the mind that masters it. The evidence for the law of gravitation is literally the whole science of as- tronomy. So also the evidence for the law of evolution is the whole science of biology. Neither of these laws can be proved in a debating society, but only by a course of study. In the one case the law has been universally ac- cepted — not, however, on evidence, for there are few in- deed who appreciate the evidence, but on the authority of scientific unanimity. In the other case there has not GENERAL EVIDENCES OF EVOLUTION. 05 yet been time enough for the already established unanim- ity to have its full effect. Thus much, we belieye, will be generally admitted as a yery moderate claim. Evolution is certainly a legiti- mate induction from the facts of biology. But we are prepared to go much further. We are confident that evolution is absolutely certain. Not, indeed, evolution as a special theory — Lamarckian, Darwinian, Spencerian — for these are all more or less successful modes of explain- ing evolution ; nor evolution as a school of thought, with its following of disciples — for in this sense it is still in the field of discussion — but evolution as a law of deri- vation of forms from previous forms ; evolution as a law of continuity, as a universal law of becoming. In this sense it is not only certain, it is axiomatic. It is only necessary to conceive it clearly, to see that it is a neces- sary truth. This may seem paradoxical to some. I stop to justify it. Physical phenomena we all admit follow one another in unbroken succession, each derived from a preceding, and giving origin to a succeeding. We call this the law of causation, and say that it is axiomatic. We might call it a law of derivation. So also natural /orms, organic or other, follow one another in continuous chain, each de- rived from a preceding and giving origin to a succeeding. We call this a law of derivation. We might call it a laiu of causation, and say that it too is axiomatic. The ori- gins of new phenomena are often obscure, even inexplica- ble, but we never think to doubt that 'they have a natural QQ EVIDENCES OF THE TRUTH OF EVOLUTION. cause ; for so to doubt is to doubt the yalidity of reason, and the rational constitution of Nature. So also the ori- gins of new organic forms may be obscure or even inex- plicable, but we ought not on that account to doubt that they had a natural cause, and came by a natural process ; for so to doubt is also to doubt the validity of reason, and the rational constitution of organic Nature. The law of evolution is naught else than the scientific or, indeed, the rational mode of thinking about the origin of thi^igs in every department of Nature. In a word, it is naught else than the law of necessary causation applied to forms instead of phenomena. Evolution, therefore, is no longer a school of thought. The words evolutionism and evolutionist ought not any longer to be used, any more than gravitationism and gravitationist ; for the law of evolution is as certain as the law of gravitation. Nay, it is far more certain. The nexus between successive events in time (causation) is far more certain than the nexus between coexistent objects in space (gravitation). The former is a 7iecessary truth, the latter is usually classed as a contingent truth. I have used and may continue to use the term evolutionist, but if so it is only in deference to the views of many intelligent per- sons, who do not yet see the certainty of the law. CHAPTER 11. SPECIAL PROOFS OF EVOLUTION". Introductory. It will be seen from the preceding chapter that we regard the law of eyolution in its wider sense, viz., the derivative origin of all forms, organic or other, as axio- matic, and therefore requiring no further proof. Among scientific men there is no longer any discussion of the truth of this law, but only of the theories of the causes of the law. We believe that to the scientific mind there is no other rational mode of looking at the subject of origin of organic forms. To such a mind, therefore, all that follows is but the deductive application of that law in the explanation of the phenomena of organic Nature. But it takes time for the popular mind to readjust it- self to new and revolutionary truth. Many minds, even among the most intelligent, have not yet accepted this as the only rational mode of thought. Many men require iwYthev special proof s oi the derivative origin of organic forms. Even to those who accept evolution, these proofs will be interesting as illustrations of such origin. We 68 EVIDEXCES OF THE TRUTH OF EVOLUTION. will attempt to bring out these proofs under several Leads, the most important of which are : 1. Proofs from morphology, or the general laws of animal structure ; 2. Proofs from embryology ; 3. Proofs from geographical distribution of organic forms ; and, 4. Proofs from artifi- cial breeding. The subject is so yast that all we can do is to touch lightly only the most salient points under each of these heads ; for, as we have already said, the evi- dence is really nothing less than the whole science of biology. Prej^aratory to this, however, it is necessary to bring out a little more fully than before (page 29), though still only in outline, the two antagonistic views, which may be called the old and the new, or the natural and the supernatural, of the origin of new organic forms, especially species. Origin of New Organic Forms ; the Old View briefly stated. — According to the old-school naturalists, species are the ultimate elements of taxonomy : genera, families, orders, etc., may gradually change their character from age to age, by the introduction of new species ; but spe- cies were supposed to be substantially permanent. It was necessary to have some unit for convenience of descrip- tion and classification, and this was found to be the best because most stable. As in nearly all cases of beliefs, this doctrine was held at first somewhat loosely, as a pro- visional and convenient view — as a good working hy- pothesis — but gradually, under pressure of controversy, became more strictly formulated, and, as it were, hard- ened into a scientific dogma, especially in- the hands of SPECIAL PEOOFS OF EVOLUTION. 69 Agassiz. According to this view, the first pair or pairs of each specific kind originated we know not how, but certainly at once in its present form in full perfection, and, therefore, presumably by direct creative act of Deity ; and then afterward by the law of generation con- tinued to produce others of the same pattern indefinitely. Moreover, the first one or more pairs of each kind multi- plied and spread abroad in every direction, each from its own center of origin, as far as physical conditions and struggle for life with other species would allow. This idea explains tolerably well the geographical distribution of species as we now find it. For example, species on different continents are widely different, because those on each have originated independently where we now find them, and spread in all directions as far as physical conditions would allow, but could not reach other con- tinents because of the ocean-barrier. That this is the only reason they are not there, is shown by the fact that, if they are carried there, they usually do perfectly well. Even on the same continent, for the same reason, species may be very different if separated by impassable barri- ers such as high mountain-chains or by climate. But wherever one group of species, originating in one place, comes in contact on the margin of tlieir range with another group of species originating in another place, we see no evidence of transmutation of one form into another, but only suistitution of one fully-formed spe- cies for another equally fully formed. Therefore, we must conclude that physical conditions may limit the 70 EVIDENCES OF THE TRUTH OF EVOLUTION. range of a species, but can not transmute it into another. Thus, to say the least, many of the facts of geographical distribution are well explained by this idea of creative origin in specific centers and subsequent permanence of specific form. We say many of the facts ; we will show hereafter that not all can be thus exj^lained. But the main question is not of geographical but of geological distribution ; not distribution in space, but succession in time. Species do not continue forever. On the contrary, they have changed many times in the course of geological history. As conditions become un- favorable, species die out or become extinct, and others take their place and carry forward the life and develop- ment of the organic kingdom. Now, how do they change ? According to this school of thought, here also, as in geographical distribution, they are not transmuted but replaced ; here also physical conditions may destroy a species, but can not transform it into another. As spe- cies die out, others are created at once, out of hand and fully formed in their place ; but in accordance with a preordained plan consistently carried out and working ever toward higher and higher conditions. Thus, life is continued on the earth by the alternation of supernatu- ral and natural processes ; by the alternate use of direct and indirect action of Deitv : direct in the introduction of first pairs, indirect through the natural process of re- production in the continuance and multiplication of the species. Each sjiecies is made according to a pattern in the -Divine mind, on a sort of intellectual die, and then SPECIAL PROOFS OF EVOLUTION". 71 continues to reproduce a succession of individuals of the same pattern as if struck from the same die until the die is broken or worn out. Another die is made, of another pattern, and individuals are struck from this ; and so on, throughout the whole geological history of the organic kingdom. Only, we must add that the successive dies are made to follow one another according to a plan which is expressed by the three laws already given on page 11. Thus, the origin of individuals is natural, the origin of species supernatural ; the making of dies is supernatu- ral, the coinage is natural. We have stated this view in a too extreme form, in order to make it clearer. We now, therefore, proceed to qualify somewhat. Specific types were held, by writers of this school of thought, to be siibstantially but not absolutely unchangeable. Successive individuals of the same species were admitted to be not exactly alike. Such slight differences were called varieties. It was ad- mitted, indeed, that species varied, but it was believed that such variations in any direction were strictly limited in amount. A species may be compared to a right cyl- inder standing on end. As such a cylinder may be tilted slightly in one direction or another, without overthrow- ing its equilibrium, the cylinder tending ever to right itself and return to its original position, so a species may be varied slightly in one direction or another with- out destroying its integrity, the species tending ever to return to its normal or typical form. But as the cylin- der, if pushed too far from its normal position, is over- 72 EVIDENCES OF THE TRUTH OF EYOLITTrON. thrown, so also a species, if pressed too far in the way of variation from its typical form, is destroyed, but not changed into another species. As cylinders may be more or less rigid, depending upon the breadth of their bases, so also some species are more rigidly set in their typical form, and some are more plastic to influences causing Tariations, but in all cases there is a limit to the amount of oscillation consistent with integrity. The New View briefly stated. — According to Darwin, and all biologists of the present day, species are variable without limit, if only the causes of change are constant and slow enough in their operation, and the time long enough. A sj)ecies must be in harmony with its environment, for this is the condition of its existence. Now, if the envi- ronment change, the species must tend to change slowly from generation to generation, so as to readjust its rela- tions in harmony with the changing environment. If the change of environment be slow, the readjustment may be successful, and the species will change gradually into another form, so different that it will be called a different species, especially if the intermediate gradations be destroyed. If the change in the environment be too rapid, many species, especially the more rigid, will be destroyed, while the more plastic may survive by modifi- cation. Thus, at every step in the evolution of the or- ganic kingdom, some species have died without issue, while others have saved themselves by changing into new forms in harmony with the new environment. Compar- ing to a growing tree, some branches overshadowed die. SPECIAL PKOOFS OF EVOLUTION. 73 while others push on for light, forming new lateral buds, and dividing as they grow. By continued divergent change species gradually become genera, genera families, etc. Thus, varieties, species, genera, families, orders, classes, etc., are only different degrees of differences formed all in the same way. Varieties are only com- mencing species, species commencing genera, and so on. There is no making and wearing out of dies, and making of new ones ; the whole process is a natural one— the whole series is genetically connected. In a perfect classi- fication varieties, species, genera, families, orders, classes, etc., are only different degrees of llood-Mnsliip, So much may be regarded as certain, and out of the field of discussion among biologists of the present day. It is only in defining this process more accurately, and especially in the theory of the causes or factors of evolu- tion, that there are still difference and discussion. The most probable view on this subject we now proceed to give. Factors of Evolution. — The causes of change or adapt- ive modification, or the factors of evolution, are at least four well known, and probably many more still un- known : 1. The physical environment — heat and cold, dryness and moisture — affects function of organs, and function affects structure, and both changed function and changed structure are inherited by offspring, and so increased from generation to generation, becoming greater without limit. 2. Increased use or disuse of organs enforced or permitted by change in the environ- 74 EVIDENCES OF THE TRUTH OF EYOLUTIOX. ment, physical or organic, or both, induces change iu form, size, and structure of the organs ; and this change is inherited by the offspring, and so from generation to generation small differences are integrated until they be- come great without limit. These two factors were recog- nized bv Lamarck. 3. "^N'atural selection," or ^'^ survival of the fittest," among divergent varieties of offspring. This is the distinctive Darwinian factor. In the two preceding factors the change is during the indivichial lifetime, and reproduction is supposed to transmit it un- changed to the offspring. In this factor, on the con- trary, the form and structure are supposed to remain un- changed during the individual life, but for some unknown cause there are slight variations in different directions (divergent) in the offspring from the same parents. Now, when we remember that by rejiroduction the num- ber of individuals tends to increase by geometrical pro- gression, and that in each generation only a very few (on an average only two from all the offspring of one pair) can survive, it is evident that among these divergent va- rieties those will most likely survive which are most in harmony with the external environment, and which pos- sess the most efficient organs of defense or of escape, or for food-taking. The surviving offspring, therefore, will be on the average better in these respects than their par- ents. It matters not how little better, for the integration of even infinitesimal improvements from generation to generation will eventually produce any required amount of change. 4. To the above Darwin has added also SPECIAL PROOFS OF EVOLUTION. 75 ** sexual selection." In 7iatural selection there is struggle of all for food, or means of livmg. In sexual selection there is a struggle among the 7nales for possession of the female, and the means of procreation. The one is con- nected with the nutritive appetite, the other with the reproductive appetite. This mode of selection acts in two ways, by the law of battle and the law of attractiveness. The strongest or the most attractive males alone, or mainly, leave offspring, which, of course, inherit their peculiarities ; and these are increased indefinitely by integration through successive generations, thus increas- ing the strength or the beauty. Of these two laws, the law of battle is most conspicuous among mammals, and the law of attractiveness among birds. It is evident that this factor can not operate among many lower animals which are hermaphroditic, nor among plants. Of these acknowledged factors of evolution, the first two were known to Lamarck and the older evolutionists. The third and fourth are distinctively Darwinian. Ac- cording to Darwin, while all these are operative, the third is the most powerful ; but Spencer accords this distinc- tion to the Lamarckian factors. Most American zoolo- gists take the same view. Such until very recently were all the recognized fac- tors of evolution. But, within the past year (1886) has taken place, it seems to us, the most important advance in the theory of evolution since Darwin. It is the sugges- tion by Mr. Catchpool, * and afterward the more full elab- * "Nature," vol. xxxi, p. 4, 1884. TG EVIDENCES OF THE TRUTH OF EVOLUTION. oration by Dr. Eomanes, of anotlier factor, which he calls ^'physiological selection. " * The great objections to the sufficiency of the theory of evolution, as left by Darwin, were twofold. : 1. While natural selection accounts completely for the formation of useful structures or adaptive modifications, and therefore for differences characterizing classes, orders, families, and even genera — for these are all adaptive — it can not so comj^^letely account for those constitut- ing species ; for these consist mostly of trivial differ- ences in coloration, relative proportion of parts, which are of no perceivahU use in the struggle for life, and therefore could not be preserved and integrated by natural selection. Therefore, according to Komanes, natural selection is a theory of origin of adaptive struct- ures rather than of origin of species. Comparing to a growing tree, once admit lateral buds started, and nat- ural selection completely accounts for the growth in dif- ferent directions, and therefore for the profuse ramifica- tion ; but the origin of the lateral buds is not explained. 2. The second difficulty is as follows : Such com- mencing differences as constitute varieties and species not only would not be i)reserved and integrated by nat- ural selection unless useful, but would immediately be sivamped hy cross-hreeding with the parental form. But, as the whole divergence commences in varieties, evi- * See abstract of Dr. Romanes's views, "Nature," vol. xxxiv, pp. 314, 336, 362. Also, discussions of the same by Meldola, Galton, Wallace, etc., in immediately subsequent numbers. SPECIAL PROOFS OF EVOLUTION. 77 dentlj it could not commence at all unless this cross- breeding be in some way prevented. This may, indeed, be done, without the assumption of any new factor of eYoliition, hy 7)1 igr at ion J and, hence, migration must be regarded as an important agent in the creation of new forms, not only by the effect of a new environment, but also by prevention of the swamping of commencing species by cross-breeding with the parental form ; but in a crowded locality, without outlet for migration (the very conditions most favorable for severe competitive strug- gle, and therefore for most potent operation of natural selection ; and therefore, also, according to Darwin, for profuse diversification), commencing varieties could not pass into species, because swamped by cross-breeding. Once the divergence reaches the point of cross-sterility — i. e., of species — then, indeed, by true breeding, charac- ters, even tliough not useful, may be preserved. But how is it to commence ? This difficulty has been severely felt by all Darwin- ists. It seems to us that it is largely met by Dr. Eo- manes. According to Romanes, no organ is so subject to varietal changes as the reproductive, and these in no respect so much as in degrees of fertility. Unfortunate- ly, these changes are not visible, and must be judged of only by the results. It is not uncommon, for example, to find, sterility between individuals (sexual incompatibility) who are both of them perfectly fertile with other indi- viduals. Similarly, cross-sterility, partial or complete, is not uncommon between varieties or races, as Mr. Darwin 78 EVIDENCES OF THE TRUTH OF EYOLUTIOK lias long ago noticed. It very generally, as we know, occurs between, and, in fact, is constantly used as a test of, si^ecies. Now, this cross-sterility with parent stock, which we find so constant a character of species, and which, therefore, must have commenced as a partial cross- sterility in varieties, is it antecedent or consequent to other variations 9 It has been usual to suppose it conse- quent to a certain amount of divergence, viz., that which constitutes, or at least approaches, species. But, accord- ing to Eomanes, it is antecedent. Among many other variations, this is that one which originates species, be- cause it prevents reversion by cross-breeding with the parent stock, and insures true breeding with its own kind. In a word, it sexually isolates the species. Sup- pose, then, a species multiplying indefinitely in one lo- cality : trivial variations of many kinds, and in many directions, occur among the offspring. These are merged by cross-breeding into the original type, which, there- fore, remains unchanged. But, from time to time, among these variations there occur some affecting the reproduc- tive organs in such wise as to produce partial or complete cross-sterility with the parent form. This is the begin- ning of a new species. It breeds true with its own kind, and therefore all the associated variations external and visible, and therefore constituting species, although triv- ial and of no use in the struggle for life, are preserved. This view completely accounts for the cross-fertility of artificial breeds equivalent in other respects to species ; for cross-sterility is not an end aimed at by the breeder, SPECIAL PROOFS OF EVOLUTION". 79 it being easy to prevent cross-breeding, if desired, by artificial isolation. But, if this yiew be true, species from widely-diiierent geographical regions ought also to be often cross-fertile, because, having been formed by geographical isolation, sexual isolation was not a neces- sary factor in their formation. This point deserves test- ing by careful observation. It may be, and has been, objected to Dr. Eomanes's claims, that this is no new factor ; that physiological selection is only a form of natural selection. This objec- tion, it seems to us, is little more than a play upon words. It certainly is selection, and by a natural pro- cess, and therefore in some sense a natural selection, but not in the sense of Darwin. It is not a selection of indi- viduals fittest to survive ; for cross-fertile individuals are as fit to survive as individuals, though not as species, as are cross-sterile. Natural selection is intent only on pre- serving the best individuals ; physiological selection on preserving the kind. Natural selection continues the direction of progress unchanged ; physiological makes new directions. It will be observed that Darwin and his followers take divergent variations of offspring simply as a known fact, upon which natural selection operates to produce progressive modification. And, as the cause of variation in offspring is wholly unknown, such variations are often spoken of as fortuitous. But, of course, it is well under- stood that nothing in Nature is really fortuitous. They may, however, for all jourposes of natural selection be 5 80 EVIDENCES OF THE TRUTH OF EVOLUTION. thus regarded until we know their cause. It is evident, then, that if we, with Darwin, take natural selection as the most important known factor, the really most impor- tant cause of evolution is the cause of varieties. This is the unhnown fundamental factor. As Darwin reduced Agassiz's three formal laws of succession to more general laws of life, and thus made one important step in the advance of biological science, so he who shall explain the cause of divergent variation will make another important step by reducing the phenomena to still more general and fundamental laws of life. In conclusion, let me again impress upon the reader that all the doubt and discussion, above described, as to the factors of evolution, is entirely aside from the truth of evolution itself, concerning which there is no differ- ence of opinion among thinkers. Haying now prepared the mind of the reader, by stat- ing briefly what it is we wish to prove, we x)roceed to give some of the most im^Dortant of these proofs. • CHAPTER III. SPECIAL PROOFS, TAKEN FROil THE GEXEKAL LAWS OF AKIMAL STRUCTURE, OR FROM COMPARISON" 11^ THE TAXONOMIC SERIES. General Pri7ici2jles. Analogy and Homology. — In biology those organs or parts in different animals are said to be analogous which, however different their origin, have a general similarity of form and especially of function.; while those are called homologous which, however different their general ap- pearance, and however different their function, yet may, by close examination and extensive comparison, be shown to be modifications of one another — to be, in fact, origi- nally the same part modified for different purposes. In the former the parts compared look and behave as if they were the same, but are not ; in the latter they look and behave entirely differently, but are, in fact, the same part in disguise. We can best make this plain by examples. The wing of a bird and the wing of a butterfly are analogous or- gans. They have the same function — i. e., flying; and this function necessitates the same general form of a flat 82 EVIDENCES OF THE TEUTH OF EVOLUTION. plane. But they are not at all homologous ; they are not at all the same organ or part. They certainly have never been formed one out of the other by modification. But the wing of a bird, the fore-paw of a reptile or mammal, the wing of a bat, and the arm and hand of a man, though so different in form and function, are homologous parts. On close examination they are found to have the same general structure, to be composed of essentially the same pieces, although they are so greatly modified in or- der to adapt them to different functions, that the general or superficial resemblance is now lost. Their structure is precisely such as it would be if they had all originated from some archetypal fore-limb by modifications in dif- ferent directions of its several parts. By extensive com- parison in the taxonomic and ontogenic series, all the intermediate gradations between these extreme modifica- tions may be i:)iclved up. Another example. The lungs of a mammal and the gills of a fish are analogous organs, since they have the same function of aeration of the blood. But they are not at all homologous : they are not built on the same plan ; by no effort of the mind can we imagine that the former could have come out of the latter by modifica- tion. On the contrary, we have positive proof that it did not so come. But there is an organ in the fish which is homologous with the mammalian lung, viz., the air- bladder, or swim-bladder. We know it — 1. Because we can trace in the taxonomic series all the gradations from the one to the other. In most fishes the air-bladder is SPECIAL PEOOFS. 83 wholly cut off from the gullet, and only very feebly sup- plied with blood. It is used and can be used only for flotation. In others, as the gar-pike, the swim-bladder is quite yascular and opens by a tube into the throat. Through this optening air is gulped down from time to time into the bladder, and again from time to time ex- pelled. In other words, this fish supplements its gill- breathing by an imperfect lung-breathing. We have here the beginning of a lung. In still other fishes, viz., the Dipnoi {lepidosireii and ceratodus, Fig. 2), the air-blad- FiG. 2. — Lepidosiren. der becomes a more perfect lung — i. e., a very vascular sacculated sac ; and there is not only an opening into the throat, but also from the throat to the snout. In other words, we have for the first time nostrils. These fishes completely combine gill-breathing w^ith lung- breathing. The step from these to the lowest am- i^hibian reptiles is so small, that some have classed the lepidosiren among amphibians instead of fishes. The siredon or axolotl of Kew Mexico, the nee turns or meno- branchus of our Northern lakes, and the siren of our Southern swamps, have both gills and lungs, and breathe both air and water ; but the lung is very imperfect, beings only a sacculated sac, like the air-bladder of the cerato- 84 EVIDENCES OF THE TRUTH OF EYOLUTIOK dus and le23idosiren. ^No one doubts that the air-breath- ing organ of an amphibian is a true lung ; yet we have traced all the gradations between it and the air-bladder of a fish. We conclude, therefore, that if there be any such thing as transmutation of organic forms, the lung of higher animals must have been formed by the process aboYe described.* But we know it still more certainly— 2. Because we can trace the change from the one to the other in the on- togenic series. In the life-history of the individual we can actually see the one thing change into the other. The frog, as is well known, w^ien first hatched, is a tadpole. It has no legs, but locomotes by means of a yertically- expanded taih It has no lungs, but breathes water in- stead of air, by means of gills. It is in all respects, therefore, a fish, and would be classed as such if it re- mained in this condition. But it does not ; it gradually loses its tail and gills, and acquires legs and lungs, and breathes air only. JSTow in this change whence came the lungs ? From the gills by modification ? K'o ; but from an organ similar in character and position to the air-bladder of a ceratodus, or a lepidosiren. This organ has gradually developed into a Inng. The steps of the change are briefly as follow : First, the breathing is wholly water-breathing by gills. Next, by the develop- ment of this other organ, it is partly water-breathing by * While all comparative anatomists agree that the lung is a diver- ticulum from the oesophagus, like the air-bladder of the gar-fish, some think that it is a different diverticulum, which is seen first in the dipnoi. SPECIAL PROOFS. 85 gills, and partly air-breathing by lungs. Lastly, the gills gradually dry up, and the lungs develop more and more, until the breathing is wholly by lungs. We have dwelt somewhat upon this example, because it is an excellent example of what we mean by homology, and also because we will have occasion to use it again. But so important, for all that follows in this part, is a clear idea on the subject of homology, that it will be best to familiarize the mind of the reader with it by means of a few examples drawn from plants. A potato is analogous to a root — a tuberous root like that of a dahlia or a sweet-potato — but is not at all ho- mologous with these. On the contrary, it is homologous with a stem. It is essentially an underground, leafless branch, which has thickened enormously at the point by accumulation of starch. The evidence of this is found in the fact that it has rudimentary leaves (scales) ar- ranged in regular spiral order of phylotaxis, each with its axillary bud (eyes). It is still more clearly shown by the fact that buds above-ground which, if let alone, would form leafy branches, may be made to become tu- bers by covering them with earth or dead leaves, and thus excluding the light ; and, conversely, underground buds which, if let alone, would form tubers, may be made to grow into leafy branches by exposing them to the light. Take another example : The broad, flat, elliptical, green masses so characteristic of the cactus family, and usually called their leaves, are indeed analogous to leaves 86 EyiDE:N"CES OF THE TRUTH OF EYOLUTIOX. in color, form, and function ; for they are green and flat, and assimilate carbonic acid and water (CO^ and H^O) like leayes. But they are not, in truth, leaves, but modified stems, for they have the essential structure of stems, with their pith, wood, medullary raj^s, and bark, and may be traced through all gradations into the ordinary cylindrical form of stems. "Where are their leaves, then? Their spines are their abortive leaves. These are arranged spirally like leaves, and bear buds in their axils like leaves. They are, in truth, leaves, modified to perform the function of defensive armor ; while their function has been delegated to the stem flattened for this pur23ose. One more examj^le : The acacias, of which there are fifteen to twenty species in California, introduced from Australia, form two grouj^s having extremely different styles of leaves. "We will call them the feather-leaved and the simple-leaved acacias. In the former, the leaves are very finely bipinnate, and the general asj)ect of the foliage is extremely feathery and graceful. In the latter the leaves are simple, ovate, and, curiously enough, set on edge ; and the general aspect of the tree is therefore rather stiff. It seems at first incredible that leaves so different and asj)ects so diverse should belong to plants of the same genus. But a little close examination shows that, as usual, the botanists are right and the popular judgment wrong. The plumose-leaf is the normal leaf- form for this genus. The simple leaf is not only abnor- mal, but in a homological sense is not a leaf at all— i. e.. SPECIAL PEOOFS. 87 it does not correspond to the part called the hlade in ordinary simple leaves of other trees. In the seedling of the simple-leaved acacias, and sometimes for a consider- able time in the young tree, the leaves are all plumose. As the tree matures it gradually changes its dress and puts on its toga virilis. The gradual change from the Fig. 3. — A branch of young acacia, showing change from one form of leaf to the other ; a, 6, c, (7, successive stages of change ; l^ s, leaf stalk which gradually changes into the blade in c, , degenerate forms like snakes and some lizards, which have lost their limbs by disuse. So much concerns the general plan of skeletal structures, and is strons^ly suo^orestive of — in fact, is cavity ; r, visceral ^ & .; && ^ ? ^ cavity ; c, centrum of inexplicable without — common ori- gm. But much more remains which is not only suggestive, but demonstrative of such origin. By extensive comparison in the taxonomic and ontogenic series, the whole vertebrate structure in all Fig. 4. — Diagram cross- section tlirou2;h the body of a vertebrate, showing the relation of skeleton to the cavities, n. neutral PROOFS FROM HOMOLOGIES. 95 its details in different animals may be shown to be modi- fications one of another. Sometimes a piece is enlarged, sometimes diminished, or eyen becomes obsolete ; some- times several pieces are consolidated into one ; but, in spite of all these obscurations, corresponding parts may usually be made out. This is the main subject of this chapter. Special Homology of Vertebrate Limbs.— It would lead us much too far into unfamiliar technicalities to take up the whole skeleton. We select the limbs, both because their general structure is more familiar, and be- cause in them the two fundamental ideas of essential identity and of adaptive modification are both admirably illustrated. The reason of this is, that it is by the limbs that the organism chiefly reacts on the environment, and is modified by it. Fore-limbs. — In the accompanying figures (Figs. 5- 18) we have represented, side by side, the fore-limbs of many vertebrates, taken from all the classes — mammals, birds, reptiles, and fishes. For convenience of compari- son, the corresponding parts are similarly lettered in all. Also, in order to identify easily certain important corre- sponding segments, we have drawn through them a con- tinuous dotted line. In man, nearly all the parts are present, and his limbs, therefore, may be taken as a term of comparison ; for man's structure, except his brain, is far less modified than that of many animals. Note, then, the following points : 1. The collar-bone (clavicle) is associated with wide separation of the shoul- ders, and the free use of the fore-limb for prehension or 90 EVIDENCES OF THE TFwUTH OF EYOLUTIOK for flight, but is gradually lost in proportion as the fore- limb is brought nearer together and used for suj^port. because it is no longer wanted. I say gradually, for all the steps of the passing away may be found. The use- less rudimentary condition is not uncommon. PROOFS FROM HOMOLOGIES. 97 2. The coracoid (c), it is seen, is a small, beak-like process of the blade-bone (scapula) in man and mam- mals ; but in birds (Fig. 11) and reptiles (Figs. 14, 18) •^cc^ Fig. 10. Fig. 11. Fig. 12. Fig. 13. Figs. 10-13. — 10. Fore-limb of bat. 11. Bird. 12. Archseopteryx. 13. Pterodactyl. (Lettered as in previous figures ; grouped from various sources.) it is a separate bone as large as the blade-bone itself, jointed with the latter at the shoulder and with the breast-bone (sternum) in front, thus making together a strong shoulder-girdle for the attachment of the fore- limb. This was undoubtedly the condition in the origi- nal or earliest walking animal, viz., reptiles. It was inherited and retained by birds, because necessary for powerful action of the wings in flight. In mammals it gradually dwindled and became united with the blade- bone as a process. In one mammal, the lowest and most 98 EVIDENCES OF THE TRUTH OF EVOLUTIOK reptilian living — the ornithorliynclius — tlie coracoid is much like that of re|)tiles — a large, flat bone, separated from the blade-bone and articulated with the breast- FiG. 14. Fig. 15. Fiu. 16. Fig. 17. Figs. 14-17.— 14. Fore-limb of turtle. 15. Mole. 16. Whale. 17. Fish. bone. It is a significant fact that, in the mammalian embryo, it is first developed as a separate bone and afterward united with the scapula. 3. In man, monkeys, bears, and some other mam- mals, the limb is fairly free from the body and the el- bow half-way down the limb ; while in herbivores (Figs. 8, 9), such as the horse, ox, and deer, etc., the elbow is high on the side of the body, and the limb is free only from the elbow downward. Perhaps in these cases most observers do not recognize it as an elbow at all. All gradations between these extremes are easily traced. The free condition of the limb is evidently the original one, the condition in herbivores being an extreme modi- PEOOFS FROM HOMOLOGIES. 99 fication associated with another modification mentioned under 5. 4. In man and in many mammals, and in all reptiles and birds, there are two bones in the forearm (radius and ulna). In the more spe- cialized forms of hoofed animals (ungulates), such as horse and ruminants (Figs. 8, 9), there is apparently but one. Two is the normal and original number ; but one of them, the ulna, has gradually become smaller and smaller, and finally is reduced to a short splint, and consoli- dated with the radius as a pro- cess extending backward to form the j)oint of the elbow. In the horse family every step of this reduction and consolidation may be traced in the course of its geological history. 5. The ivrist of many mam- mals and all birds differs in structure from that of man, chiefiy in containing a smaller number of bones. The normal number, as in man, seems to be eight. The decrease takes place mainly by consolidation of two or more into one. In such 100 EVIDENCES OF THE TRUTH OF EVOLUTION. cases usually the embryo will show the bones still separate, thus revealing the ancestral condition. Again, the posi- tion of the wrist is noteworthy. In man, monkeys, the bear family, and several other mammalian families, and in all reptiles, the hand bends forward at the wrist, so that the tread is on the w^hole palm (palmigrade). But, in all the most specialized mammals, the wrist can not bend in this direction, and therefore this joint can not be brought to the ground. The tread is therefore on the toes (digitigrade), and the wrist is high up above the ground. In the horse (Fig. 9), the ox, and many other mammals, for example, the wrist is so high that it is not usually recognized as a wrist, and is often called the fore-hnee. ISTow, homologous parts ought to have the same scientific name; but to use the word '^liand^^ in the case of lower animals might produce confusion and misconception. Therefore it has been agreed among comparative anatomists to use instead the Latin word ^^7nanus" for all that corresponds, in any animal, to the hand of man — i. e., all from the wrist downward. The manus of a horse is about fifteen inches long. The manus of a pterodactyl, such as that found by Marsh in the cretaceous strata of the West, with an expanse of wings of twenty-five feet, wa^ probably not less than seven or eight feet long. 6. The number of palm-bones (metapodal) and toes deserves special notice. In fishes, and in some extinct swimming reptiles, these are or were very numerous, but in the earliest land-aninials they became five. This is PEOOFS FEOM HOMOLOGIES. 101 the number now in nearly all reptiles, and in all the more generalized mammals. It may be called the normal number for a walking animal. In very many mammals, such, for example, as the dog family, they are reduced to four, though the fifth often remains as a useless, rudi- mentary splint and dew-claw (Fig. 6), thus showing the process of dwindling in the ancestry. In hoofed ani- mals the process of gradual diminution is shown even in existing forms, and still better in extinct forms. Confining ourselves, now, only to existing forms, in the elephant there are five palm-bones and toes, and in the hippopotamus there are four, all functional. In the hog (Fig. 7) there are still four, but two are behind the others and much smaller, and do not touch the ground — are not functional unless in soft ground. In the cow, deer, etc., the palm-bones are reduced to two, and these are consolidated into 07ie (canon-bone), and the toes are reduced to two eflScient and two useless rudiments. In the sheep and the goat (Fig. 8) these useless rudiments are dropped, and there are two only. Finally, in the horse (Fig. 9), the toes are reduced to one, although the palm-bones are still three, two of them, however, being reduced to rudimentary splints. How is it with birds ? Have these also palm-bones and fingers ? Yes, in birds (Fig. 11) there are three palm-bones and three fingers (the fourth and fifth being wanting) ; one of them — the thumb — is free, and some- times carries a claw. In the earliest known and most reptilian bird, the archasopteryx (Fig. 12), all the three 102 EVIDENCES OF THE TRUTH OF EVOLUTION. fingers are free, have the full number of joints, and all of them carry claws. In the embryo of living birds the fingers are all free, as in the archseoj^teryx. 7. Observe, finally, as an admirable- illus- tration of different adaptative modifica- tions for the same pur- pose — flight — the structure of the manus of flying animals. In the bat (Fig. 10), the flat flying - plane is made by enormous elongation of the palm- bones and finger-bones, their wide separation and the stretching of a thin membrane be- tween them. In the pterosaurs, or extinct flying reptiles (Fig. 13), one finger only is greatly eularged and elongated, and the flyiug-membrane is stretched between it and the hind-leg (Fig. 19), while the other three fingers are free and provided with claws. If it be asked which finger is it that is so greatly enlarged in this animal, PROOFS FROM HOMOLOGIES. 103 we answer, it is the little finger. In birds, on the con- trary, the manus is consolidated to the last dec'ree, to form a strong basis for attachments for the quills which form the flying-plane, and which are themselves extreme modiflcations of the scales of reptiles. But throughout all these extreme modifications the same essential struct- ure is detectable. It is perhaps unnecessary to dwell upon the still greater modifications of limbs for swimming, as in the whale (Fig. 16), the ichthyosaur, mosasaur (Fig. 18), and the fish (Fig. 17). A careful inspection of the figures, after what we have said, will be sufficient to explain them. In the fish alone the upper segments of the limb, viz., shoulder-girdle and humerus, are want- ing, not being yet introduced, and the manus is not yet differentiated into palm-bones and fingers, and the fingers are indefinitely multiplied. All these characters are indications of low position in the scale of evolu- tion. The earliest vertebrates were fishes. Limbs were not yet completely formed. In embryos of higher ani- mals, also, the outer segments are first formed. Hind-Limbs. — Figs. 20 to 24 represent, in a similar way, the hind-limbs of several animals — in this case all mammals. As before, corresponding parts are similarly lettered, and a dotted line is carried through certain prominent parts, especially the knee, heel, instep, and toes. By careful inspection the figures explain them- selves. Nevertheless, it will be well to draw special at- tention to several of the more important points : 104 EVIDENCES OF THE TEUTH OF EVOLUTION". 1. See, then, the j)ositioii of the knee. The thigh- bone in man, monkeys, bears, and several other families of mammals, and all reptiles, is free from the body, and PROOFS FROM HOMOLOGIES. 105 the knee is far removed and half-way down the limb (Figs. 20, 21). This is undoubtedly the original and normal condition of land-animals. But in all the more highly s^Decialized and swifter animals the knee is brought nearer and nearer to the body, until, in the swiftest of all, such as the ruminants and the horse (Figs. 23, 24), it is high up on the side of the body, in the middle of what is usually called the thigh but which really includes the thigh and the upper part of the lower leg or shank, 2. See, again, the position of the heel. In man, monkey, bear, and many other mammals, and all living reptiles, the heel is on the ground, the tread is on the whole foot, plantigrade ; while in all the more special- ized and agile animals, and especially in the swiftest of all, such as the horse, the deer, etc., the heel is high in the air, and the tread is digitigrade. 3. Observe, again : there are two degrees of digiti- gradeness. The one we find in carnivorous or clawed digitigrades, the other in herbivores or hoofed digiti- grades. In the one the tread is on the whole length of the toes to the balls, as in man when he tip-toes; in the other the tread is on the tip of the last joint alone. All that in any animal corresponds to the foot of a man — i. e., from the hamstring and heel downward — is called, in comparative anatomy, the ^^ pes.^^ The pes, or foot of a horse, is eighteen inches long. It is easy to see what spring and activity this mode of treading gives to an animal. Think how helpless a horse would be if he trod on the whole foot, heel down ! 106 EVIDENCES OF THE TRUTH OF EVOLUTION. 4. Observe, again, the number of toes. In the pro- cess of specialization there is a tendency for these to become fewer and stronger.* The normal number, as already seen, is five. All the earliest mammals, and many orders of mammals still living, have five ; but in the most specialized orders, such as the ungulates or hoofed animals, they were steadily reduced in number in the course of evolution. In the elephant there are still five, in the hippopotamus there are four, in the rhinoce- ros three, in the goat two, in the horse one. Still more the order of the dropping is regular. If an animal have but four toes, it is usually the first, or great toe, or thumb, that is wanting, or may be rudimentar}^ * This is only oue example under a general law which it may be well to stop a moment to illustrate. A repetition of similar parts per- forming the same function is always an evidence of low organization, and as we rise in the scale of organization such parts usually become fewer and more efficient. Thus, to give one example, myriapods, as their name indicates, have hundreds of locomotive organs — lower crustaceans perhaps thirty or forty. As we go up, they are reduced to fourteen (tct- radecapods), then to ten (decapods), then in spiders to eight, in insects to six, in vertebrates to four, and in man to two. A similar reduction in number, but increase in efficiency, is found in toes, when they are used for support and locomotion only. In man we find the normal number of five (1), because his hands are used for grasping and the functions of the fingers are not the same ; and (2), because man's development was almost wholly hrainioard. In other respects his structure is far less specialized than most other mammals. He can not compete with carnivores in strength and ferocity, nor with herbivores in fleetness. In the struggle for life, therefore, there was nothing left for him but increase in intelli- gence. Probably four is the smallest number of locomotive organs con- sistent with highest efficiency. In retaining but two legs for locomotion, man has lost in locomotive efficiency, but by the sacrifice he liberates two limbs for higher functions. PROOFS FROM HOMOLOGIES. 107 If, as in the rhinoceros, there are only three, then No. 5, or little toe, is also wanting, and the existing toes are Nos. 2, 3, and 4. If an animal has only two toes, as the goat, these are Nos. 3 and 4; and if only one, as the horse, it is the third or middle toe. Or, to put it more definitely : hoofed animals are divided into two groups, even-toed (artiodactyl) and odd-toed (perisso- dactyl). The even-toed may have four, as in the hip- popotamus ; or two, as in the goat. The odd-toed may have three, as in the rhinoceros ; or but one, as in the horse. Now, both of these orders came by dif- ferentiation, far back in the Eocene Tertiary, from a five-toed plantigrade ancestor. After dropping No. 1 (thumb or great toe) it is not yet decided, so far as num- ber of toes is concerned, whether the resulting four-toed animal shall become artiodactyl or perissodactyl. If the former, then the two side-toes (Nos. 2 and 5) become shortened up, as in the hog ; then rudimentary, as in the ox and deer ; and finally pass away entirely, as in the goat. If, on the other hand, the four-toed animal is on the line of perissodactyl evolution, it becomes first a three-toed animal by dropping No. 5. Now, the two side- toes (Nos. 2 and 4) shorten up more and more, and the middle toe increases in size, until finally, in the modern horse, only the greatly enlarged middle toe (No. 3) re- mains. We look with wonder and admiration at the danseuse pirouetting on the point of one toe. The horse is performing this feat all the time. Yes, the one toe of a horse has all the three joints like ours. 108 EVIDENCES OF THE TRUTH OF EVOLUTION. The coffin-bone is the last joint, and the hoof is the naiL Genesis of the Horse. — Every step of this process on the perissodactyl line may be traced in the history of the genesis of the horse. The beautiful form and struct- ure of this animal were not made at once, but by a slow process of integration of small changes from generation to generation, and from epoch to epoch of the earth's history. The horse (as in fact did all ungulates) came from a five-toed plantigrade ancestor, but we are not able to trace the direct line of genesis quite so far. The earliest stage that we can trace with certainty, in this line of descent, is found in the eohippus of Marsh. This was a small animal, no bigger than a fox, with three toes behind and four serviceable toes in front, with an ad- ditional fifth palm-bone (splint), and perhaps a rudi- mentary fifth toe like a dew-claw. This was in early Eocene times. Then, m later Eocene, came the orohip- pus, which differs from the last chiefly in the disappear- ance of the rudimentary fifth toe and splint. (See Fig. 25.) Next, in the Miocene, came the mesohippus and miohippus. These were larger animals (about the size of a sheep), and had three serviceable toes all around ; but in the former the rudiment of a fourth splint in the fore- limb yet remained. Then, in the Miocene, came the pro- tohippus and pliohippus. These were still larger ani- mals, being about the size of an ass. In the former the two side-toes were shortening up and the middle toe becom- ing larger. In the latter the two side-toes have become Equus : Qua- ternary and Recent. Pliohippus : Pliocene. Protohippus ; Lower Plio- cene. JJiohippus ; Miocene. Mesohippus : Lower Mio- cene. Orohippus Eocene. PROOFS FEOM HOMOLOGIES. d Fig. 25. — Diagram illustrating gradual changes in the horse family. Throughout a is fore-foot ; '6, hinci-foot ; c, fore-arra ; d, shank ; e, molar on side-view ; / and y, grinding surface of upper and lower molars (after Marsh j. 110 EVIDENCES OF THE TRUTH OF EVOLUTION. splints. Lastly, only in the Quaternary conies the genus Equus, or true horse. The size of the animal is become greater, the middle toe stronger, the side-splints smaller ; but in the side-splints of tlie modern horse we have still remaining the evidence of its three-toed ancestor. Similar gradual changes may be traced in the two leg-bones, which have gradually consolidated into one ; in the teeth, which have become progressively longer and more complex in structure, and therefore a better grind- er ; in the position of the heel and wrist, which have become higher above-ground ; in the general form, which has become more graceful and agile ; and, lastly, in the brain, which has become progressively larger and more complex in its convolutions — to give greater battery- power, to make a more powerful dynamo — to work the improved skeletal machine. See, then, how long it has taken ISature to produce that beautiful finished article we call the horse ! We have taken only limbs as examples of what is true of the whole skeleton. To the superficial observer the bodies of animals of different classes seem to differ fun- damentally in plan — to be entirely different machines, made each for its own j)i^rposes, at once, out of hand. Extensive comparison, on the contrary, show^s them to be the same, although the essential identity is obscured by adaptive modifications. The simplest, in fact the only scientific, exiDlanation of the phenomena of verte- brate structure is the idea of a primal vertebrate, modi- PROOFS FROM HOMOLOGIES. m fied more and more through successive generations by the necessities of i^ifferent modes of life. See, then, in conclusion, the difference between man's mode of working and Nature's. A man having made a steam-engine, and desiring to use it for a different pur- pose from that for which it was first designed and used, will nearly always be compelled to add new parts not contemplated in the original machine. Nature rarely makes new parts — never, if she can avoid it — but, on the contrary, adapts an old part to the new function. It is as if Nature were not free to use any and every device to accomplish her end, but were conditioned by her own plans of structure ; as, indeed, she must be according to the derivation theory. For example : In early Devonian times fishes were the only representatives of the verte- brate type of structure. The vertebrate machine was then a swimming -machine. In the course of time, when all was ready and conditions were favorable, reptiles were introduced. Here, then, is a new function — that of lo- comotion on land. We want a wallcing-macliine. Shall we have a new organ for this new function ? No : the old swimming-organ is modified so as to adapt it for walking. Time went on, until the middle Jurassic, and birds were introduced. Here is a new and wonderful function, that of flying in the air. We want a flying- machine. We know how man would have done this ; for we have the result of his imagination in angels of Chris- tian art and griffins of Greek mythology. He would have added wings to already existing loarts, and this 112 EVIDENCES OF THE TRUTH OF EVOLUTION. would have necessitated the alteration of the whole plan of structure, both skeletal and muscular. Nature only modifies the fore-limbs for this new purpose. If we must have wings, we must sacrifice fore-legs. We can not have both without violating the laws of morphology. Finally, ages again passed, and, when time was fully ri^oe, man was introduced. Now we want some part to per- form a new and stiU more wonderful function. We want a hand, the willing and efficient servant of a rational mind. We know, again, how man would have done this, for we have the result in the centaurs of Greek mytholo- gy, in which man's chest, and arms, and head are added to the body of a quadruped. But natural laws must not be violated, even for man. If we want hands, we must sacrifice feet. Again, therefore, the fore-limbs are modi- fied for this new and exquisite function. Thus, in the fin of a fish, the fore-paw of a reptile or a mammal, the wing of a bird, and the arm and hand of a man, we have the same part, variously modified for many purjDoses. Many other illustrations might be taken from the skeleton and from other systems, especially the muscular and nervous. But in the muscular svstem the modifica- ft/ tions have been so extreme that homology is much more difficult to trace, and therefore requires more extensive knowledge than we yet possess, and more extended com- parison than has yet been attempted. It has been traced with some success through mammals, and probably will be through air-breathing vertebrates — i. e., also through birds, reptiles, and amphibians ; but to trace it through PROOFS FROM HOMOLOGIES. 113 fishes seems almost hopeless. In the case of the nervous system, and especially of the brain, it is again distinct ; but this had better be taken up under another head, yiz., proofs from ontogeny. Chapter VI. In the visceral organs homology is very plain, in fact too plain. There is not modification enough in most cases even to obscure it, because function is the same in all animals. These organs do not, therefore, furnish good illustrations of that essential identity in the midst of adaptive modification which constitutes the argument for the derivative origin of structure. It is the organs of animal life that show this most perfectly, because it is these that take hold on the environment and are modified by it. There are, however, a few striking illus- trations to be found among the visceral organs, especially the blood-system. This, however, had better also be deferred to the chapter on ontogeny. CHAPTER V. HOMOLOGIES OF THE ARTICULATE SKELETON. We have taken the vertebrate skeleton first, only be- cause this department is most familiar. But in reality, the most beautiful illustrations of essential identity of structure in the midst of infinite diversity of adaptive modification for different functions and habits of life, and therefore of common origin from a primal form, are found in the department of articulates. I use the old Cavierian department articulata, rather than the more modern arthropods^ because the former includes worms also. Now, whether worms should be thus included with arthropods, or deserve a whole department to themselves it matters not for our purposes. It is generally admitted that arthropods probably descended from marine worms. They all have the same general plan of skeletal structure. It will suit my purpose, therefore, to regard worms as the lowest form of jointed animals. Here, then, we have an entirely different plan of structure — a different style of architecture and different mechanical principles of machinery. Instead of a skele- ton within and muscles acting on the outside, we have HOMOLOGIES OF THE ARTICULATE SKELETON. 115 the skeleton on the outside, and muscles acting from within. Instead of two cavities, a neural and visceral, the skeleton forms but one cavity, in which all organs are inclosed and protected. Instead of finding the nerve-axis on the dorsal aspect of the body, we find it on the ventral aspect. Take any articulate animal, for example, a shrimp, a cenfciped, or a beetle. Cut it across the body, and look at the end (Fig. 26). We see a ring of bone (chitin) in- FiG. 26. — Diagram section across an arthropod, showing the inclosing skeleton-ring and a pair of jointed appendages, n, nervous center ; V, viscera ; b, blood system. closing all the organs (nervous system n, blood system b, and visceral system v), and a pair of jointed appendages, perhaps legs, on each side. Now imagine these parts repeated in a linear series. The rings repeated make a hollow, jointed tube or barrel, the appendages repeated make a continuous row of appendages on each side. Now 116 EVIDENCES OF THE TRUTH OF EVOLUTION. this is exactly what we actually find. The whole articu- late skeleton is ideally made up of a series of such re- peated rings and a23pendages, modified according to the l^osition in the series, and the uses to which they are put. And then the whole articulate department is made up of such articulate animals again modified according to place in the scale of articulates. The modification in the lower forms is slight, and therefore the identity of the repeated parts is obvious ; but as we go up the scale, and the number and complexity of the functions in- crease, the adaptive modification becomes greater and greater, until finally it so obscures the essential identity, that it requires the most extensive comparison in the taxonomic series and in the ontogenic scries, to pick up the intermediate links and establish the fact of common origin. In a word, whether they so originated or not, it is certain that the structure of articulate animals is ex- actly such as would be the case if all these animals were genetically connected, and came originally from a primal form something like one of the lower crustaceans, or, perhaps, a marine worm. It will be best to take an example from about the middle of the scale, where the two elements, viz., essen- tial identity and adajotive modification, are somewhat evenly balanced, and both traceable with ease and cer- tainty. Take, then, a cray-fish, a lobster, or a shrimp. This animal (Fig. 27) has twenty or twenty-one rings and pairs of jointed appendages. The rings are some of them diminished, some of them increased in size. HOMOLOGIES OF THE ARTICULATE SKELETON. 117 Fig. 27. — Shrimp (Palaemonetes vulgaris). Sometimes several are consolidated ; sometimes several are partially or wholly aborted. The appeadages are modified in shape and size, according to their position, so as to make them s^yimming-appen- dages (swimmerets), walking - appendages (legs), eating-append- ages (jaws), and sense- appendages (antennas). For example, in the abdomi- nal region, or so-called tail, we have seven segments, all being perfect movable rings, each with its pair of jointed appendages, except the last, or telson. The appendages of the first ring (Fig. 28, B) are specially modified in the male as organs of copulation (B'). The next four pairs are modified for swimmerets (D') and for use as holders of the eggs in the female. The ap- pendages of the sixth ring (G) are broad and paddle- shaped, and, together with the telson or seventh ring (H), form the powerful terminal swimmer. Going, now, to the cephalo-thorax : in this either a large num- ber of segments (thirteen or fourteen) are consolidated above to form the upper shell or carapace ; or else, as is more probable, two or three of the anterior seg- ments have enlarged and grown backward over, and at the expense of the others, to form this shell. At any rate, it is certain that the carapace is formed of the dorsal portions of a number of segments consolidated Fig. 28. — External anatomy of the lobster (after Kingsley). HOMOLOGIES OF THE ARTICULATE SKELETON. 119 together. Below, however, the seg- ments are all dis- tinct, and have each its own pair of appendages. For example, go- ing forward in this region, the five next -pnh's of appendages are greatly enlarged and very strong, and serve the pur- pose of locomo- tion. They are icalMng - append- ages. The next two or three pairs are smaller and somewhat modi- fied, but not so much as to ob- scure their essen- tial similarity to legs. Like legs, they are many- jointed, and like legs, too, they 13 Oi Dt C5 '^J'^^TTVa 120 EVIDENCES OF THE TRUTH OF EVOLUTION. have gills attached to them. Thej are called maxilli- peds, or jaw-feet. They are used like hands to gather food and carry it to the mouth. They are gatliering- cqjpendages. Then follow three or four pairs still more modified^ and used for mastication. They are called maxillae and mandibles. They are eating -appendages. Then follow two pairs, long, man3'-jointed, with the same kind of curious hinge-joints, which we have in the legs, undoubtedly homologous with all the others, but used for an entirely different purjoose, and special- ly modified for that purpose. They are the antennas. They are delicate organs of touch and of hearing, for Fig. 31. — Vibilia, an arnpliibod crustacean (after Milne Edwards). the ear is situated in the basal joint of the ar.terior pair. Last of all, there is still another pair, jointed and movable, on the ends of which are situated the eyes. These last three, therefore, are sense-appendages. Some HOMOLOGIES OF THE ARTICULATE SKELETON. 121 writers make this last pair special organs, not homolo- gous with appendages. For the sake of greater distinctness, we give the whole series of these appendages in one of the higher forms, viz., the prawn (Palemon, Fig. 29, and in one of the lower forms, Nebalia, Fig. 30). Fig. 82. — Lithobius forclpatus (after Carpenter). That these are really homologous parts is further shown by the fact that in the case of other crustaceans, such as limulus, the same appendages, i. e., the append- ages of the same body segments, which in the cases be- fore mentioned are used as feet, become swimmers, while the appendages corresponding to jaw-feet become walk- ers ; and even what corresponds to antennae or sense- appendages, may, as in branchippus, become powerful claspers. Finally, in all the lowest crustaceans, the identity is evident, because all the segments and their appendages are much alike in form and function (Fig. 31). We have taken exaaiples from near the middle of the articulate scale, because, as already stated, both the essen- tial identity and the adaptive modifications are easily 122 EVIDENCES OF THE TRUTH OF EVOLUTION". traced. If we go downward in the scale, the structure becomes more and more generalized, and the rings and appendages become more and more alike (Fig. 31), until in the most generalized forms we have only a series of similar rings, with similar pairs of appendages, except some necessary modifications to form the head and tail. This is well shown in the centiped (Fig. 32), and still better in marine worms (Fig. 33). In some marine worms the slight modification to form the head takes Fig. 33. — Syllis prolifera. place under our very eyes. These often multiply by di- viding themselves into two. When they do so, they make a new head and new tail by slight modification of seg- ments and appendages (Fig. 33). If, on the other hand, we go up the scale, we find adaptive modifications obscuring more and more the simple and obvious identity of parts, until finally the identity can not be recognized without extensive com- parison in the taxonomic series and study of embryonic conditions. In crabs— which is a higher form than cray- fisli — the tail or abdomen seems to be wanting, but is only very sijpiall and bent under the body and thus concealed. In all essential respects the structure is precisely like the HOMOLOGIES OF THE ARTICULATE SKELETON. 123 cray-fish. In fact, in the embryo, we trace the one form into the other ; for the crab is at first a long-tailed crus- tacean (Fig. 34). Insects are the highest form of articulates. In these, therefore, we find the modification is still greater than in Fig. 34. — Development of Carcinus moenas. a, zosea stage ; b, megalopa stage ; c, final state (after Couch). crustaceans, though even here the ring-and-appendage structure is plain enough in most cases. One of the best evidences of high grade among ani- mals is the gathering of the segments into distinct groups, and especially the distinctness of the head as one of these groups. In worms and lower crustaceans there is no grouping at all, the skeleton being a continuous series of joints, only slightly modified at the anterior and posterior extremities. In the higher Crustacea, and in spiders and scorpions, they are grouped into two 124 EVIDENCES OF THE TRUTH OF EVOLUTION. Gjvt&ivn^ Tarsus^s^ Talmas -« C"\ ^rotVvova)C. J) / ^A^ ScuUVlum .(^ Steymle. ^ U.p. ^ Fig. 35. — External anatomy of Caloptenus spretus, the head and thorax disjointed ; up, uiopatagium ; /, furcula ; c, cercus (drawn by J. T. Kingsley). HOMOLOGIES OF THE ARTICULATE SKELETON. 125 regions, viz., cephalo-thoras and abdomen. In insects they arc grouped into three yery distinct regions — head, thorax, and abdomen. In insects, therefore, we find for the first time the head distinctly separated from the rest of the body. This is an evidence of high grade, because it shows the dominance of head-functions. The insect, such, for example, as a grasshopper, con- sists of seventeen or eighteen segments (Fig. 35). Of these, four belong to the head, three to the thorax, and about ten to the abdomen. Those of the abdomen are all separated and movable ; those of the thorax and head are more or less consolidated. The appendages of the head-segments become antennse and jaw-parts, 1. e., mandi- bles — maxilla and labium ; the appendages of the thorac- segments become legs (the wings are not homologous with appendages), while those of the abdomen are aborted. The steps of the gradual consolidation on the one hand, and the abortion on the other, mav be traced in the em- bryo or larva — i. e., in the caterpillar or the grub of a bee or a beetle. In the caterpillar, for example, there is no grouping into three regions, there is no consolida- tion, and all the segments have appendages. Again, the almost infinite variety in the mouth-parts among in- sects, brought about by adaptive modifications for biting, for piercing, and for sucking, and yet the essential iden- tity of all to the more simple and generalized structure of the grasshopper, is an admirable illustration of the same principle. But to dwell upon these minor points would carry us too far. 126 EVIDENCES OF THE TRUTH OF EVOLUTION. Illustration of the Law of Differentiation.— We have here, in the modifications of segments and appendages of articulates, an admirable illustration of the most funda- mental law of evolution, viz., the law of differentiation. As we have already seen (page 21), perhaps the most beautiful and certainly the most fundamental illustra- tion of this law is found in the development of cell- structure. Commencing in the lowest animals, and in the earliest embryonic stages of the higher animals, from a condition in which all are alike, the cells as w^e go upward quickly diverge into different forms to pro- duce different tissues and perform different functions. Here, then, we have a perfect example of essential iden- tity and adaptive modification. It is the very best type of differentiation. So also skeletal segments, commenc- ing, in the lowest articulates and in earliest embryonic stages of the higher, all alike, as we go upward in either series, begin immediately to diverge in various directions (divergent variation), taking different forms to subserve different uses. Here, again, therefore, is an illustration of the law of differentiation. Lastly, in the articulate department, commencing with the lowest forms and earli- est embryonic conditions, and we may add earliest geo- logical times, and going up either series from generalized forms very much alike, the individuals are gradually differentiated into many special forms, in order to adapt them to the diversified modes of life actually found in nature. Thus cells, segments, individuals, are all alike affected by this most fundamental law. HOMOLOGIES OF THE ARTICULATE SKELETON. 127 We have taken our illustrations from only the two de- partments of vertebrata and articulata, because these are the most familiar to the reader, and also have been most carefully studied. We have shown that the general structure of all vertebrates is precisely what it would be if they all had come from one primal vertebrate form, and that of all articulates what it would be if all had come from one primal articulate form. The only natural ex- planation, and, therefore, the only scientific explanation of this, is that they loere really thus derived. The same kind of evidence may be drawn from the study of other departments, but to pursue the subject any further in this direction would carry us beyond the limits which we have assigned. We desire only to explain the nature, not to give all, of the evidence. The examples given will be sufficient for the purposes of illustration. The whole proof is nothing less than the whole science of compara- tive anatomy. Vertebrates, then, were derived from a primal verte- brate, articulates from a primal articulate, and so for other departments. But whence were these jormcf/^ derived ? Are there any intermediate links between, any deeply concealed common plan of structure underlying these primary groups, showing a common origin ? It must be confessed that, in their mature condition, there seems to be but little evidence of such. These .primary groups seem to be built on different plans, to be fundamentally of different styles of architecture. Therefore Darwin, in the true spirit of inductive caution — that true scientific 7 128 EVIDENCES OF THE TRUTH OF EVOLUTION spirit which keeps strictly within the limits of evidence — commences with four or five distinct primal kinds, from which by divergent variation all animals were de- scended. Nevertheless, the truly scientific biologist must ever strongly incline to believe that these also came from some yrimdl animal, and even that both animals and plants were derived from some primal form of living tiling ; that as, in the taxonomic series, the animal and vegetal kingdoms in their lowest forms merge undistinguishably into one another; as in the ontogenic series the animal and plant germ are one, so also in the phylogenic series the earliest organisms were simply living things, but not distinctively ani- mal nor vegetal. Science, therefore, whose mission is to trace origins as far back as possible, must ever strive to find connecting links between the primary groups. Some such have been supposed to have been discovered. Some find the origin of vertebrates among the molluscoids (as- cidians) ; some find the origins of both vertebrates and articulates among marine worms (annelids). This point is still too doubtful to be dwelt upon here. It may be that we seek in vain for such connecting links among existing forms. It may well be that the point of separa- tion of these great primary groups (unless we except vertebrates) was far lower even than these low forms. Both phylogeny and ontogeny seem to indicate this. In the earliest fauna known, the primordial (for if there was life in the archaean it was not yet differentiated into a fauna), all the great departments, except the vertebrates. HOMOLOGIES OF THE AETICULATE SKELETOiT. 129 seem to have been represented. In embryonic develop- ment, too, the point of connection or even of similarity, between the great departments, is found, as we shall see hereafter, only in the earliest stages — i. e., lower down than any but the lowest existing forms, viz., the pro- tozoa. CHAPTER YI. PKOOFS FKOM EMBRYOLOGY, OR COMPARISOi^ li^ THE ONTOGEJTIC SERIES. It is a curious and most significant fact that the suc- cessive stages of the development of the indiviclttal in the higher forms of any group (ontogenic series) resemble the stages of increasing complexity of differentiated structure in ascending the animal scale in that group (taxonomic series), and especially the forms and structure of animals of that group in successive geological epochs (phylogenic series). In other words, the individual higher animal in embryonic development passes through temporary stages, which are similar in many respects to permanent or mature conditions in some of the lower forms in the same group. To give one example for the sake of clearness : The frog, in its early stages of embry- onic development, is essentially a fish, and if it stopped at this stage would be so called and classed. But it does not stop ; for this is a temporary stage, not a permanent condition. It passes through the fish stage and through several other temporary stages, which we shall explain hereafter, and onward to the highest condition attained PROOFS FROM EMBRYOLOGY. 131 by amphibians. Now, if we could trace perfectly the successive forms of amphibians, back through the geo- logical epochs to their origin in the Carboniferous, the resemblance of this series to the stages of the deyelop- ment of a frog would doubtless be still closer. Surely this fact, if it be a fact, is wholly inexplicable except by the theory of derivation or evolution. The embryo of a higher animal of any group passes now through stages represented by lower forms, because in its evolution (phy- logeny) its ancestors did actiudly have these forms. From this point of view the ontogenic series (individual his- tory) is a brief recapitulation, as it were, from memory, of the main points of the philogenic series, or family his- tory. We say brief recapitulation of the main points, because many minor points are dropped out. Even some main points of the earliest stages of the family history may be dropped out of this sort of inherited memory. This resemblance between the three series must not, however, be exaggerated. Not only are many steps of phylogeny, especially in its early stages, dropped out in the ontogeny, but, of course, many adaptive modifica- tions for the peculiar conditions of embryonic life are added. But it is remarkable how even these — for exam- ple the umbilical cord and placenta of the mammalian embryo — are often only modifications of egg-organs of lower animals, and not wholly new additions. It is the similarity in spite of adaptive modifications that shows the family history. We will now illustrate by a few striking examples. 132 EVIDENCES OF THE TRUTH OF EVOLUTION". We can not do better than to take, again, as our first example, the development of tailless amphibians, and dwell a little more upon it : 1. Ontogeny of Tailless Amphibians.— It is well known that the embryo or larva of a frog or toad, when first hatched, is a legless, tail-swimming, water-breathing, gill-breathing animal. It is essentially a fish, and would be so classed if it remained in this condition. The fish retains permanently this form, but the frog passes on. Next, it forms first one pair and then another pair of legs ; and meanwhile it begins to breathe also by lungs. At this stage it breathes equally by lungs and by gills, i. e., both air and water. Now, the lower forms of am- phibians, such as siredon, menobranchus, siren, etc., re- tain permanently this form, and are therefore called perennibranchs, but the frog still passes on. Then the gills gradually dry up as the lungs develop, and they now breathe wholly by lungs, but still retain the tail. Now this is the permanent, mature condition of many amj^hi- bians, such as the triton, the salamander, etc., which are therefore called cadiicihranclis, but the frog still passes on. Finally, it loses the tail, or rather its tail is absorbed and its material used in further development, and it becomes a perfect frog, the highest order (ajioura) of this class. Thus, then, in ontogeny the fish goes no further than the fish stages. The perennibranch passes through the fish stage to the perennibranch amphibian. The caduci- branch takes first the fish-form, then the perennibranch- form^ and finally the caducibranch-form, but goes no PROOFS FROM EMBRYOLOGY. 133 further. Last, the anoura takes first the fish-form, then that of the perennibranch, then that of the caduci- branch, and finally becomes anoura. This is shown in the diagram, which must be read upward, line by line. FISH. PERENNIBRANCH. CADUCI BRANCH. ANOURA. FISH. PERENNIBRANCH. CADUCIBRANCH. FISH. PERENNIBRANCH. FISH. Diagram showing the stages of development of amphibians. (To be read upward.) Now, this is undoubtedly the order of succession of forms in geological times — i. e., in the phylogenic series. This series is indicated by the arrows in the diagram. Fishes first appeared in the Devonian and Upper Silurian in very reptilian or rather amphibian forms. Then in the Carboniferous, fishes still continuing, there appeared the lowest — i. e., most fish-like — forms of amphibians. These luere undouMedly perennihranclis. In the Per- mian and Triassic higher forms ajDpeared, which were cer- tainly caducibranch. Finally, only in the Tertiary, so far as we yet know, do the highest form (anoura) appear. The general similarity of the three series is complete. If we read the diagram horizontally, we have the onto- genic series ; if diagonally with the arrows, we have both the taxonomic and the phylogenic series. 2. Aortic Arches. — But some will, perhaps, say that these stages in the ontogeny are only examples of adapt- 131 EVIDENCES OF THE TRUTH OF EVOLUTION. ive modifications — like modifications for like conditions of life — and had better be accounted for in this way, without reference to family history. We will, therefore, take another example, which can not be thus accounted for — an example in which there is no possible use now for the peculiar form or structure which we find. For this purpose we take the case of the course of circu- lation in vertebrates. If one examines the large vessels going out from the Leart of a lizard, he will find six aortic arches — i. e., three on each side. These all unite below to form the one descending abdominal aorta. This is shown in the accompanying figure (Fig. 36), in which a a' a" and I V b" are the six arches. Now, there is no conceiva- ble use in having so many aortic arches. We know this, because there is but one in birds and mammals, and the circulation is as effective, nay, much more effective in these than in reptiles. The explanation of this anomaly is revealed at once as soon as we examine the circulation of a fish, Fig. 36. — Showing heart and out- going blood-vessels of a lizard (after Owen). The arrows show the course of the blood. PROOFS FROM EMBRYOLOGY. 135 which is shown in the accompanying figure (Fig. 37). The multiplication of the aortic arches is here, of A B Fig. o7. — a, heart and gill-arches of a fish ; b, one arch with fringe (after Owen) ; H, the heart. course, necessary, for they are the gill-arclies. The whole of the blood passes through these arches, to be aerated in the gill-fringes. The use of this peculiar structure is here obvious enough. If a lizard were eyer a fish, and afterward turned into a lizard, changing its gill-respiration for lung-respiration, then, of course, the useless gill-arches would remain to tell the story. Now, although a lizard never was a fish, in its individual his- tory or ontogeny, it was a fish in its family history or phylogeny, and therefore it yet retains, by heredity, this curious and useless structure as evidence of its ancestry. That this is the true explanation is demonstrated by the fact that in amphibians this very change actually 13G EVIDENCES OF THE TRUTH OF EVOLUTION. takes place before our eyes in the individual history. We have already seen that the individual frog, in its tadpole state, is a gill-breather. It has therefore its gill-arches Fig. 39. Figs. 38, 39, — Diagrams showing tlie change of the course of blood in the development of a frog. 38. The tadpole stage. 39. The mature condition, h, heart ; gg'g", external gills ; y^'^", internal gills; c c, connecting branches in the tadpole ; pp, pulmonary branches. PKOOFS FPwOM EMBRYOLOGY. I37 (Fig. 38), three on each side, like a fish, and for the same reason, yiz., the aeration of the blood. But when its gills dry up and lung-respiration is established, its now useless gill-arches still remain as aortic arches, to attest their previous condition (Fig. 39). Now, the lizard undoubt- edly came from an air-breathing, tailed ampliibian, and therefore inherited this form of arterial distribution. In both lizard and amphibian the ultimate cause is an origin from fishes, in which such arches are obyiously necessary. The diagrams. Figs. 38 and 39, are illustrations some- what idealized, showing the manner in which the change actually takes place in air-breathing amphibians. Fig. 38 represents the tadpole stage, and Fig. 39 the mature condition. In the former the gills are mostly external, GG', etc., but also internal, gg', as in the fish. Observe in this condition the small connecting vessels, cc'. When the external gills dry up, these are enlarged, and tlie whole of the blood passes through them, as shown in Fig. 39. It is seen, also, in Fig. 38, that a small branch, p, goes from the lower gill-arches to the yet rudimentary lung, /. When the gill-fringes have disappeared, the whole of the blood of the lower arch goes through the now enlarged pulmonary branch to the lungs, L, now in full activity, and the remainder of this arch disappears, as shown by the dotted lines in Fig. 39. The change which actually took place in the family history of the lizard probably differed from the above only in being more simple, the gills being only internal like the fish. The external gills complicate the process 138 EVIDENCES OF THE TRUTH OF EVOLUTION. a little in the case of the frog, but the principle is pre- cisely the same. As already explained (pages 82-85), the large gap be- tween fishes and reptiles, as regards mode of respira- tion, is completely filled both in the taxonomic series — i. e., in ganoids, dipnoi, and the mature condition of the different orders of amphibians — and in the ontogeny of the higher amphibians. Now, we add that the same is true of the arterial distribution. We have just traced the change in the ontogeny of the frog, but the steps of the same change are traceable in passing from the typical fish (teleosts), through dipnoi and amphibians to rep- tiles. Thus, again, the phylogeuy, the taxonomy, and the ontogeny, are in complete accord. But the argument for eyolution does not stop here. If birds and mammals have come from reptiles, and therefore from fishes, we may expect to find some evi- dences of the same kind still lingering in the great arter- ies. And such we do find. It is a most curious and significant fact that, in the early embryonic condition of birds and mammals, including man himself, we find on each side of the neck several gill-slits, each with its gill-arch, and therefore several aortic arches on each side, precisely similar to what we have already described. These arches are subsequently, some of them, obliterated ; some modified to form the one aortic arch, and some of them still more modified to form the other great arter- ies coming from the heart to supply the head and fore- limbs. PROOFS FROM EMBRYOLOGY. 139 This is so beautiful and convincing an example, and one so generally unfamiliar, to even intelligent persons. Fig. 40. — Diagram of mammalian heart, a, aorta ; p, pulmonary artery ; scs'c\ subclavium on each side ; €c\ carotids on each side. not especially acquainted with biology, that it is best to explain it more fully. In Fig. 40 we give a mammalian heart and outgoing vessels, very slightly modified, so as to suggest the process of change. In Fig. 41 we give an ideal diagram representing the primitive aortic arches as they exist in the embryo of mammals, birds, and reptiles. It represents, also, substantially, the arches as they exist in the mature condition in the most reptilian fishes (dipnoi) and in some sharks, except that in these 140 EVIDENCES OF THE TPwUTH OF EVOLUTIOIsr. the arches are of course furnished with gill-fringes. We will use this figure, therefore, to rej)resent both the em- FiG. 41. — Ideal diagram representing the primitive aortic arches (after Rathke). Fig. 42. — Modified for bird. bryonic condition of air-breathing vertebrates and the mature condition of some fishes. The place of the heart is indicated by the dotted circle. Fig. 36, on page 134:, shows what these arches become in reptiles (lizard). It is seen that the two upper arches on each side are obliterated, as indeed they already are in some teleost fishes. Fig. 42 shows what they become in birds. The two upper arches are, of course, obliterated. The others are all modified, each in a manner which may be readily understood by PROOFS FROM EMBRYOLOGY. Ml comparison with Fig. 41. Finally, Fig, 43 shows what they become in mammals and in man. In the bird (Fig. 42) the first pair of arches become the two pulmonary arteries as they do also in the lizard. The second pair become on the right side (left of the diagram) the aortic arch, on the left side (right of the diagram) the left subclavian, s'c' (the right subclavian, sc, is a branch of the aortic arch). The third pair become carotids, cc, while the fourth and fifth, as already said, are aborted. In the mam- mal (Fig. 43), on the left side (right of the dia- gram) the first arch be- comes the pulmonary artery, p. In the foetus the continuation of this arch forms the ductus arteriosus, which is afterward obliter- ated, as shown in the dotted line. The second arch be- comes the aortic arch, the third the left exterior carotid. On the right side (left of the diagram) the first arch becomes aborted ; the second, the right subclavian, sc (the left subclavian, s'c', is a branch of the aortic arch) ; and the third, the right carotid. Nos. 4 and 5, on both sides, as usual, are aborted. Fig. 43. — Modified for mammal. 142 EVIDENCES OF THE TRUTH OF EVOLUTION. d- ■711- V/^ See, then, the gradual process of change through tlie whole yertebrate department. In the lowest of all yer- tebrates, if vertebrate it may be called (for what corresponds to its backbone is an unjointed, fibrous cord), the am- phioxus or lancelet (Fig. 44), there are about forty gill-arches on each side. As we rise in the scale of fishes these are reduced in number. In the lam- prey, there are seven ; in the sliarks, usually five ; in ordinary fishes (tele- . osts), there are four or sometimes only three on each side, the others being aborted. Thus far the change is only by diminution of number in accordance with a law universal in biology, that decrease in the number of identical organs is evidence of advance in the grade of organization, provided that it be assoT3iated with more perfect struct- ure of the organ. The further change is one of adaptive modification. In some reptiles (lizard) the three gill- arches on each side all retain the form of aortic arches ; in some reptiles only Fig. 44. — Lancelet two retain this form. In birds and (Amphioxus Ian- . . ^ . ceoiatus). Mag- mammals only one arch is retained, in one-half Umes^^ ^^^^ form of aortic arch, the others be- PROOFS FEOM EMBRYOLOGY. I43 ing modified to form the great outgoing vessels of the heart, or else aborted. It mav be well to observe that in birds the one aortic arch turns to the right, while in mammals it turns to the left. This is positive evidence that mammals could not have come from birds, nor vice versa. They both came from reptiles, and, of the many reptilian arches, a right one was retained by the bird branch, and a left one by the mammalian. ■ In all the figures illustrating this subject, we have left out the great incoming vessels or veins, because we are not here concerned with them, they not being trans- formed gill-arches. Last of all, it may be well to stop a moment to show the cogency of this evidence. If it were a question of the origin of some structure not only useful (for all struct- ures selected by Nature must be useful) but the lest imaginable, like the" eye or the ear, for example ; then, if we examined only the liigliest form or the finished article, there are two ways in which it is possible to explain the adaptive structure. We may either suppose that it was made at once out of hand, by some intelligent contriver ; or else that it was slowly made by a process of evolution, becoming more and more perfect by a selection of only the most perfect from generation to generation. But in the case of the six aortic arches of the lizard, we are shut up to the one explanation only, viz., by slow process of evolution. One arch is all that is necessary, as is plainly shown by the use of only one in the more perfect circula- tion of birds and mammals. If the thing were done out U4: evide:nces of the truth of evolution of hand, unconditioned by the previous structure in fishes, to have made six was surely but a bungling piece of work. 3. Vertebrate Brain.— Another excellent example is the structure of the vertebrate brain. The brain of an average fish is represented in Fig. 45. It consists of four Fig. 45. — Fish-brain, a, side view ; b, top view. or five swellings, or ganglia, strung along, one beyond another. Commencing behind, these are, first, the me- dulla, m; then the cerebellum, cb ; then the optic lobes, ol ; then the cerebrum and thalamus combined, cr j and last, the olf active lobes, of. Of these, it will be observed, the optic lobe is the largest in the brain of the fish (Fig. 45). In the brain of the reptile (Fig. 46) we have the Fig. 46. — Reptile-brain, a, side view ; b, top view. same serial arrangement, of the same parts, only that the cerebrum has now become the dominant part instead of the optic lobes. In the average bird (Fig. 47) the cere- brum has grown so large that it extends backward, and partly covers the optic lobes. In the lower mammals (marsupials), the brain is much the same in this respect, PROOFS FROM EMBRYOLOGY. 145 as in birds — i. e., the cerebrum only partly covers the optic lobes, so that, looked at from above, the whole se- FiG. 47,— Bird-brain, a, side view • b, top view. ries of ganglia are still visible. But in the average mam- mal (Fig. 48) the cerebrum is so enlarged that it covers A B Fig. 48.— Mammal-brain, a, top view ; b, side view., entirely the optic lobes and encroaches on the cerebellum behind and the olfactive lobes in front. In some mon- keys, indeed, the cerebellum is nearly or even quite covered. Finally, in man (Fig. 49), the cerebrum has Fig. 49. — Man's brain, a, side view ; b, top view. 146 EVIDENCES OF THE TRUTH OF EVOLUTION. grown so enormously that it covers every other part and completely conceals them from view when the brain is looked at from above. In front it not only covers but r^yWOAV Fig. 50. — Ideal section showing all the above stages. has grown far bevond the olf active lobes : behind it ex- tends beyond and overhangs the cerebellum ; on the sides it overhangs and covers all. Looked at from above, nothins: is seen but this great ganglion. The ideal section (Fig. 50) rep- resents all these stages diagrammatically in Fig. 51. — Sab-fish stage, th, thalamus; o/, optic lobs ; m, medulla. one figure. After what has been said, the figure will be readily understood. PROOFS FROM EMBRYOLOGY. 147 Now, it is a most remarkable fact that substantially these same stages, which are permanent conditions in the Fig. 52. — Fish-stage, o/, olfactive lobe ; cr, cerebrum ; th, thalamus ; ol, optic lobe ; cb, cerebellum ; m, medulla. taxonomic series, are passed through as transient stages in the embryonic development of the human brain, and in the order given above. The very early condition of the human brain is represented in Fig. 51. It is evidently Fig. 53. — Reptile-stage. nothing more than the intercranial continuation of the spinal cord, enlarged a little into three swellings or gan- glia. These are the early representatives of the medul- la, the optic lobes, and the thalamus ; which last may be regarded as the basal and most fundamental part of the cerebrum. This stage may be regarded as lower than that of the ordinary fish. I have called it, therefore, the sub-fish stage. The cerebellum is a subsequent out- growth from the medulla, as is the cerebrum and olfac- 148 EVIDENCES OF THE TRUTH OF EVOLUTION. tive lobes from the thalamus. Fig. 52 may be said, there- fore, to represent "fairly the fish-stage. Henceforward the principal growth is in the cerebrum and cerebellum, both of which are subsequent outgrowths of the origi- nal simple ganglia, the medulla, and the thalamus. The cerebrum especially increases steadily in relative size, first becoming larger than but not coyering the optic lobes (Fig. 53). This represents the reptilian stage. Next, by Fig. 54. — Bird-stage, q/, olfactive lobe ; tibly, into one another, the ranges of species overlapping and in- PROOFS FROM GEOGRAPHICAL DISTRIBUTION". 169 B terpenetrating, and the two species coexisting on the borders of their ranges. This is represented by the diagram (Fig. 64), in which the horizontal lines repre- sent the north and south ranges of species of two groups, a and ^ B, separated by the dotted line. 3. Species also pass out gradually on the borders of — these ranges and others come in gradually, so far as number and vigor of individuals are concerned. If a a' and b b' (Fig. 65) represent the north and south range of two species, and b a' their overlap or area of coexistence, then the height of the curves A and b will represent the A B Fig. 64. Fig. 65. number and vigor of the individuals in different parts of the range. 4. While, therefore, there is a shading of contigu- ous groups into each other by overlap of species-ranges ; while there is also a gradual passing out of species so far as number and vigor of individuals is concerned, yet, in specific characters we observe usually no such gradation. Species seem to come in on one border with all their spe- cific characters perfect, remain substantially unchanged throughout their range, and pass out on the other border, still the same species. In other words, one species takes 170 EVIDENCES OF THE TRUTH OF EVOLUTION. the place of another, usually by substitution, not by transmutation. It is as if species had originated, no matter how, each in its own region, and had spread in all directions as far as physical conditions and struggle with other species w^ould allow. This important subject will be more fully discussed later. 5. We have thus far spoken of species as limited by temjierature alone, but they are limited also by harriers. If, then, there be an east and west barrier, such as a high mountain-range, or a wide sea or desert, there w^ill be no shading or gradation of any kind, because the barrier prevents overlapping, interpenetration, and struggle on the margins. For example : The species north and south of the Himalayas, or north and south of Sahara, are widely different. It is, again, as if they originated each where we find them and sjn^ead as far as they could, but the physical barrier prevented mingling and shading. 6. There are temperature-regions south as w^ll as north of the equator. Now, although the climatic con- ditions are quite similar, the sj^ecies of corresponding temperature-regions north and south are wholly differ- ent. It is, again, as if they originated wiiere we find them, and were kept separate by the barrier of tropical heat between. If carried over, they often do perfectly well. Continental Faunas and Floras. If the land-surfaces were continuous all around the globe, there is little doubt that each temperature region with its characteristic species would also be substantially PEOOFS FROM GEOGRAPHICAL DISTRIBUTION. 1^1 continuous. There would, it is true, be some local varia- tions dependent upon soil and humidity, etc., but sub- stantially the same species would exist all around. The distribution would be almost wholly zonal. But the in- teryening oceans are complete barriers to continental species. Hence we ought to expect, and do find, that the faunas and floras of different continents are almost to- tally different. Each apparently originated on its own continent, and did not spread to other continents, only because they could not get there. It is ne- cessary to explain this in more de- tail. Fig. 6(j repre- sents a polar yiew of the earth, showing the eastern and western conti- nents, and the five temperature zones already described. Now, if we examine the sj^ecies in each region, com- mencing at the pole, we find that those of Nos. 5 and 4 are almost identical all around. The reason is obvious. The continents come close together there, with ice-connection if not land-connection all around. Fig. 66. — Polar projection of the earth. 1, tropi- cal ; 2, temperate ; 3, sub-arctic ; 4, arctic ; 5, polar regions. 172 EVIDENCES OF THE TRUTH OF EVOLUTION. There is but one circumpolar region. But, as soon as we come down to No. 3 and No. 2, the species on the two continents are nearly all different, because there is an impassable barrier between, either in the form of ocean or of Arctic cold. For example, the animals and plants inhabiting the United States are almost whol- ly different from those in Europe, not only in species, but even largely in genera and to some extent in families. There are some exceptions to this rule, but these are of the kind which prove the rule, or rather the principle on which the rule is founded. These exceptions are mainly of three kinds : 1. Introduced si^ecies. — All our weeds, many garden-plants, and many animal pests are of this kind. They were not found here when America was discovered, only because they could not get here ; for, when brought here, they do so well that they often over- run the country and dispossess the native species, as we ourselves have done the Indians. 2. Hardy or else wide- migrating species. — Hardy species have wide range ; they may belong to No. 4 as well as No. 3. If so, they range down to No. 3 on both continents. Migrating birds, such as ducks and geese, etc., breed in summer in No. 4, and migrate southward in winter on both continents from the common circumpolar ground. 3. AJjnne sjwcies. — It is a curious fact that species on tops of snowy mountains in temperate regions of the two continents are wonderfully similar, though so completely isolated. We are not yet prepared to discuss this point. We shall do so later. Suffice it to say now that it can be completely explained. PROOFS FEOM GEOGRAPHICAL DISTRIBUTION. 173 In region No. 1 the continental diversity is still greater. Not only species and genera, but whole fami- lies and even orders, are peculiar to each continent. The great pachyderms — elephant, rhinoceros, hippopotamus — are peculiar to the Eastern ; the edentates — sloths and armadillos — to the Western. The humming-birds, those gems of the forests, of which there are over four hun- dred species, and the whole cactus family, are peculiar to America, while the tailless monkeys are equally char- acteristic of the Eastern Continent. The continents do not come together again toward the south, and, therefore, as might be expected, the great difference between the two persists to the southern points. The faunas of the southern points of South America, Africa, and Australia are very different. Subdivisions of Continental Faunas and Floras.— Be- sides the subdivisions of continental faunas, north and south, determined by temperature as already explained^ if there be in any continent an impassable barrier run- ning north and south, there will be a corresponding dif- ference in the species on the two sides, east and west. We give but one example : The North American Cordil- leras or Eocky Mountains, with their high ranges and desert plains, constitute a very great barrier between the eastern and western portions of the United States. Heuce, we find an extraordinary difference between the species inhabiting California and those found in the east- ern portion of the country. Speaking generally, all the species and many of the genera are peculiar. The ex- 171 EVIDENCES OF THE TRUTH OF EVOLUTION. ceptions, too, are significaDt. Leaving out introduced species, of which there are man 3^, they are mostly strong- winged or widely-migrating birds, such as the turtle- dove, the turkey -buzzard, the bald eagle, and, of course, many water-birds. Special Cases. — If any body of land is widely sep- arated from all other lands by deep seas, we invariably find a corresponding peculiarity of its species. Thus, the species inhabiting Australia and Madagascar are per- haps the most peculiar in the world. We do not dwell further on these, because we will discuss them hereafter. There is a little group of very small islands— the Gala- pagos — about six hundred miles off the western coast of South America, and surrounded on all sides by deep sea. These islands are stocked with a collection of curious animals not found elsewhere on the surface of the earth ; but among them are no mammals at all. We might multiply examples without limit. Even the rivers empty- ing in the same sea sometimes have each*its peculiar spe- cies of mussels. In the Altamaha River there are several species of unios — such, for instance, as the wonderful spinous unio — not found elsewhere. How came they there ? Howsoever they may have come there, they are now kept isolated there by barriers of land and of salt water. Many other curious details will come up in our dis- cussion of tlie origin of diversity. Marine Species. — Precisely the same princii^les apply here ; but diversity in the case of marine species is PROOFS FROM GEOGRAPHICAL DISTRIBUTION. 175 perhaps less marked, and certainly less general, because of the universal oceanic connection. Open-sea species are therefore almost universal. But many marine spe- cies are confined to shallow water, and therefore to shore-lines. The species on the two shores of the same ocean, or the two coasts of the same continent, are dif- ferent, being isolated east and west by barriers of deep sea or of land, and north and south by temjDerature. Also about isolated lands, like Australia and Madagas- car, the species are peculiar. Thus, then, species, genera, etc., are limited in every direction ; north and south by temperature, and in all di- rections by barriers, in the form of oceans, deserts, and mountain-chains. Add to these, peculiar climates and soils, and we see that, from this point of view, the whole surface of the earth may be divided and sub- divided into regions, sub-regions, provinces, etc. It would carry us too far to explain the primary and secondary divisions adopted by Mr. Wallace, and the somewhat different ones suggested by Mr. Allen. Our main object is to discuss the cause of this diversity, and especially to show the light shed upon it by the theory of evolution. We have only given a sketch of the facts sufficient for this purpose. Theory of tlie Origin of GeogrcqjMcal Diversity. It will be observed that all along we have assumed a sort of provisional theory. We have said in every case, it is as if organic forms originated where we find 9 176 EVIDENCES OF THE TRUTH OF EVOLUTION. them, and have gone thence wherever they could — as far in every direction as physical conditions and strug- gle with competing species would allow. This view has been formulated as the 'theory of specific centers of origin." There would be less objection to this as a first provisional theory did it not assume a supernatu- ral mode of origin. But, in the minds of those who hold it, it has usually assumed expressly or tacitly the form of ^'specific centers of creation,''^ thus implying the immutability of specific types and the supernatu- ralism of specific origin (page 68). In this latter or usual form it completely fails to account for the facts given above. For, if this were the mode of origin, each species ought in every case to be perfectly adapt- ed to its own environment, and to no other. But, on the contrary, introduced species often flourish better than in their own countrv, and better than the natives of their new homes. In the less objectionable form of *^ specific centers of origin," without defining the mode of origin, it accounts well for many of the more obvi- ous facts of geographical diversity, as it noio exists, but not all. According to this view, the amount of diver- sity ought to be in strict proportion to the complete- ness of isolation, or impassableness of the separating barriers ; but this is not exactly true. There is another element, not yet mentioned, which is just as important as impassableness, but which until recently has been left entirely out of account. This is the element of time — the amount of time since the barrier was set up, PROOFS FROM GEOGRAPHICAL DISTRIBUTION. 177 or during which ifc has continued to exist. These tAvo elements, it is true, are closely connected with each other ; for, since all changes in physical geography have taken place very slowly — since barriers in the form of mountain-ranges and seas have increased by slow pro- cess of growth — it is evident that impassableness is, to some extent, a measure of time. But they are by no means in strict proportion. The one or the other may predominate. Now, this time-element connects geographical distri- bution with changes of physical geography and climate in geological times, and especially with the latest of these changes, viz., those occurring during the Glacial ejjocli. During that remarkable epoch extraordinary changes of climate, from extreme Arctic rigor to great mildness, enforced wide migrations of species southward and northward ; while concomitant changes of physical geography, by elevation of the earth's crust over v/ide areas, opened highways between previously-isolated con- tinents, permitting migrations in various directions, and by subsequent depression again isolating the migrated species in their new homes. It is evident, then, that the recognition of the element of almost unlimited time at once introduces into the question of geographi- cal distribution the idea of evolution. If the study of geographical distribution, as it noiv exists, and as a part of science of physical geography, gave rise natu- rally to the theory of ^' specific centers of origin," the study of the same, in connection with geological time, 178 EVIDENCES OF THE TRUTH OF EVOLUTION. and as a part of geological science, now demands its explanation by the theory of evolution. It must be borne in mind, then, that geographical diversity of organisms is not a question of the present epoch only. There has been geographical diversity in every previous geological epoch ; it is, therefore, a ques- tion of geology as well as of biology. It is probable, however, that diversity has increased with the course of geological times, and is greater now than ever be- fore. In other words, in the evolution of the organic kingdom, the law of differentiation has prevailed here, as in other dejDartments of biology. A clear statement of the causes of the present distribution of organisms must embrace also the causes of geographical diversity generally. We give, therefore, at once a brief state- ment of what seems to us the most probable view, and shall then proceed to show how it explains the present distribution. Most Probable View of the General Process. — Bear- ing in mind, then, this time-element, the phenomena of geographical diversity are best explained by the fol- lowing suppositions : 1. A gradual progressive move- ment (evolution) of the organic kingdom, marching, as it were, abreast, at equal rate along the whole line — i. e., in all parts of the earth, and throughout all geo- logical times, under the action of all the forces or fac- tors, and following all the laws, of evolution already ex- plained (pages 19 and 73). If this were all, there would be no geograpliical diversity, although organic diversity PROOFS FKOM GEOGRAPHICAL DISTRIBUTION. 179 might be as great as it is now. There would be dif- ferentiatiou of forms and structure everywhere, but no differentiation of groups in different localities. 2. Under the influence of different conditions in different places, more or less isolated from one another by cli- matic or physical barriers, the onward movement (evo- lution) of organic forms takes different directions and different rates, and gives rise to local groups, which become more and more differentiated, without limit as time goes on. This element, acting by itself through- out all geological times, would ere this have produced an extreme geographical diversity, such as does not any- where exist. 3. From time to time, at long intervals, extensive changes of physical geography and climate, produced by crust elevations, partly enforce by change of temperature, and partly permit by opening of gate- ways, extensive migrations and dispersals of species, by which mingling and struggle for life and final readjust- ment takes place, and extreme diversity is prevented. Such mingling of different faunas and floras on the same ground, and the severe struggle for life that thus ensues, and the survival of the fittest in many directions, are, as already shown, among the most powerful factors of evo- lution. They tend to increase organic diversity, but to diminish geographical diversity. 4. At the close of such great periods of change as indicated in the last, by con- trary movement of the earth-crust — i. e., subsidence — new barriers are set up and new isolations are produced, and the process of divergence again commences and 180 EVIDEi^CES OF THE TRUTH OF EVOLUTION. increases steadily so long as the barriers continue to exist. Now. the last of these j^eriods of great changes and extensive migrations, and subsequent isolations, was the Glacial epoch. It was this epoch, therefore, which mainly determined the present geographical distribu- tion of species. Thus, the present distribution is a key to the directions of the last great migrations, and there- fore to the nature of the changes in physical geogra- phy and climate which then occurred ; and, conversely, the character of these changes, determined in other ways, furnishes the only hey to the present distrihution of species. Before applying the foregoing principles in the ex- planation of special cases, it may be well to give a very brief outline of the condition of things during the Gla- cial epoch. In America, during this epoch, by increasing cold the southern margin of the great northern ice-sheet crept slowly southward, until it reached the latitude of about 38° to 40°. Arctic sjoecies were thus driven southward slowly, from generation to generation, until they occupied the whole of the United States, as far as the shores of the Gulf, while temperate species were forced still farther south, into Central and South America. This period of extreme rigor and southward migration was followed by a period of great mildness, during which the ice and its accompanying Arctic con- ditions retreated northward, followed by Arctic species. PROOFS FROM GEOGRAPHICAL DISTRIBUTION. 181 More than one advance and retreat, apparently, oc- curred during this time. Again, during the same time, brought about by northern elevation, there was broader connection than now exists between North and South America, and free migrations between, in both direc- tions, enforced by extreme changes in temperature. Also, during this or previous time, there were broad connections between North America and Asia, in the region of Behring Strait, and between America and Europe, in high-latitude regions, and extensive migra- tions of faunas and floras between were thus permitted. The necessary result of all these migrations of species, partly enforced by changes of climate, partly 23ermitted by opening of gateways since closed, was exceptionally rapid changes in organic forms. This was the result of two causes : First, the severer pressure of a changing physical environment ; and, second, a severer struggle for life between the natives and the invaders. In Europe, during the same time and from similar causes, there were at least three or four different faunas struggling together for mastery on the same soil. First, there were the Pliocene indigenes, who had, if any, pre-emption right to the soil ; second, invaders from Arctic regions, driven southward by increasing cold ; third, invaders from Asia, permitted by the removal of the old sea-barrier which once extended from the Black Sea to the Arctic, and of whicli the Caspian and Aral are existing remnants, and thus opening a gateway for migration which has remained open ever since ; 182 EVIDENCES OF THE TRUTH OF EVOLUTION. fourth, invaders from Europe and Asia into Afiica, and sometimes back again into Euro2:)e, by opening of gateways through the Mediterranean, which have been since closed. One of these highways was through Gib- raltar, and one from Italy to Africa through Sicily. As in America, so here, in even greater degree, the severe pressure of changing environment and the severe struggle for life produced rapid changes of organic forms. Many species were destroyed ; others saved themselves by modifications adapted more perfectly to the changed conditions. There is little doubt that man came into Europe with the Asiatic invasion, and was one of the principal agents of change, especially in the way of destruction of many old forms. Such is a very brief outline of the last great geo- logical change and its general results. Being the last, this one has left the strongest and most universal im- press on the present geographical distribution. But similar changes by crust oscillations, if not also by extreme changes of climate, have repeatedly occurred in geological times, and some of the most remarkable geographical faunas and floras are the result of these earlier geological changes. AVe will now give a few examples illustrating these principles: 1. Australia is undoubtedly more peculiar in its fauna and flora than any other known country. Not only are all its species peculiar, not found elsewhere on the face of the earth, but its genera, its families, and even many of its orders of animals and plants, are PROOFS FROM GEOGRAPHICAL DISTRIBUTION. 183 also peculiar. These facts are so familiar that it is unnecessary to dwell on them. I need only mention, among plants, the whole of the simple-leaved acacias, already mentioned on page 86, of which there are so many species, and the whole family of the eucalyptids, of which there are several hundred species. Among animals I need mention only the order of monotremes, or egg-laying mammals, and nearly the whole order of marsupials, or pouched animals, of which there are over two hundred species. On the other hand, the true typical mammals are entirely absent, with the ex- ception of a few bats and a few rats, whicli have evi- dently been accidentally introduced from abroad. Another very noteworthy fact, which must be taken in connection with the last, is that Australian forms are far less advanced in the race of evolution than those of any other country — i. e., that many old forms which have long ago become extinct elsewhere are still retained there. A few examples will suffice. The mar- supials just mentioned are an old form once universally distributed, but now nearly extinct everywhere, except in Australia ; the cestracion, or Port Jackson shark, and the ceratodus, are Palaeozoic and Mesozoic forms retained only in Australia. What is the explanation of these remarkable facts ? We find the sufficient answer in the fact that Australia has been long isolated from all other countries. While geographical changes in geological times have mingled more or less the organic forms of other countries, and 184 EVIDEN"CES OF THE TRUTH OF EVOLUTION. the sharp struggle for life has j)roduced more rapid ad- vance and the production of many new and higher forms better armed for the battle of life, Australia has remained isolated from competition, and therefore comparatively un progressive. Can we tell when Australia was finally isolated ? Ap- proximately we can. The class of mammals is divided into two groups, which differ widely from each other ; so widely, that they are called sub-classes. These are placental mammals, or true typical mammals, and non- placental or rejitilian mammals. The non-placentals in- clude only the marsupials and the monotremes (ornitho- rhyncus and echidna). The monotremes actually lay eggs and incubate them. In the marsupials the embryo has no placental connection with the mother, and is born in a very imperfect condition, utterly unfit for in- dependent life, and placed in the pouch (marsupium), and permanenthj attached there to the teat until it is capable of independent life ; after which only it volunta- rily nurses like other new-borns. In other words, the gestation commenced in the womb is completed in the pouch. The uterine gestation in the opossum is only seventeen days, while the marsupial gestation is about two and a half months. In a kangaroo seven feet high in sitting position the embrvo at birth is only one inch long — a pink, hairless, almost amorphous mass. The monotremes are pure oviparous animals, like birds and reptiles. The marsupials might well be called semi- oviparous. In pure egg-layers the whole embryonic de- PROOFS FROM GEOGRAPHICAL DISTRIBUTION. 185 velopment is outside of the body ; in pure young-bearers the whole is within the body ; in marsupials it is paiUy within and partly without. Now — 1. The monotremes are found nowhere but in Australia and the neighbor- ing New Guinea. 2. The marsupials are also all con- fined to the Australian region, except a few oppossums in America. 3. There are some two hundred and thir- ty species of non-placentals in the Australian region. 4. As already said, there are no true mammals at all in Australia, except a few bats and rats which have come accidentally from abroad. 5. But non-placentals existed abundantly in Mesozoic times everyivhere, both in Eu- rop-Asia and in America, while true mammals did not appear at all on the surface of the earth until the Ter- tiary, when they almost immediately became very abun- dant everywhere, except in Australia. Evidently, there- fore, Australia was isolated before the Tertiary. The enormous diiference between its fauna and flora and those of other countries is due to at least three things : 1. So long an isolation necessarily produced great diver- gence of forms. This alone, however, would not affect the grade of organization. 2. Saved from wide migra- tions, and especially invasions from Eurasia, the great field of competitive struggle, it was left far behind in the race of evolution. Hence many of its forms are ar- chaic ; its mammalian fauna, for Instance, is still m the Mesozoic stage. 3. Its distance from other large conti- nents is so great that accidental colonization has been very slight, only extending to a few bats and a few rats. 186 EVIDENCES OF THE TRUTH OF EVOLUTION. I stop a moment to insist on the effect of competitive struggle in developing organic forms strong for the battle of life. Of all the continents, Eurasia has been the scene of most frequent geological changes, and therefore the arena of fiercest competitive struggle through wide and frequent migrations. Eurasian species, therefore, are the strongest of all. They have conquered wherever they have gone. Species in isolated regions are usually the weakest. The great moas and the dodo could not have continued to exist unless protected in a sort of bomb-proof. Kangaroos would now be quickly extermi- nated by the introduction of fierce Eurasian carnivores. 2. Africa. — The fauna of that part of Africa north of Sahara is essentially Mediterranean — i. e., a sub-group of the Eurasian. Sahara, rather than the Mediterranean Sea, is the true intercontinental barrier. The true Afri- can region, tlierefore, is south of Sahara. Now, accord- ing to Mr. Wallace, whom I mainly follow here, the true African mammalian fauna consists of two very different groups of animals. The one is a group of very small, curious animals, mostly low forms of insectivores and lemurs, very peculiar to this region, though more resem- bling those of Madagascar than of any other region ; the other is a group of large and powerful animals which dominate the region. These latter are similar to, though not identical with, those which inhabited Eurasia in Pli- ocene times. The great carnivores, pachyderms, and ru- minants of the region are examples of this group. Now, the explanation of these facts is as follows : The indige- PROOFS FROM GEOGRAPHICAL DISTRIBUTION. 18T nes of Africa are the animals of the first group. Africa, in Tertiary times, was isolated from the great field of combat, Eurasia, and therefore its animals were small, of low grade, and peculiar. During later Tertiary (Plio- cene) times, then, Africa was inhabited by animals of the first group, while Eurasia was dominated by animals of the second group. These two groups were then sepa- rated by the Desert of Sahara, or else by a sea in that re- gion. Some time during the Glacial epoch geographical changes removed this barrier, and climatic changes drove the Eurasian animals southward into Africa, where, find- ing congenial climate, they took possession of the conti- nent, dominating the feebler natives. Subsequently they were isolated there by the formation of the desert, and the process of divergence commenced, and has gone on to the formation of many new forms. Meanwhile the change, partly by extinction and partly by modification, has gone on still more rapidly in Eurasia, but in a dif- ferent direction. Hence, Africa is regarded as one of the primary faunal regions. 3. Madagascar. — This, next to the Australian, is probably the most peculiar faunal region known. There is probably not a single mammalian species found there which is known to occur anywhere else. It is remarkable also as the principal home of that strange, generalized, ancient form of monkeys — the lemurs. And yet its ani- mals, though very different, have a distant resemblance to those of Africa ; not, however, to the present dominant type, but to those we have called the indigenes. Not 188 EVIDENCES OF THE TRUTH OF EVOLUTION. ' one of the northern invaders is found there. The ob- vious conclusion from these facts is, that Madao-ascar was formerly united with Africa, and both were occupied by the same mammalian fauna (which may be called Af- rican indigenes, although they were considerably differ- ent from their descendants of the jDresent day), but be- came separated before the northern invasion. The effect of this invasion was to hasten the steps of change in the in- digenous fauna of Africa, partly by extermination, partly by modification, while the isolated portion in Madagascar went on at the usual slow rate of change in isolated re- gions. The time since the separation (which was cer- tainly during the Tertiary i^eriod) has been sufficiently long to produce very great divergence in both, but espe- daily in the African indigenes. In the fauna of Mada- gascar, therefore, we have a nearer approach to the origi- nal fauna of both. On account of this long isolation, we have here many ancient types which are extinct else- where. The lemurs are such an ancient type. These are a wonderfully-generalized type of monkeys — a connect- ing link between monkeys and other mammals, especially insectivores. As might be supposed, from the law of dif- ferentiation, already explained (page 11), they are the earliest form, the progenitors, of monkeys. In fact, in early Tertiary times, they were found not only in Africa and Madagascar, but all over the earth, as the only rep- resentatives of the monkey family. The true monkeys were not introduced until the mid-Tertiary. In Eura- sia and in America (which at that time was probably PROOFS FROM GEOGRAPHICAL DISTRIBUTION. 189 connected with Eurasia) wide migrations and frequent conflicts of faunas produced comparatively rapid evolu- tion of new and higher forms, while in isolated Africa old types continued until the invasion. Madagascar was spared this invasion, and therefore old types are still pre- served there. At present, at least three quarters of all lemurs are confined to Madagascar, although a few spe- cies are still found in Africa and in the great East Indian islands. 4. Island-Life. — Mr. Wallace has divided islands into two kinds, continental and oceanic islands. The division is undoubtedly a good one, although we may not always be able to refer an example with certainty to the one or the other class. Continental islands are those on the bor- ders of continents, and separated from the latter only by slialloiu ivater. Oceanic islands are those, usually very small, found in the midst of the ocean, with abyssal depth all about. Continental islands may be regarded as appendages to the neighboring continent — as outliers of continents separated by submergence, and have, in fact, been thus formed. Oceanic islands have been formed geologically recently by volcanic action building up from the sea-bottom. Continental islands have a continental structure — i. e., they are composed of stratified as well as of igneous rocks. Their structure is a record of geological history, like that of the neighboring continent. Oceanic islands are composed wholly of volcanic rocks ; or, if there be any stratified rocks, these are only of the most recent date. As examples of continental islands we 190 EVIDENCES OF THE TRUTH OF EVOLUTION". have New Zealand as an appendage of Australia, the great East Indian (Borneo, Java, Sumatra, etc.) and the Japanese Islands, etc., as appendages of Asia ; the British Islands, appendages of Europe ; the West Indian Islands, appendages of America ; Madagascar, an appendage of Africa, etc., etc. As examples of oceanic islands we have the Azores and Bermudas in the Atlantic, and the Polynesian islands in mid-Pacific. a. Continental Islands. — Now, the fauna of conti- nental islands, as might be expected from the mode of origin of these islands, is similar to, though not identical with, that of the neighboring continent ; the amount of difference being in proportion to the length of time since they were separated and the width of the separatio7i. Madagascar, for example, has been long separated from its parent continent, and by a wide and deep channel. Its fauna, therefore, differs greatly from that of Africa, although resembling it more than that of any other country. The separation of JVciv Zealand from Aus- tralia has been not quite so long, and the divergence, therefore, is not so great. These two will be sufficient illustrative examples of long separation, and therefore of great differentiation of forms. On the other hand, the British Isles are an excellent example of comparatively recent separation. These isles have probably been several times united and separated from Europe, but we are here concerned only with the more recent. They are now separated from the conti- nent and from one another only by shallow seas. An PROOFS FROM GEOGRAPHICAL DISTRIBUTION". 191 elevation of less than six hundred feet — geologically a yerv small chaiis^e — would bare the bottoms of the Irish and English Channels and the North Sea, and connect Fig. 67. — Map of outline of coast of Western Europe, if elevated 600 feet (after Ljcll). 192 EVIDENCES OF THE TRUTH OF EVOLUTION". these islands with one another and with the continent (Fig. 67). Now, it is well known that there were dur- ing the Glacial epoch, and subsequently, several oscilla- tions of level sufficient to connect and separate these islands. In the mid-Glacial ei:»och the British Islands, by submergence, were nearly obliterated, being reduced to an archipelago of small islets representing the high mountains of Wales and Scotland. The Pliocene fauna and flora were, therefore, largely exterminated. During the close of that epoch they were elevated above the present condition and broadly connected with the con- tinent (Fig. 67), and the newly-exposed land was taken possession of by European species, man among the num- ber. Still later — i. e., at the beginning of the present epoch — the islands by subsidence were again separated, but not widely, from the continent. This is the condi- tion now. What, then, was the result ? 1. The fauna and flora of the British Isles are substantiallv the same, but less rich in species than that of Continental Europe, some of the European species being wanting. This shows that the last connection was not a long one ; the coloni- zation had not been completed before re-isolation. 2. This poverty of species is more conspicuous in Ireland, because colonization is progressive in space as well as in time. Some species had not reached so far when Ireland was re-isolated from England. The conspicuous absence of snakes, for example, is thus accounted for. There is, we all know, another theory to account for this, but we prefer the natural one. 3. The difference between Brit- PROOFS FROM GEOGRAPHICAL DISTRIBUTION. 193 isli and European fauna and flora is very small, it is true, but there is some difference, val'ietal if not specific. The reason is, that the time since separation is too small to produce much divergence, and the width of the exist- ing barriers not great enough to prevent colonization by accidental causes. The continental islands of the southern coast of Asia are good examples of an intermediate condition as to the length of time since separation, and of the consequent degree of differentiation of the faunas and floras. Coast-Islands of California. — We give one more exam- ple, and dwell upon it a little, because it occurs on our own coast. The recent studies of Mr. E. L. Greene on the flora of the islands off the coast of California have brought to lioht some facts which are an admirable illustration of the principles laid down above. On looking at a good map of California, any one will observe eight or ten islands, some of them of consider- able size, strung along the coast from Point Conception southward, and separated from the mainland by a sound twenty to thirty miles wide. They are in structure true continental islands — outliers of the mainland separated by a subsidence of a few hundred feet. Moreover, the date of their separation is known. They were certainly connected with the mainland during the later Pliocene and early Quaternary, for bones of the mammoth, char- acteristic of that time, have been found on one of 194 EYIDEXCES OF THE TRUTH OF EVOLUTION. them.* They were therefore separated during the Gla- cial epoch. The main i^eculiarities of the flora of these islands are the following : 1. Out of nearly three hundred species of j^lants gath- ered by Mr. Greene, about fifty are wholly peculiar to these islands. 2. Of the remaining two hundred and fifty species, nearly all are distinctively Calif ornian. In other words, the distinctively Californian forms are very abun- dant, while the common American forms are rare — i. e., the island flora is distinctively Californian, with many peculiar species added. I explain these facts as follows : The whole coast- region of California is geologically very recent, having emerged from the sea as late as the beginning of the Pli- ocene epoch. As soon as emerged it was of course colo- nized from adjacent parts. Since that time its peculiar flora has been formed by gradual modification. The en- vironment has been sufficiently joeculiar, the isolation sufficiently complete, and the time sufficiently long, to make a very distinct group of organisms. It is one of Mr. Wallace's primary divisions of the Ne-arctic region. During late Pliocene and early Quaternary times, as already said, the islands were still a part of the mainland, and the whole was occupied by the same species, viz., the distinctively Californian species now found in both, together, as I suppose, with the peculiar island species. * "Proceedings of the California Academy of Science," vol. v, p. 152, 1873. PROOFS FROM GEOGRAPHICAL DISTRIBUTION. 195 During the oscillations of the glacial times the islands were separated by subsidence of the continental margin. Simultaneously with this subsidence, or subsequently thereto, came the invasion of northern species, driven southward by glacial cold. Then came the mingling of invaders with natives, the struggle for mastery, the ex- termination of many forms — viz., the peculiar island spe- cies — and the slight modification of others, and the final result is the California flora of to-day. But the island flora was spared this invasion by isolation. Therefore the invading species are mostly wanting, the distinctive island species were saved, and the result is the island flora of to-day. The island flora, therefore, somewhat nearly represents the Pliocene indigenes of both. It will be observed that this case is somewhat like that of Madagascar, but with a characteristic difference. In the case of Madagascar, the separation has been long. The extreme peculiarity of its fauna is the result partly of progressive divergence and partly of many forms saved by isolation. In the case of the coast-islands of Califor- nia, the time has not been long enough for any great divergence by modification. The peculiarity of its spe- cies is due almost wholly to species saved by isolation.* b. Oceanic Islands. — We have seen that faunas and floras of continental islands are somewhat similar to those of the neighboring continent, though with varying degrees * For fuller discussion of this subject, see " Bulletin of the Califor- nia Academy of Science," No. 8, 1887, and "American Journal of Sci- ence," for Dec, 1887. 196 EVIDENCES OF THE TRUTH OF EVOLUTION. of difference— the amount of difference, or divergence by evolution, being in proportion to the amount of time and the impassableness of the separating barriers. But ocean- ic islands have never been connected with any continent. They are new land formed in the midst of the ocean by volcanic action. When they first appeared they were, of course, without inhabitants of any kind, animal or vege- tal. How were they peopled ? We answer by ivaifs from here and there — by castaivays from other lands. The dominance of particular kinds will depend on the direction of winds and currents, bringing from some lands more than others, and upon the kinds of animals or seeds of plants most liable to be successfully carried across wide seas. Their faunas and floras, therefore, are characterized by a mixture of species resembling, though not usually identical with, those of various lands, with a predominance of those of some one land, and by the singular and complete absence of mammals and amphib- ians, these being unlikely to be transj)orted by floating timber, as are small reptiles and insects, etc. Among mammals, however, there is a significant exception in favor of bats, the reason being both their power of flight and their habit of concealment in hollow trees, etc. To this explanation, however, we must add that divergence by isolation will meanwhile go on in proportion to time. The Azores, for example, have been peopled from Eu- rope, Africa, and America, but mostly from Europe, on account of the prevailing winds and currents being favor- able to colonization from that direction. There are PROOFS FROM GEOGRAPHICAL DISTRIBUTION. 197 many curious peculiarities in the species, howeyer, be- cause colonization is very slow, and divergent variation has been going on pari passu. The Bermudas, on the other hand, have been colonized mainly from America, because of the current of the Gulf Stream. These few examples are sufficient for our purpose, which is only to illustrate the causes of geographical dis- tribution. If any one desires to pursue this interesting subject, we would refer him to that most fascinating book, Mr. Wallace's ^Island-Life." 5. Alpine Species. — These afford an admirable illus- tration of the fact that in isolated faunas and floras the amount of difference is proportioned not only to the comj^leteness of isolation, but also and mainly to the time of isolation. It is well known that Alpine species — i. e., those spe- cies inhabiting the region bordering the joerpetual snow of lofty mountains — are very siuiilar to one another, even in the most distant localities, where their isolation from one another is as complete as possible ; as, for example, in the high Alps of Europe, the high mountains of Colo- rado and California. Why is this ? We find the key to this mystery in the additional fact that they are similar also to Arctic species. A somewhat full explanation is here necessary. During Miocene times, magnolias and taxodiums (bald cypress), like those in forests and swamps of Carolina and Louisiana, and sequoias and libocedrus like those now in California, and many other temperate - region 198 EVIDENCES OF THE TRUTH OF EVOLUTION. forms of plants, grew abundantly in Greenland, and north- ward certainly to 75° north latitude. At that time there could not have been any perpetual polar ice, and there- fore no Arctic species, unless on high mountains in polar regions. In Pliocene times perpetual polar ice, and there- fore Arctic species, probably commenced to appear. As the cold of the Glacial epoch came on and increased in severity, the j)olar ice extended southward as a general ice-sheet, until it reached in America 40° and in Europe about 50° north latitude. In the United States its mar- gin can be traced as a distinct moraine through Long Island, middle ^ew Jersey, middle Penns3^1vania ; thence, less distinctly, following the Ohio River, crossing the Mis- sissippi ; thence following the Missouri, on its south side, into Montana. By the increasing cold, Arctic species were driven slowly southward, generation after genera- tion, until they occupied the whole of the United States to the Gulf, and the whole of Europe to the Mediterra- nean. As these species on the two continents came from a common home in polar regions, they were similar to one another, except in so far as some slight divergent modification may have been 2:)roduced during their south- ward travel. When the glacial rigor declined, and the ice-sheet gradually retreated to its present position, Arc- tic species, following the snow-edge, went also north- ward, on both continents, to their present home in jiolar regions. But there was an alternative vray of migration left open which was embraced by certain plants and in- sects. While on both continents most individuals went PROOFS FROM GEOGRAPHICAL DISTRIBUTION. 199 northward^ some of them went upward, following the snow- edge into high mountains, and were left stranded there. Thus it has come to pass that the plants and insects of high mountains in temperate regions of different continents, though so widely separated and impassably isolated, are extremely similar to one another. But, though similar, they are rarely identical. The time has been long enough for some but not very great divergent modification. It is impossible to conceive a more beautiful illustration of the principles we have been trying to enforce. Thus, then, undoubtedly all the ^^henomena of geo- graphical distribution of sj^ecies are most rationally explained on the principle of slow evolution - changes, different in different places, and increasing with the time of isolation and its completeness. Objection. — The only objection which can be raised against this view is the manner in which contiguous geo- graphical faunas and floras pass into one another when they are limited not hy harriers hut hy temperature. In passing from equator to poles, over continuous land, we of course pass through many successive faunas and floras, limited wholly or mainly by temperature. Now, if species are indeed indefinitely modifiable, then on the bor- ders of contiguous faunas or floras, where one species dis- appears and another closely allied but adapted to a colder temperature takes its place, the one species (say the anti- evolutionists) ought to be gradually transmuted into the other, so that all the gradations may be traced. But this 10 200 EVIDENCES OF THE TRUTH OF EVOLUTION. is certainly not usually the fact. On the contrary, a species may indeed pass out gradually, and another come in gradually, so far as numher and vigor of individuals are coyicerned ; but, in specific character, they may be said, usually at least, to come in suddenly, with all their characters perfect, remain unchanged throughout their whole range, and pass out suddenly at its borders. Another species takes its place, overlapjoing in range and coexisting on the borders of both ; this also continues unchanged, as far as it goes, and so on. The change from one fauna to another is apparently not by transmu- tation of one species into another by gradations, but by suhstitution of one perfect species for another perfect species. As a broad general statement, the condition of things is precisely such as would be the case if specific types were substantially immutable by physical con- ditions, but were originated in some inscrutable way (created) in the regions where we now find them, and have spread in every direction as far as physical condi- tions and struggle with other species w^ould allow them — their ranges therefore interi^enetrating and overlapping one another on their borders. Two characteristic examples will make our meaning clear. There is not a more characteristic tree known than the sweet-gum, or liquidambar. This tree grows from the borders of Florida to the shores of the Great Lakes. It may indeed be most numerous and vigorous somewhere in the middle region, and may die out grad- ually in number and vigor of individuals on the borders PROOFS FROM GEOGRAPHICAL DISTRIBUTION. 201 of its range, but in specific character it is substantially the same throughout, easily recognizable by its dense wood, its winged bark, its five-starred leaf, its spinous burr, and its fragrant gum. Physical conditions may diminish its number and vigor, and limit its extension, but seem powerless to essentially modify its specific char- acter. It seems to give up its life rather than change its nature. Another striking example : The sequoias (redwood and big-tree) are entirely confined to California, and there are only two species now existing, viz., the redwood (S. sempervirens) of the Coast Ranges, and the big-tree {S. gigantea) of the Sierra Nevada. Doubtless they are most numerous and vigorous somewhere in the middle of their range, and die out gradually in number and vigor on the borders north and south, being replaced there by other genera better adapted to the physical conditions ; but in specific character they remain essen- tially unchanged throughout. They are everywhere the same — easily recognizable by wood, bark, leaf, and burr. Both in this case, and in the previous one of the sweet-gum, it is as if they were created perfect in their present localities, and have spread in all directions as far as physical conditions and the struggle with other competing species would allow ; but physical conditions seem powerless to change them into any other species by ada^Dtive modification. Answer. — We have, we believe, stated the objection fairly. The answer is, that the elements of time and 202 EVIDENCES OF THE TRUTH OF EVOLUTION of migrations have not been taken into the account. In fact, this objection was conceived and formulated before the idea of geological time was fully assimilated by the human mind, and our theories of origin adjusted to it. If these species did indeed originate where we now find them, and in the present geological epoch, the argument might at least be entertained ; but this is not the fact. We know something of the geological history of all these species, and the history of the migrations of some of them. We know that sweet-gums were abundant and of many species in the United States in Tertiary times, and all have become extinct excejit this remnant. Whatever of modifications there were must be looked for at or about the time of its origin in Tertiary times, not now. Species, like individuals, are j^l^stic only when young. This one has already become rigid, and all the more so as it is a remnant widely separated from other species. For competition is strongest and most effective with nearest allies. Present species are mostly isolated remnants — terminal twiglets of the tree of life. Twiglets are of course widely separated at their visible ends. Their points of union with other twiglets must be sought below. In the case of the sequoias, we know something also of the history of their migrations. In Miocene times they were abundant, and of many species in circumpolar regions. Some twent3^-four species of fossil sequoias are known, fourteen of which are Tertiar}-. By the cold of the Glacial epoch they were driven slowly south- PROOFS FROM GEOGRAPHICAL DISTRIBUTION". 203 ward, botli in America and in Europe — in America as far as Southern California. After the Glacial epoch, and the return of temperate conditions, they doubtless at- tempted to go northward again ; but these great changes were too much for them ; they were wholly exterminated in Europe, and nearly so in America. A few were left stranded high up on the slopes of the Sierra Nevada, and on the cool, moist sloj^es of the Coast Eanges. The species now in California are not identical with those found in the Miocene strata of Greenland ; but the difference is only what we might expect after such ex- tensive migrations and such long and severe struggle for life. Further, it is noteworthy that the Miocene species fall into two groups, viz., the yew-like leaved and the cypress-like leaved. These are represented to- day in California, the one by the redwood, the other by the big-tree. They are evidently direct descendants of the Miocene species, though somewhat modified. But it will be objected that there ought to be some cases of transitional forms showing transmutation — in fact, there ought to be some cases of species now form- ing under our eyes. There are, we believe, examj^les of such cases. But intermediate forms are not likely to be maintained long, especially if migrations occur to give rise to severe conflict of forms. In that case the intermediate forms are soon eliminated, and species become distinct. This important point will be dis- cussed more fully in the next chapter. CHAPTER VIIT. PROOFS FEOM ARTIFICIAL PR0DUCTI0:N" OF VxVRIETIES, RACES, SPECIES, ETC. As already stated, page 40, the use of the method of experiment in the field of biology is, unfortunately, Yery limited. Neyertheless, it is already beginning to be used more and more in the department of physi- ology, and may be used also, to a limited extent, in the department of morphology. It is true that direct scientific experiments, for the express purpose of pro- ducing permanent modifications of form, and thus test- ing the theory of evolution, are of comparatively little value as yet, because the all-important element of time is wanting. The steps of evolution are so slow, and the time necessary to produce any sensible effect is usu- ally so great, that, in comparison, man's individual lifetime is almost a vanishing quantity. But, from time immemorial, experiments have been unconsciously made by man on domestic animals and food-plants, which bear directly on this subject. All domestic ani- mals and food-plants, and many ornamental flowering plants, have been subjected for ages to a process of PPvOOFo FROM ARTIFICIAL PRODUCTION. 205 artificial selection acting upon natural yariation of off- spring. As wild species are modified, we believe, in- definitely by divergent variation and natural selection, so domestic species are modifiable certainly largely, perhaps indefinitely, by divergent variation and artifi- cial selection by man. We all know the extraordinary modifications which have thus been gradually brought about in domestic animals, such as dogs, horses, sheep, pigeons, etc.; in food-plants, as cereal grains, garden- vegetables, etc., and in ornamental jolants, as roses, dahlias, pinks, etc. We can only give very briefly the principles of the process by which these extreme modi- fications are i3roduced, referring the reader to works specially devoted to this subject for more complete ac- counts. Let it be borne in mind, then («), that inheritance is not only from the immediate parents, but from the whole line of ancestry. The inheritance from the im- mediate parents is, doubtless, usually greater than from any other one term of the ancestral series — the effect on the offspring of any previous generation becomes, doubtless, less and less as the distance from the off- spring increases — yet the sum of the ancestral inherit- ance is far greater than the immediate jiarental. Let it also be borne in mind {h) that true breeding from one form for many generations creates a fund of he- redity in that form, and thus tends to produce fixity, rigidity, or permanence in that form. Now, the method of producing artificial breeds, some- 206 EVIDENCES OF THE TRUTH OF EYOLUTIOX. times consciously, sometimes unconsciously, is, briefly, as follows : Suppose it be desired to obtain a yariety of an animal, say a dog, having a certain character. We start from a common type, a (Fig. 68). If this type Tig. CS. were allowed to breed naturally, the slight divergent variation of offspring represented by the radiating lines would neutralize one another by interbreeding, the indi- vidual differences would be ^^ poolecV in a common stock, and the S2:>ecies would remain substantially con- stant. But if among all these slightly divergent vari- eties we select one, 1), which seems in the right direc- tion, and ruthlessly destroy all the others (indicated by crossing them out by the circular line), and breed this variety, l, only, we shall get again a number of di- vergent varieties. It may be that the larger number of these will be backward, in the direction of the orig- inal type «, on account of the ancestral heredity in that direction, but some will again be in the desired direction. Let all the varieties other than the desired one, but especially the backward-going or reverting ones, be again destroyed, and the one kind only selected which seems to be in the right direction, viz., c. As PROOFS FROM ARTIFICIAL PRODUCTION. 207 we push the form thus from generation to generation in the desired direction, especially if we attempt to hasten too much the process, the resistance to moye- ment — if I may use the expression — in that direction becomes greater and greater (shown by the decreasing distances between the successive points of divergence, a, h, c, d, etc.), and the tendency to reversion becomes stronger (shown by the greater number and length of the backward-going lines), until finally it is almost impossible to push any farther. We will su2')pose that X is such a limit. But if, now, we breed true on the point X, destroying tlie reversions or backward varia- tions for many generations, we will gradually accumu- late a fund of ancestral heredity on this point which increases with every added generation, until finally the tendency to reversion becomes small. The variety 'breeds true without further interference, or with only very general superintendence. Such a permanent va- riety is called a race. After a race is firmly established for a sufficient length of time, and the tendency to reversion is lost, it may itself become a new point of departure for the formation of new varieties or races, in the same or other directions. Thus, during even the brief history of man, have been formed races of the different domestic animals, and useful and ornamental plants, differing so greatly from each other that, if found in the wild state, they would unhesitatingly be called different species, or even in some cases different genera. Now, if art can vary form so greatly, and in so 208 EVIDENCES OF THE TEUTH OF EVOLUTION. short time, why may not Nature in limitless time ? If art by artificial selection, why not Nature by natural selection ? Nature is as rigid in selection and as ruth- less in destruction : why may we not expect similar or even much greater results ? The process is similar in the two cases — i. e., selection among varieties in oil- spring, only that the selection is natural instead of artificial, and the process is so slow that there is little tendency to reversion in the latter case. Suppose, then, we have a gradually changing physical environ- ment, or climate. Among the divergent varieties of any species in each generation, those would be pre- served which are most in accordance with the new climate, and the others would perish. This is natural selection, or survival of the fittest. Add to this the effect of the change in the organic environment. All species are modified by the changing physical environ- ment* but these modified species again all affect one another in the com2:)etitive struggle for life, and the strongest or swiftest, or most cunning, survive (natu- ral selection). Add to this, again, the struggle among the males for possession of the females — for reproductive opportunities — by which only the strongest and most courageous, or the most beautiful and attractive, leave progeny which inherit their peculiarities (sexual selec- tion). Add to these, finally, ynigrations, voluntary among higher and involuntary dispersals among lower animals and plants, and the consequent mingling of faunas and floras — the migrations subjecting them to PROOFS FROM ARTIFICIAL PRODUCTION. 209 great change of enyironment, both physical and or- ganic, and the mingling ^^roducing fiercer struggle for life — and we have in powerful operation many causes of modification. Add, I say, all these causes of modi- fication together, and then make the process slow and continuous through unlimited time, and where is the limit to the degree of change ? Commencing in any species, from any point of departure, there are formed first slight modifications which would be called yari- eties ; then these modifications, continuing in the same direction, form races ; these races by wider separation become species, and species in their turn become gen- era, etc. Comparing, again, to a growing tree, yari- eties are swelling buds ; when they grow into twigs, they are species ; when they branch again into different species, the branching stem becomes a genus, etc. We haye thus far spoken only of the yarious forms of one factor, yiz., the Darwinian factor of selection, whether natural or artificial. We haye dwelt upon this oncj because the natural and the artificial processes are so similar, and the artificial is so controllable. But there are other factors in operation, in art as well as in na- ture. We haye already spoken (p. 73) of other factors of natural change. We haye shown how changing physical enyironment affects function, and function affects form and structure^ and how these slight changes are integrated by heredity through many gen- erations. We haye also showai how use or disuse in- creases or diminishes the size and change the form of 210 E\^IDENOES OF THE TRUTH OF EVOLUTION parts, and these changes, also,, however slight, are in- tegrated by heredity. Now, these factors are operative also in domestication of animals and cultivation of plants. No environment is so new and peculiar as domestication and cultivation. The soil and temperature in plants, food and housing of domesticated animals, tend to change form and structure of the offspring, although in a way which it is difficult intelligently to control, and thus are prolific of varieties from which to select. In fact, they often give rise to great and unexpected modifications, called sports, which form jDoints of dejDarture for new varieties and races. Now, in nature, not only are all these causes and factors of change in constant operation, hut they act together in a peculiarly com2:)lex way. All the members of a fauna and flora, and the physical environment of any locality, constitute together a most complex and delicately ad- justed system of correlated parts. A change in one part is propagated through the whole system ; also, a change in one factor affects all other factors. When we add to this the large amount of time, in comparison with indi- vidual human life and observation, necessary to produce visible change of form, we can easily understand why the process is still imperfectly understood, although tlie fact is certain. But it will be asked, Are there, then, no differences between the artificially made extreme varieties equiva- lent, so far as difference of form is concerned, to species, and real natural species ? There are. If there were not, PROOFS FROM ARTIFICIAL PRODUCTION. 211 tliere would neyer have been any doubt about the deriva- tive origin of natural species. But if it be asked, Are not these differences fundamental, and therefore fatal to the argument for evolution derived from this source ? we answer, we think not. We will deal frankly and fairly with these differences. First Difference, Reversion. — The strong tendency of artificial varieties to reversion, even during the process of formation, and especially their complete reversion to the original type if the hand of man be withdrawn — i. e., if left to themselves, or become wild — is supposed to show an essential difference between such varieties, however extreme, and true species — is supposed, in fact, to prove an indestructible permanency of specific types. Nature disowns these artificial forms, and as it were brands them with bastardy. Not only so, she strives ever to destroy them. The supporting hand of man is necessary to sustain them. Left to themselves and to Nature, they quickly revert to the original type. If all the extreme varieties of dogs, from the greyhound and New^foundland, on the one hand, to the terrier and lap-dog on the other, were turned loose on an isolated island, uninhabited by man but full of other animals, and left there to shift for themselves — and the island were visited again after a lapse of a hundred or a thousand years — it is probable that a uniform species, something like to, though per- haps not identical with, the wolf, would be found. They would have reverted to the original or nearly the origi- nal wild type from which they were produced by domes- 212 EVIDENCES OF THE TRUTH OF EVOLUTION. tication. All or nearl}^ all that was done by man would have been undone by Nature. This reversion is one test of species. But the reason of this tendency to reversion is ob- vious : First, the time was too short, the rate of change was too rapid, in the artificial formation of these varieties. There was not time enough to accumulate a fund of he- redity on each successive stage of the change. Therefore the form is unstable and the tendency to revert is strong. Compare the fleeting days and the hurrying impatience of man with the infinite time and the divine patience of Nature ! But mere instability is not the principal cause of reversion. Secondly, in the case of artificial forms in a wild state, natural selection compels 7rversion. Every species in a wild state must of course be in harmony with the environment. But artificially made forms are in harmony with the artificial environment of domestica- tion, but not with the environment of nature. In nature the fittest survive, but artificial breeds are not fit to sur- vive in a state of nature. They are therefore quickly destroyed in the struggle for life, or must be modified. Nature immediately begins to select the fittest, and gradually in the course of time ]3roduces one or more uniform species, similar to that from which they came, or perhaps to what they would have been by this time if left to the operation of natural causes under the condi- tions supposed. But natural species, if they are formed, as the derivationists suppose, by the operation of natural causes, can not revert unless the conditions revert ; for PROOFS FROM ARTIFICIAL PRODUCTION. 213 the same causes which operated to produce, still con- tinue to operate to keep, the species. Take an example : The form, the habits, and the instincts of the pointer have been made by a slow process of artificial selec- tion of diyergent varieties of o:ffspring, and by training of individuals continued and its effects accumulated throusfh many generations. But this form and these habits and instincts, so laboriously produced, would be quickly de- stroyed by Nature. The pointer, left to himself, must either change or become extinct, because not adapted to the wild state. Such instincts and habits would not only be of no use, but would be incompatible w^ith success in the struggle for life. But suppose for a mo- ment that these habits and instincts were useful to the animal in a wild state ; evidently they would be in- stantly seized upon by natural selection, and not only perpetuated but intensified until a very distinct species would be produced. The same is true of all other races of dogs. If the Newfoundland, the greyhound, and the pug were all turned loose in a forest, and if each of these kinds were admirably adapted to some place in the econ- omy of Nature — for some special mode of food-getting without corresponding disabilities in other directions (as must be the case if made by natural selection) — there can be no doubt they would each survive, and their charac- ters intensified ; intermediate forms would disapjDear (for reasons which we shall see presently), and we would soon have three distinct species, or perhaps we would even call them distinct genera. 214 EYIDEXCES OF THE TRUTH OF EVOLUTION. Second Diiferenee, Intermediate Forms,— Xatural spe- cies are distinct — marked out with hard and fast lines — while artificiallj-made races, even though in their t}^ical forms thej differ as much or more than natural sj^ecies, shade into one another bj insensible gradations. In an- swer and exjolanation of this difference we remark : If species or modified forms of any kind, whether natural or artificial, are made bv natural causes, and not at once out of hand by supernatural creation, then of course there must have been gradations in the process of mak- ing. Now, in the artificial case, the whole j)rocess as well as the result lies within the limits of observation, while in the natural case onlv the final result. But it will be asked, Why are the gradations not seen also in the final result ? We answer, because the intermediate forms are eliminated in the struggle for life, and not re- produced by cross-breeding. If artificial races always bred true — i. e., without crossing, as natural species do — they would j^robably soon.be as sharj^ly demarked. Cross- breeding is the great cause of the shadings between do- mestic races. This brings me to the third and most im- portant difference. Third Difference, Cross-Fertility. — Artificially-made races breed freely and without repugnance with one an- other, and the offspring of such cross-breeding is in- definitely fertile. Natural species will not usually unite with one another, being prevented by sexual repugnance and other causes. Or, if they do sexually unite, there is either no offspring, or else the offspring is sterile, PROOFS FROM ARTIFICIAL PRODUCTION. 215 and therefore the intermediate form dies out in the first generation ; or else the offspring is imperfectly fertile, and therefore the intermediate form is elimi- nated in a few generations, and the species remain distinct ; or else the offspring is more fertile with the parent stocks, and therefore revert to the parent stocks^ and still the species remain distinct. Such infertile, or imperfectly fertile, offspring — the result of crossing of species — are called hybrids. This is regarded as a most important test of true species, as contrasted with varieties or races. There are two bases on which species may be founded. Spe- cies may be based on form, morphological species ; or they may be based on reproductive functions, physio- logical species. By the one method a certain amount of difference of form, structure, and habit, constitutes species ; according to the other, if the two kinds breed freely with each other and the offspring is indefinitely fertile, the kinds are called varieties, but if they do not they are called species. The two tests, however, do not always accord. Every now and then we find undoubted morphological species which may be crossed and produce indefinitely fertile offspring. Yet it is certainly true that species are usually cross-sterile, while varieties, whether natural or artificial, are cross-fertile. In explanation of this important difference, let it be observed that there are here two things which must be kept distinct in the mind, although they are, doubt- less, closely allied — viz., sexual repugnance (psychologi- 216 EVIDENCES OF THE TRUTH OF EVOLUTION. cal element) and cross-sterility (physiological element). The former is fonnd, of course, only in the higher animals, where fertilization is voluntary. The latter is universal among all living things. This latter, there- fore, is the more fundamental and essential element, and the former may be regarded as' its psychical sign in the higher animals. It is of this latter, therefore — i. e., cross-sterility — that we shall speak mainly. Suppose, then, w^e have growing together in the same locality many species of pines or oaks, or other ane- mophilous trees. The whole air is filled with the pollen of many species, and every germ-cell must receive many kinds of male cells, and yet there are no hybrids, but, on the contrary, the species remain distinct. So also in case of hermaphrodite animals, where the fertilization is involuntary ; many aquatic species are found together in the same locality, and the water is filled with sperm- cells of many different species. Many kinds of sperm- cells must fall on each germ-cell, and yet there are no hybrids ; the species remain distinct. In all such cases we must suppose that there is, among the different kinds of male cells, a struggle for the possession of the germ or female cell, or a sort of sexual selection by the female cell among the competing male cells, and the fittest — the most in accord; i. e., those of the same species — prevail. This is universal. But in the higher ani- mals, in addition to the prepotency of male cells of the same species, and comparative infertility in case of union of those of different species, sexual attraction and sexual PROOFS FROM ARTIFICIAL PRODUCTION. 217 repugnance contribute to the same result, and species are thus doubly separated. Thus sexual selection is of two kinds : selection of individuals for union (psychical), and selection of sperm-cells for fertilization (physiologi- cal). The one kind is usually the sign of the other — attraction the sign of fertility, and repugnance of sterility. But in the domestic state it is all otherwise. Free competition between individuals or between cells is not allowed. Thus, for example, among plants, crossings may be forced and hybrids made in gardens which would never occur in Nature. The florist prevents fertilization in the same kind and compels fertilization of a different kind. If male cells of the same kind were allowed to compete, the result would be different. Doubtless the same method would succeed in many lower animals. So also in higher animals free competition and sexual selection for union are often not allowed, and therefore animals of different species, such as the horse and the ass, unite, which would not do so if thev were free to select as in the wild state. These two are widely dis- tinct si^ecies, sometimes even called genera, and there- fore the offspring is infertile ; but two closely allied species, such as two species of wolf, or of the fox, in a domestic state would probably not only unite but pro- duce indefinitely fertile offspring. In fact, it is almost certain that the dog was made by a mixture of several species of wolf, most, perhaps all, of them now extinct.* * " Origin of Races of the Dog." *' Annals and Magazine of Natural History," vol. xvii, p. 295. 1886. 218 EVIDENCES OF THE TRUTH OF EVOLUTION. On the other hand, it is not at all certain that the extreme varieties of dogs have not passed the limit of greatest attraction, and therefore of greatest cross-fer- tility, and that, if allowed free choice, as in Nature, they would not breed true, or tend to breed true, with their own kind, and intermediate kinds die out in the struggle for life. Law of Cross-breeding". — Before going any further in this discussion, it is necessary to bring out another point of extreme importance in the formation of vari- eties, both natural and artificial — a point which I be- lieve throws light upon the very significance of sex itself — I refer to the effect of cross-breeding. It is a curious and most significant fact that dif- ferent varieties, both natural and artificial, are, up to a certain limit, not onlv cross-fertile and cross-attract- ive, but even more so than mdividuals of the same variety. Long experience has shown that very close breeding of the same variety for a long time fixes the I'UiJ but iijeakens the stock, especially in fertility, while judicious crossing of varieties strengthens the stock, increasing its fertility, and especially producing plas- ticity or variaMlity. Therefore breeders, if they wish to preserve a valuable variety, breed close ; but, if they wish to make new varieties, cross-breed. But we have already seen that species are usually cross-sterile. There- fore there must be some regular law of increase to a maximum, and again decrease to zero. It is this law that I now wish to investigate. PROOFS EROM ARTIFICIAL PRODUCTION. 219 In the lowest animals and plants multiplication of individuals and the continuance of the kind are inde- pendent of sex, and therefore in such there may he no sex at all. The sexual elements are not yet differen- tiated. An individual divides itself into tAvo ; each grows to the original size and again divides into two, and so on, it may be indefinitely. In this lowest form of reproduction the individual is sacrificed to the kind, or else we may regard the kind as an extension of the individual, and reproduction as a modification of growth. But there are other sexless modes of reproduction, found in nearly all plants and many lower animals, in which the individuality is not sacrificed. The next step in the ascending scale is reproduction by hudding. In this case a bud is formed which grows into a perfect individual, and may remain attached to the parent stalk, forming together a compound individual, as in most plants and many lower animals, such as the coral; or it may separate and assume independent life, as in some plants and many lower animals. In still other animals, as in many hydrozoa, the budding function is relegated to a SjDCcial part, which thus becomes a re- productive organ. The next step is the placing of the budding organ, for greater safet}-, in an interior cavity. This is the case v/ith aphids. JSTow, why would not this be an excellent mode of reproduction for all ani- mals, man included ? Why was sex introduced at all ? There are very sufficient reasons, of many kinds, which may come up later ; but the fundamental reason, in 220 EVIDEN"CES OF THE TRUTH OF EVOLUTION". connection with evolution, is the funding of individual differe7ices iii a common offspring, thereby giving to the offspring a tendency to divergent variation. Now, non-sexual re^DrocLuction is ahsolute true breed- ing. The law of like j)roducing like is absolute. He- redity is all-powerful, and tendency to variation is nil. These modes of reproduction are in fact but a modifica- tion of growth and an extension of the individual. Evo- lution-changes in animals produced in this way only must be very slow, since the most powerful factor of evolution, viz., natural selection among divergent varie- ties of offspring, would be wanting. In the earliest times, therefore, before sex was yet declared, we may imagine that physical environment was the great and only factor of change. Sexual reproduction introduces the new ele- ment of variation of offspring from which Nature makes her selections ; and this element of variation is appar- ently the result of the union of diverse individuals, and the funding of these differences in a common offspring, and thus a double inheritance of individual character- istics from the parents and a multiple inheritance of the same from the ancestry. See, then, with this end in view, the pains Nature has taken to make the difference be- tween the uniting individuals and the diversity of inher- itance by the offspring as great as possible, and yet the gradual way in which she has accomplished it. As al- ready said, the lowest form of reproduction is that by fission. Next comes budding in any part indifferently. Next comes the relegation of the budding function to a PROOFS FROM ARTIFICIAL PRODUCTION. 221 particular part. This is tlie first appearance of a repro- ductive organ. Next comes the placing of this organ, for greater safety, within. Thus far all is non-sexual reproduction — all a modification of growth — an extension of the individual, like the propagation of plants by cut- tings and by buds. Then comes sexual reproduction in its lowest forms. It may be well to stop here, to show the entire differ- ence between this and non-sexual modes. The latter, we have seen, is only a modification of growth, an extension of the individual. Now, sexual reproduction is the op- posite of all this. Growth is a constant multiplication of cells. One cell is ever becoming two similar cells — or, if we call them individuals, one individual is ever becom- ing two similar individuals. But in sexual reproduction we have an exactly reverse process. Reduced to its sim- plest terms, sexual reproduction is the fusion of tivo di- verse cells, sperm-cell and the germ-cell, to form one cell, the ovule — literally, a diverse twain forming one flesh. In its higher forms it is the union of diverse individuals to bring about the same result. Instead of one cell be- coming two, it is two cells becoming one ; instead of one individual becoming two in the offspring, it is two indi- viduals becoming one in the offspring. But this great change was not brought about at once, but only in the most gradual manner. First, the sexual elements — sperm- cell and germ-cell — are separated, but in the same organ. Then the organs — spermary and ovary — are separated, but in the same, individual. This is the condition of self- 222 EVIDENCES OF THE TRUTH OF EVOLUTION. fertilizing hermaphroditism so common among plants and lower animals. Then comes cross-fertilizing her- maphroditism ; and Nature takes much pains and uses many ingenious devices to prevent self-fertilization and insure cross-fertilization. Now, for the first time, we have slight individual differences funded in a common offspring. Then, in order to absolutely forbid self-fertili- zation, and at the same time allow greater differences in the crossing individuals than could be attained in her- maphroditic individuals, the sex organs are separated in different individuals, and fertilization can only take place by voluntary union. Then, to insure the nnion of suitable individuals, and forbid the ban between unsuit- able, there are introduced sexual attraction and repulsion. Then, last of all, the difference between the two sex- individuals becomes greater and greater as we go up. It is conspicuous only in yertebrates and some insects, and very conspicuous only in birds and mammals. We see, then, as we go up the taxonomic, and undoubt- edly also the phylogenic series, that there is a cross- breeding of more and more diverse individuals, a funding of more and more divergent characteristics in a common offspring. Why is this ? I answer, for the sake of bet- ter results in the offspring. This is abundantly shown by direct experiment. In hermaphroditic plants in which there may be either self-fertilization or else cross-fertiliza- tion with other individuals of the same species, the latter produces better results in number and vigor of offspring. But there are other advantages, more difficult to prove PPwOOFS FROM ARTIFICIAL PRODUCTIOX. 223 but none tlie less certain, and of the greatest importance in evolution : First, as already stated, complexity of in- heritance, like complexity of composition in a chemical substance, gives instability to the embryo, and thus lia- bility to variation in the offspring; and this in its turn furnishes the material for selection of the fittest. Again, it seems to me that there is a direct tendency to improve the offspring by a sort of struggle in the embryo among the various qualities inherited from both sides, and a survival of the best and strongest — a sort of pre-potency of strong qualities. Can divergence of uniting individuals and the fund- ing of diverse characteristics go any further ? It may. The differences of the unitinsr individual mav be still fur- ther increased, and the resulting offspring still further improved by the cross-breeding of different varieties of the same species, for we thus add varietal differences to sexual differences in the uniting individuals. It is well known that too close breeding, or consanguineous breed- ing, or breeding in and in, as it is variously called, if continued long, has a bad effect on the offspring, weaken- ing the stock, while judicious crossing of varieties w^ithin certain limits of difference has a good effect, strengthen- ing the stock and increasing its fertility. It probably does so in two ways : one direct, by funding many diverse qualities from both sides, and the survival in the off- spring of the strongest and best ; the otlier indirect, by giving plastirAfy, instability to the embryo, and varia- bility to the offspring, and therefore abundant material 11 22i EVIDENCES OF THE TRUTH OF EVOLUTION. for tlie operation of selection, either bj man or by Na- ture. We said, " within certain limits of difference." If the difference is extreme, as in extreme varieties and races, then the effect becomes again bad, and more and more so as the limit of specific difference is approached ; at which limit at last Nature shuts down and forbids the bans. Thus, then, there is in cross-breeding a regular law of effect, increasing to a maximum and again decreasing, which may be gra23hically represented by a curve (Fig. 69). In this figure tlie horizontal line represents the or- FiG. 69. dinary level of the type ; distances on this line represent differences, individual, varietal, or specific ; ordinates above or below represent the effect, good or bad, of cross- ing. Thus s s' represent two species,%nd the line between represents their specific differences ; r r' represent differen t races or permanent varieties ; v v' two strong varieties ; d cV ordinary individual differences ; c c' close resembling or consanguineous individuals. The undulating line rep- resents the effect of crossing these various kinds. It is seen that *^ in-and-in breeding," c c', produces bad effect (negative ordinates) ; breeding of ordinary individual differences, dcT, keeps the stock at the ordinary level — in its typical form ; crossing two strong varieties, v v', pro- duces maximum good effect (positive ordinates) ; crossing PROOFS FROM ARTIFICIAL PRODUCTION. 225 decided races produces again bad effects, which become infinitely bad as we approach species, s s'.* It is generally admitted that long-continued very close breeding has a bad effect. Even in plants, Darwin has shown that cross-fertilization has better effect than self- fertilization, this last being of course the closest possible breeding. But it is probable that the principal bad effect is not on the stock but on the process of evohttion. Very close breeding weakens the stock, ordinary breeding of individual differences maintains the stock at the or- dinary level and fixes it. Cross-breeding of varieties strengthens the stock, and also (and this is its main advantage) produces 23lasticity in the stock, gives rise to strong divergent variations, or even sports, and thus be- comes a main agent in evolution. It is j^robable, more- over, that the higher the function the more sensitive is it to these effects of breeding. Therefore, the effect is great- er in man than in any other animal. It is true that many have doubted the bad effect of close breeding in man, and have brought forward formidable statistics to substan- tiate their position ; but these doubtless take no account of the most imj)ortant function, the psychic, and espe- cially the most important element in every function, so far as evolution or j)rogress is concerned, viz., plasticity or capability of progressive improvement. The tendency of consanguineous breeding, or even the breeding of per- " Mr. Galton (" Nature," August 26, 1886) has used a diagram simi- lar to the above (which I first used in 1879) to illustrate the law of sexual attraction and repugnance. 226 EVIDENCES OF THE TRUTH OF EVOLUTION. sons of like character and experiences, as in an isolated community, is, if not to deteriorate the physique, at least to fix, stereotype the character, and thus to check social progress. Contrarily, the crossing of Yarieties of the same race seems not only to strengthen but, by the diverse inheritance, to produce plasticity of character and ca- pacity for progress. But the difference between the pri- mary races seems too great for crossing with advantage. Some degree of sexual repugnance which undoubtedly exists between the primary races is the psychical sign of this fact.* If, now, we go back to what we said before taking up this subject of the effect of cross-breeding, we at once see that there is an apparent flaw in all our reasonings. If close in-and-in breeding produced better and more nu- merous offspring than cross-breeding between slight va- rieties, then, indeed, such varieties would be preserved, and increase in divergence from generation to genera- tion until they became species. Or, in any case, if, in any way, divergence could reach the point of extreme varieties or races, or what are called sub-species, then commencing cross-sterility Avould complete the separa- tion, and thus form true species. But how can the pro- cess of progressive divergence begin, when slight varie- ties are even more fertile by cross-breeding than by close breeding ? Is it not evident that, with every generation, * This subject is more fully discussed )3y the author in an article en- titled " Genesis of Sex," in " The Popular Science Monthly," vol. xvi, p, 167, 1879. PROOFS FROM ARTIFICIAL PRODUCTIOX. 227 the slight Yarieties would cross-breed with one another and with the parent stock, and thus all varietal differ- euces would be funded into a common stock, and the type would be preserved unchanged ? This, as already pointed out (p. 76), has always been the chief difficulty in the way of imagining how varieties can grow into spe- cies ; and the difficulty is only increased by our discus- sion of the law of cross-breeding. Xow, just here, Dr. Romanes's most important and prolific idea comes to our help, and, as it seems to us, completely solves the diffi- culty. According to Dr. Romanes, no organ is so subject to variation as the reproductive, and this in no resjoect so much as in degrees and kinds of fertility — we might almost say so subject to freaks of cross-sterility. Now, suppose we start with any well-defined species in a state of nature. With every generation there are many slightly divergent individual varieties, some greater and some less ; but these are all immediately swamped by crossing with one another and with the parent stock, and the species remains unchanged. But suppose among these divergent variations there arise, from time to time, some which affect the reproductive organs in such wise that the variety, though perfectly fertile with its own kind, is infertile, or imperfectly fertile, with other varieties, and especially with the parent stock. The change may be only in the time of flowering in plants, or season of heat in animals, or it may be actual in- fertility in sexual union. Right here we have the be- 228 EYIDEXCES OF THE TRUTH OF EVOLUTION. ginning of a new species. The variety is sexnallv iso- lated from the parent stock by cross-sterility, and therefore all its peculiarities, however trivial, are pre- served by true breeding. Cross-breeding is necessary to make species, but true breeding preserves them. Cross- breeding tends ever to make varieties, but immediately destroys them again. This constant forming and swamp- ing, separating and again merging of varieties, like mixing of dough, makes the whole mass (stock) more and more plastic and subject to variety. This plas- ticity finally gives rise to varieties of the kind which produces specie3 by sexual isolation. By continued merging the centrifugal forces continually increase, but are continually repressed by crossing, until finally vari- eties break away to form species. 'Now it IS easy to see, from this point of view, why artificial varieties are cross-fertile. It is because in artificial breeding we are intent only on making vari- eties in form, size, color, etc., and not at all on making any characterized by cross-sterility with the parent stock. Cross-sterility with the parent stock, or with other varieties, would be of no advantage, because we control the breeding, and can breed true if we desire. Sexual isolation is not necessarv, because we can use physical isolation. On the contrary, such cross-sterility would be a positive disadvantage to the breeder, by limiting the range of his experiments just where they would be most prolific in making new varieties. Hence, as might be expected, all domestic varieties are cross- PROOFS FROM ARTIFICIAL PRODUCTION. 229 fertile, unless it be the extreme varieties, which may, ill some instances, have passed the limit of greatest fertility. If this idea be true, then species which have origi- nated in the same locality ought to be always cross- sterile, but species which have grown up apart, in widely separated geographical regions, ought to be sometimes cross-fertile, because they were isolated by physical not by sexual barriers. Such, Dr. Romxanes thinks, is a fact. It is, however, a very important point, which ought to be carefully investigated. We say ''sometimes.^'' It is probable that mo:t geographical species also are cross- sterile ; for, although the isolation by cross-sterility of slight varieties be the main cause of the origin of species, yet a species formed by isolation of any other kind will gradually become cross-sterile with other species. Although cross-sterility be the main cause of divergence, yet divergence beyond a certain limit, however caused, will bring about cross-sterility, because the reproductive organs will i3artake of the general change going on in every part. Application. — Suppose, then, a species breeding natu- rally in a wild state. Individual varieties are constantly being formed and again funded back into the common stock by cross-breeding. If the varieties thus formed be decided, the cross-breeding will strengthen the stock, and especially will preserve and increase its plasticity or tendency to variation. Finally, among the widely di- vergent varieties there is one affecting the reproductive 230 EVIDENCES OF THE TRUTH OF EVOLUTION. organs of several individuals in such wise that they are infertile, or imperfectly fertile, with the parent stock, though perfectly fertile among themselves. These form a new species, which continue to increase indefinitely. Ohjection answered. — This view completes the answer to an objection which is often made to evolution : *' If natural sj)ecies are formed by transmutation, why is it we do not find intermediate links ? Why is not organic nature made wp only of individual forms, shading in- sensibly into each other in such wise that classification becomes a mere device to handle more conveniently complex material ? Why is it that groups, especially species, are marked out with hard and fast lines ?" We have heretofore answered this by saying that inter- mediate forms are eliminated. So they are, but how ? Dr. Romanes's idea of physiological selection largely answers this. It is by the funding of ordinary varie- ties into a common parental stock by crossing, and separating specific varieties by cross-sterility. Thus the organic field is broken up into points about which variations oscillate. As every mass of matter, when closely examined, is found to consist of aggregations about centers of cohesive attraction as discrete granules or crystals, and only exceptionally do we find a homo- geneous vitreous structure ; even so organic forms ag- gregate about points of sexucil attraction, and the whole mass consists of discrete species, and only exceptionally — i. e., in domestication — do we find insensible shad- ings. Now, species are the smallest aggregate of indi- PROOFS FROM ARTIFICIAL PRODUCTION. 231 viduals, as granules are of molecules. Species are more distinctly marked out by hard and fast lines than are other taxonomic groups only because they are the last, going downward, that are cross-sterile — because right here is the change from cross-sterility to cross-fertility. If this yiew be true, then in the same locality spe- cies ought to be always distinct and without shadings. If we find shadings at all, it ought to be in interme- diate geographical regions, where isolation is not sexual but physical. Now, this is exactly what we find to be the fact. hmumeraUe examples of such intermediate forms in i^itermediate geographical regions are now known, especially among birds and reptiles, and exam- ples have so increased in modern times, by closer study, that naturalists, especially ornithologists, have been com- pelled to resort to a trinomial nomenclature in order to designate these geographical sub-species.* If any further explanation is necessary, it will prob- ably be found in the following suggestions : 1. The number of individual varieties constantly being formed is almost infinite, but the number of places in nature is very limited. Now, among the in- finite number of slight individual varieties formed with every generation, the competitive struggle will be se- verest between those most nearly alike, because they are competitors for the same place. Only one kind suc- * For examples of this the reader is referred to Cope, " Bulletin of the National Museum," No. 1 ; and to Coues's " Key to North American Birds," last edition. 232 EVIDENCES OF TPIE TRUTH OF EVOLUTION. ceeds, viz., the fittest. Intermediate forms are, there- fore, exactly those which are eliminated in the most wholesale way. 2, Add to this the fact that, as soon as divergence, from whatsoever cause, reaches a certain point, sexual repugnance or cross-sterility, or both, come in to i^erpetuate and increase the separation already commenced. 3. Add to this, again, that migrations in higher animals, and involuntary dispersals in lower ani- mals and in plants, and the mingling together of dif- ferent faunas and floras, produces a still fiercer struggle for life, especially between natives and invaders, and thus great numbers of forms are destroyed ; all but the fittest are weeded out, and therefore the distinctness of the remainder is greatly increased. Periods of great changes of physical geography and of climate, and there- fore of wide and general migrations, are also periods of great weedings-out of unfit forms. Thus it happens that existing faunas and floras are little else than iso- lated remnants. To illustrate, again, by a growing tree : If all the buds of a tree lived and grew, they would soon become so numerous that they would together form a solid hemispherical mass, like a coral-head, with no room between for leaf or light or air. But ninety-nine one- hundredths of buds die in the strusfslo for lio^ht and air, and therefore the survivors are distinct growing points, widely separated from each other. Species are such extreme, but separated, twiglets of the tree of life. Objection. — But it will be objected, again : The twig- PEOOFS FROM ARTIFICIAL PRODUCTION. 233 points are, indeed, separate, but the twigs themselves must meet somewhere lower down, where they began to grow. Intermediate links may be w^anting noiv, but they must, of course, have existed once — i. e., in pre- vious geological times, and therefore ought to be found fossil. In distribution in space or geographically, organic kinds may be marked oS by hard-and-fast lines, but, if their derivative origin be true, in their distribution in time or geologically, there ought to be many examples of insensible shadings between them. In fact, if we only had all the extinct forms, the organic kingdom, taken as a whole and throughout all time, ought to consist not of species at all, but simply of individual forms, shading insensibly into each other, like the colors of the spectrum, and our classification ought to be a mere matter of convenience, having no counterpart in nature. But this is not the fact. On the contrary, the law of distribution in time is apparently similar in this respect to the law of distribution in space, already given (page 169). As in the case of contiguous geographical faunas, the change is apparently by substitution of one species for another, and not by transmutation of one species into another. So also in successive geological faunas, the change seems rather by substitution than by trans- mutation. In both cases species seem to come in sud- denly, with all their specific characters perfect, remain substantially unchanged as long as they last, and then die out and are replaced by others. Certainly this looks much like immutability of specific forms, and 23i EVJDENCES OF THE TRUTH OF EVOLUTION. supernaturaHsm of specific origin. We have, we be- lieve, satisfactorily explained this in the case of geo- graphical distribution (page 201), but how can we ex- 13lain it in the case of geological distribution ? Answer. — 1. The reason for this, given by Darwin and other evolutionists, is the extremely fragmentary character of the geological record. If the existing faunas and floras are but isolated remnants, the rest having been destroyed by migrations and conflicts, how much more are fossil faunas and floras but fragmentary remnants, the rest having been lost, partly because never preserved, and partly by destruction of the record ! If from this cause existing species are widely separated, how much more ought we to expect to find fossil species distinct and widely separated ! This is undoubtedly in most cases a true and suffi- cient answer, yet we think the fragmentariness of the geological record has been overstated. While it is true that there are many and wide gaps in the record ; w^iile it is true, also, that even where the record is continiious many forms may not have been preserved, yet there are some cases, especially in the Tertiary fresh-water de- posits, where the record is not only continuous for hun- dreds of feet in thickness, but the abundance of life was very great, and the conditions necessary for preser- vation exceptionally good. In such cases the number of fossil species found on each horizon seems to be as great as in existing faunas over equal space. The rec- ord in these cases seems to be continuous and without PROOFS FROM ARTIFICIAL PRODUCTION". 235 break, and crowded with fossil forms ; and yet, although the species change greatly, and perhaps many times, in passing from the lowest to the highest strata, we do not usually, it must be acknowledged, find the gradual transitions we would naturally expect, if the change v/ere effected by gradual transformations. The incom- pleteness of the record, therefore, although a true and important cause, is not the whole cause. In further and completer answer to this greatest of all objections, we will throw out the following sug- gestions : 2. We must remember that considerable latitude is allowed by the anti-derivationists to variation of species ; so much so, indeed, that it is often difficult to draw the line between well-marked varieties and closely-allied spe- cies. Now, according to the derivationist, these strong varieties, breeding usually true, are naught else than commencing species. 3. On every side and everywhere, both m existing faunas and in fossil forms, but especially in the latter, we find innumerable examples of transitions, or inter- mediate forms, between all the Mglier groups, such as genera, families, orders, and classes. It is, m fact, by means of these that the great law of differentiation from generalized types has been established. It is, therefore, only between species that such intermediate forms are rare. 4. But even between species such intermediate forms, though rare, have been pointed out, both in existing 236 EVIDENCES OF THE TRUTH OF EVOLUTION". and in extinct faunas. But the opposition contend that, in all such cases, the previously supposed species are only varieties. We have already (page 61) spoken of the obvious fallacy involved in this position. Species are fii^t defined as forms distinct and without inter- mediate links, and then we are challenged to find such links ; and when, with much labor, we find them, they say the supposed species are not species, but only vari- eties. But there are some cases in wliich this subterfuge will not do. There are cases in which the transitions are between forms so extreme that they can not, by any stretch of the term, be called varieties. "W'e will select and dwell upon but one striking example, viz., the fossil forms of the Tertiary fresh-water deposits of Steinheim. In Wiirtemberg, near the little village of Steinheim, are found certain strata of sand and lime, which are evi- dently deposits from a small lake of Tertiary times. The deposits are extremely rich in fossil shells, especially of the different species of the genus Planorbis. As the de- posits seem to have been continuous for ages, and the fossil shells very abundant, this seemed to be an excel- lent opportunity to test the theory of derivation. With this end in view, tliey have been made the subject of ex- haustive study by Hilgendorf in 1866,* and by Hyatt in 1880. f In passing from the lowest to the highest strata * " Monatsbericlit d. k. Preuss. Akademie d. Wisscnschaft zu Berlin," for July, 1866. \ "Genesis of Tertiary Species of Planorbis at Steinheim." A. Hyatt, Anniversary Memoir of the Boston Society of Natural History, 1880. PROOFS FROM ARTIFICIAL PRODUCTION. 237 the species change greatly and many times, the extreme forms being so different that were it not for the inter- mediate forms they would be called not only different species but different genera. And yet the gradations are so insensible that the whole series is nothing less than a demonstration, in this case at least, of origin of species by derivation with modifications. The accompanying plate of successive forms (Fig. 70), which we take from Prof. Hyatt's admirable memoir, will show this better than any mere verbal explanation. It will be observed that, commencing with four slight varieties — probably sexually isolated varieties — of one species, each series shows a gradual transformation as we go upward in the strata — i. e., onward in time. Series I branches into three sub-series, in two of which the change of form is extreme. Series IV is remarkable for great increase in size as well as change in form. In the ]}late we give only selected stages, but in the fuller plates of the memoir^ and still more in the shells themselves, the subtilest gra- dations are found. This case is striking, partly because it is a very favor- able one, but mainly because it has been so carefully studied. There can be no doubt that equally careful study would reveal the same transition in many other cases. Nor are such transitions confined to the lower forms of life, though they are probably more abundant there. According to Cope, the nicest gradations may be traced between some of the extinct mammalian species so abundant in the Tertiary deposits of the West — espe- 238 EVIDENCES OF THE TRUTH OF EVOLUTION. Fig. YO. — Transformations of Planorbis (after Hyatt). Soies IV. 1, PI. levis: Undorf. 2, PI. Steinheimensis ; 3, tenuis-Stein- heimensis ; 4, tenuis ; 5, discoicieus ; 6, trochiformis-discoideus ; 7, trochiformis : Steinheim. Series III. 8, PI. levis: Undorf. 9, PI. oxystomus ; 10, suprcmus ; 11, supremus var. turrita : Steinheim. Series II. 12, PI. levis: Undorf, 13, PI. crescens-parvus ; 14, 15, cres- cens: Steinheim. Series I. Sub-series 3. 16, PI. levis: Undorf. 17, PI. minutus-levis ; PROOFS FROM ARTIFICIAL PRODUCTION. 239 18, minutus; 19, 20, triquetrus : Steinheira. Sub-series 2. 21, PI. minutus ; 22, 28, denudatus-minutus ; 24, denudatus var. distortus : Steinheim. Sub-scries 1. 25, PI. costatus-minutus ; 26, costatus ; 27, 28, costatus var — : Steinheim. The specimens from Undorf all belong to an older Tertiary period than that at Steinheim. cially between the species of the extinct generalized fam- ily of Oredontidce.'^ The same is probably true of the many extinct species of the horse family. It is interesting to observe that the details of the pro- cess of change in the forms of Planorhis are in accord with Dr. Eomanes's views. The change does not seem to have been uniform but somewhat paroxysmal. The forms seem to remain stable for a long time, and then a few break into several different forms, while the more rigid die out. It is as if cross-breeding had kept the type true, but at the same time increased its tendency to variation, until finally one or more varieties became sexu- ally isolated and thus formed new species. 5. But still the question remains : Why are transi- tional forms rare in all cases, esj^ecially between species — so rare that they are eagerly sought and highly prized ? I believe that the true reason of this is that the steps of evolution are not ahvays uniform. Nearly all evolutionists have assumed and even in- sisted on uniformity, as the opposite of catastrophism and of supernaturalism, and therefore as essential to the idea of evolution. They say that the constancy of the * In a letter to the author, dated February 13, ISSY, Prof. Cope says : "Such transitions of species are clearly indicated in the Oreodontidce, where such different forms as 0. gracilis and 0, Culbertsoni are connected by intergradations." 240 EVIDENCES OF THE TRUTH OF EVOLUTION. action of the forces of change necessitates the uniformity of the rate of change. But, in fact, this is not always nor even usually true. Causes or forces are constant, but phenomena everywhere and in every department of Ma- ture are paroxysmal. The forces producing storms and lightning, and volcanoes and earthquakes, are or may be constant ; yet the phenomena are in the highest degree paroxysmal. Wherever in nature we have a constant force and a strong resistance, we find more or less parox- ysmal action. For this reason the wind blows in puffs, the friction of wind on water produces waves, water run- ning in small pipes issues in pulses. The reason is ob- vious, as may be seen by the following examples : Sup- pose lifting forces witliin the earth are resisted by crust- rigidity. The forces accumulate uniformly until the resistance gives way, and suddenly we have an earth- quake. Water running with great resistance in small pipes is checked, but soon accumulates additional force, which overcomes the resistance, only to be again checked, and so on, and therefore runs in pulses. Now, the course of evolution of the whole earth may be likened to such a current ; there are forces of movement and forces of re- sistance — progressive forces and conservative forces. The progressive force is accumulative, the resisting force is constant. Thus, in all evolution or history, whether of the earth or of society, there are periods of comparative quiet, during which the forces of change are gathering strength, and periods of revolution or rapid change, during which these forces show themselves in conspicuous effects. PROOFS FROM ARTIFICIAL PRODUCTION. 241 Now, that there have been such periods of rapid revo- lutionary change in the history of the earth, there can be no doubt. The history of the earth is marked by periods of comparative quiet, during which life was exception- ally abundant and jorosperous, and change of organic forms slow and uniform — separated by periods of dis- turbance, revolution, rapid changes of physical geogra- phy and climate, and consequently of comparatively rapid and sweeping changes in organic forms. These form the division-lines between great eras of the earth's history, and are alv/ays marked by extensive unconformity of the strata, showing the changes of physical geography above spoken of, and by apjiarently sudden and sweeping change in life-forms, showing the great changes of cli- mate and other physical conditions. Unfortunately, in all cases of unconformity of strata, there is, of course, a break in the continuity of the record ; and when the un- conformity is very general a portion of the record may be irrecoverably lost. The consequence is, that there is an apparent break also in the continuity of life-forms. It looks, at first sight, like wholesale extermination of old and recreation of new forms. But undoubtedly the break in the continuity of life is apparent only, as is shown by the loss in the record. If we could recover the whole record, as indeed we sometimes do, we should find in all cases that there is no break in the continuity of evolu- tion, but only more rapid rate of change at these times. But to this cause of rapid rate of j^rogress — i. e., change of physical environment — we must add change of organic 242 EVIDENCES OF THE TRUTH OF EVOLUTIOK environment induced bj the physical. We have already seen (p. 179) that extensive changes in physical geogra- phy and climate are always accompanied by wide migra- tions and dispersals of species, the mingling of faunas and floras, and the severer struggle for life, and the sweeping weeding-out of all but the fittest, and the change of these latter, making them still fitter. These two causes of rsi])\d change, viz., change of climate and migrations, together with the loss of record, we believe completely account for those sweeping changes, not only of species but even of genera, families, and orders W'hich characterize the passage from one great era to another. But this does not yet explain the apparent disconti- nuity between consecutive sj^ecies in the same locality in continuous, conformable strata, or the rarity of transi- tional forms when one species takes the place of another in an ajoparently continuous record. In such continuous deposits the successive faunas do indeed gradate insensi- bly into one another, but apparently as in contiguous geo- graphical regions (p. 200) by substitution, not by trans- mutation. How shall we explain this ? On this point I throw out some suggestions : 1. In the modification of species, too, as well as in other pro- gressive changes, we may imagine two forces operating, one progressive, the other conservative — tlie one external, the other internal. The external progressive force con- sists of all the factors of change already mentioned, the internal conservative is the law of heredity, of like pro- ducing like. A changing environment tends continually PROOFS FROM ARTIFICIAL PRODUCTION". 243 and increasingly to change of organisms, but change is resisted by heredity, which tends to adhere, within nar- row limits, to the same form. But since the external- force or tendency to change increases constantly — since the discord between the environment and the organism becomes ever greater, there must come a time when either the species is destroyed, or else the resistance of heredity gives way, and rapid change takes place. The alternative is presented to the species to transform or perish ; and in one or perhaps in two or three generations we have an amount of change which, under other circumstances, might take a hundred generations to accomplish. These rapid changes are in fact exactly what in artificial varie- ties we call sports. We do not know all the conditions which determine sports in domestication, and still less what determines large and widely-divergent variations, and therefore rapid origin of many divergent species, in geological history. But one thing seems probable, viz., that, when a species begins to change, it continues to change easily and in many directions. When resistance gives way it takes some time, many generations, for he- redity to gather force again. Hence, young species are plastic, fluent, because heredity, on any one point, has not yet accumulated. But as soon as a stable form is again reached, then, by accumulating a fund of heredity, the form tends to become more and more rigidj until often it becomes too rigid to yield to modifying influ- ences, and therefore becomes extinct. By far the greater number of species do thus become extinct and leave no 24:4: EVIDENCES OF THE TRUTH OF EVOLUTION. progeny, while the few more plastic forms are modified in several directions, and the number of forms may, after a little time, be undiminished or even increased. 2. As to the catise of rapid changes of form during revolutionary or critical periods in the earth's history, Brooks has introduced an idea which is very suggestive, and deserves serious attention. We have above spoken of the progressive element as external. Brooks regards both elements as internal, and represented by the two sexes. The male represents the progressive, the female the conservative element. The one tends to divergent variation, the other to fixity of type by heredity. I think we will all admit that, as a general rule, in man (and probably all the higher animals) the male is more highly differentiated into many divergent forms — the female is more like the type-form of the species. In man, the male is certainly more diversified in form, in expression, and in character. If they have the keenest ear for musical pitch, they are also most often music- deaf ; if they have the sharpest jDcrception of color, they are also most often color-blind ; if among them we find the brightest intellects, we also find the dullest and most stupid ; if there are among them more geniuses, so, also, there are more cranks. The same is also, prob- ably, true of other animals, in proportion to their grade of organization. The operation of these two equally necessary elements is well shown in every advancing society. The initiative of every movement, in all direc- tions, good or bad, is determined by the male ; the con- PROOFS FROM ARTIFICIAL PRODUCTION". 245 servation of whateyer balance of good there may be, seems to be mainly by the female. The male tries all things, the female holds fast that which is good. By the one society gains a little in each generation ; by the other the gain is conserved and made a new point of departure. The one is ever building hastily a scaffold- ing and platform ; the other ever consolidating into a permanent structure. Now, according to Brooks, what is true in the plane of social progress is true also in the lower plane of organic evolution. In sexual union, and in the resulting offspring, the sperm-cell is the element which tends to divergent variation, and the germ-cell to fixity of type, through heredity. In arti- ficial breeding, then, we ought to make new varieties by proper use of the sire ; we ought to preserve them true by proper mauagement of the dam. But, again, it is believed that in many lower ani- mals, especially insects, the high-feeding of the mother, and consequent good condition of the ovum, tends to the production of female offsjoring. It seems almost certain that, in butterflies, the sex is not yet declared in the caterpillar stage. According to the careful ex- periments of Mrs. Treat, "^ if the caterpillars be well fed, they become female butterflies ; but, if poorly fed, they make males. One purpose of this provision of Kature is, doubtless, to provide for the greater draught on the vitality of the female in reproduction. * "American Naturalist," ISYS; "Popular Science Monthly," June, 1873. 246 EVIDENCES OF THE TRUTH OF EVOLUTION. 'Now for the application. In good times in the his- tory of a species, when everything is prosperous, external conditions are favorable, and food is abundant, females are in excess, and individuals are greatly multiplied. Under these conditions, evolution would be slow and uniform. But in Md times in the history of a species, when external conditions were unfavorable, not only Vfould there be excess of males, but these, through the influence of the changing environment, as well as through the dominance of the male element, would be more than usually varied in character. Among the strongly diver- gent varieties thus formed, the fittest — i. e., those most in accord with the changing environment — would sur- vive and leave offsioring partaking of their character. We have already repeatedly said that the severer pressure of a rapidly-changing environment determines corre- sjoondingly rapid changes in organic forms. It may do so in many ways ; but, according to Brooks, one of the most important ways is by determining an excess of the male element. In brief, then, the causes of rarity of transitional forms among fossils are — 1. The change being, for the reasons given, comparatively rajiid, the numher of gen- erations between consecutive species are few, perhaps only one. 2. Times of rapid change are also times of unfavorable conditions, and therefore the number of individuals in each generation is small, and all the smaller — in Brooks's view — because of the fewness of females. AVhen we remember that fossils are but a PROOFS FROM ARTIFICIAL PRODUCTION. 2iT small fraction of the actual faunas and floras of the time, surely these two causes go far toward explaining the rarity of links between species. 3. Add to these the existence of periods of wide-spread changes in physi- cal geography and climate, and consequent wide migra- tions and dispersals of species, and we sufficiently ac- count for those sweeping changes in species, genera, families, and orders, which mark the limits of the great eras, and which are made still more abrupt, and appar- ently supernatural, by the loss of record at these times.* Objection. — There is still one more objection which will be made. We have drawings of plants, animals, and men, by Egy2:»tian artists, who lived at least three thousand years ago, and the species of the one and the races of the other are still the same. Still better, we have among the wrappings of Egyptian mummies the very plants themselves, leaves and flowers perfectly preserved, and even colors almost perfect. Yet the species are exactly the same as grow in Egypt to-day. If species are made by gradual transmutation, surely there ought to have been some change in three thou- sand years. Answer. — It may be well to note that this apparent permanence is true of races of men as well as of spe- cies of animals and plants. But the very men who * For a fuller development of this subject the reader is referred to an article by the author, entitled " Critical Periods in the History of, and thair Relation to, Evolution " (" American Journal of Science," vol. xiv, p. 99, 1877). 12 248 EVIDENCES OF TEE TRUTH OF EVOLUTION". insist on permanence of sj^ecies are equally insistent on the yariability of yarieties and races. The objection, therefore, proves too much. We shall not insist on this, however, because as derivationists we reirard races as naught else than commencing species, and therefore subject to the same laws. We ai'e not striving for tri- umph in debate, but only for truth. The true answer will, we believe, be found among the following sugges- tions : 1. Three thousand years seems a long time in human history, but in geological history it is but a day. This, the usual answer, is no doubt a true one, but hardly, we think, sufficient. When we remember the enormous change whicli has taken place in faunas and floras since the end of the Tertiary, if change still continues at the same rate, surely it ought to be distinctly perceptible in three thousand years. 2. But we must remember that such changes are usually more or less paroxysmal ; not, indeed, so sud- den as to break the continuity of life, but far more rapid at some times than at others. The last critical or revolutionary period of rapid change was the Glacial epoch. Since that time — i. e., during the human pe- riod — a new equilibrium has been established, and the changes in organic forms have been very slow. 3. Remember, again, that in evolution all sjiecies do not change. On the contrary, most become rigid, and either remain unchanged, almost indefinitely, or else die out and leave no descendants. Only the more PROOFS FROM ARTIFICIAL PRODUCTION. 249 plastic forms change into other species, but usually into several other s^DCcies, and thus the number of forms may be undiminished, even though the larger number of old forms leave no descendants. It is true, there- fore, of this as well as of other epochs, that the greater number of species are permanent. 4. It is not impossible — indeed, it is in exact ac- cordance v\^ith the laws of evolution — that organic forms are more permanent now than ever before. Evolution is a growth ; the forces of growth must exhaust them- selves. Evolution proceeds by constant differentiation and specialization, but extreme specialization always arrests evolution. In ontogenic evolution, for example, cell-structure becomes more and more specialized, but also thereby more and more rigid, and, when special- ization is complete, evolution stops, and cell-forms are permanent. It is this which limits the cycle of every evolution. So is it precisely wdth evolution of the or- ganic kingdom, except that the cycle is much longer. Here, also, every step is by specialization, and yet spe- cialization fixes the form, and finally arrests the advance on that line. Thus, throughout the whole geological history of the earth, the larger number of forms, by specialization, become rigid and perish, while the fewer, more generalized, and more plastic forms take up the march and carry it forward a step, only to be them- selves specialized and fixed. If we compare, again, to a tree : each twig finishes its growth, flowers, fruits, and dies ; other buds take up the grow^tli and carry it for- 250 EVIDENCES OF THE TRUTH OF EVOLUTION. ward. By specialization the highest condition of a cer- tain form of life is attained, but other possibilities are shut off. Extreme specialization is the flowering and fruiting — the end and completion of twig-life. ISTow, obviously, this specialization and respecialization can not go on forever. When it is complete in every direc- tion it must cease, and forms become permanent, or else perish. When it flowers it must die. Now, is not the advent of man in many ways a sign of the completeness of organic evolution ? Certain it is that with man there begins an entirely new form of evolution. Certain it is that with man evolution is transferred from the organic to the social plane, from the material to the psychical. Certain it is that the forces, the conditions and results of this evolution, are wholly different from those of the other. In organic evo- lution the organism must conform to the environment ; in human evolution the environment is made to conform to the wants of the organism. The one is unconscious and involuntary, passive under the dominating laws of Nature ; the other is conscious, voluntary progress toward an ideal, ly the use, among other means, of the laws of Nature. The one is by change of external form — i. e., change of species — the other by change of brain-struct- ure. Now, does not the commencing of the cycle of this new evolution imply the closing of that of the old ? The two may overlap somewhat now, but it is evident that, when the cycle of human evolution culminates, when highly civilized man shall have taken possession PROOFS FROM ARTIFICIAL PEODUCTIOX. 251 of the whole earth, the whole organic kingdom must be readjusted to his wants. All organic forms must be either domesticated or destroyed. Organic forms will no longer be modified by natural but wholly by arti- ficial selection. There are many other supposed objections which have been urged, but these are mostly not objections to evo- lution, but only to some special theory of CTolution — Darwinian, Spencerian, Lamarckian, or other. Origin of Beauty. — For example, it has been urged that natural selection can only account for useful struct- ures ; but 'beauty is as universal and as conspicuous in nature as use. In many cases Darwin has shown that beauty is useful, and in such cases it is, of course, seized upon by selection and intensified. Thus, the gorgeous coloring of birds and insects is largely due to sexual selection. Beauty is attractive, and therefore the most beautiful i^revail in securing reproductive op- portunities. This character is, therefore, perpetuated in the offspring, and intensified from generation to gen- eration. But, of course, this can apply only to higher animals, in which the sexes are separate and sexual union voluntary. It can not apply to self-fertilizing hermaphrodites ; and yet in these, also, we often find the most gorgeous coloring. Again, Darwin has very ingeniously and successfully exi^lained the case of the beauty and fragrance of flowers of hermaphroditic plants by another principle, viz., that of insect-selection. In- 252 EVIDENCES OF THE TRUTH OF EVOLUTION. sects are attracted by the most showy and fragrant flowers, and thus become the means of carrying i:»ollen from flower to flower, insuring fertilization, and espe- cially cross-fertilization. The most beautiful and fra- grant flowers are most certain to be fertilized, and tiuis beauty and fragrance become useful to the jilant, and therefore are selected and intensified. These and many other cases of beauty may doubtless be explained by showing that it is useful ; but beauty wliich is without any use can not be exjilained by nat- ural selection. Xow, as already said, the most gorgeous beauty is lavishlv distributed even among the lowest animals, such as marine shells and pol3'p3, where no such exj^lanatiou is possible. The process by which such beauty is originated and intensified is wholly unknown to us. Incipient Organs. — Again, Mivart has drawn attention to another difficulty in the way of natural selection as an explanation even of useful organs. Darwin does not, of course, attempt to account for the origin of varieties. As we have already seen, he assumes diyer£:ent variation of offspring as the necessary material on which natural selection operates. He who shall explain the origin of yarieties will have made another great step in completing the theory of evolution. But not only does not natural selection explain the origin of varieties, but neither can it explain the first steps of advance toward usefulness. An organ n-iust be already useful before natural selection can take hold of it to improve it. It can not make it PROOFS FROM ARTIFICIAL PRODUCTION". 253 useful, but only more useful. For example, if fins com- menced as buds from the trunk, it is difficult to see hoAv they could be of any use, and therefore how they could be improved by natural selection until they were of con- siderable size, and especially until muscles were developed to move them. Until that time they would be a hin- drance to be removed by natural selection, instead of a use to be preserved and improved. It would seem that all organs must have passed through this incipient stage, in which their use was prospective. Much that is very interesting might be said on these and similar points of difficulty, but all this lies entirely aside from the scope of this work. As already said, these are not objections to evolution or derivation, but only to Darivinism, or any other special theory, as a sufficient exiiilanation of the process of evolution. They only show that we do not yet fully understand this process ; that there are still other and perhaps greater factors of evolu- tion than is yet dreamed of in our philosophy. In the foregoing chapters on special evidences, and especially in the last two, the reader will observe many points of doubt, discussion, and difference of opinion. Let it not be concluded on that account that the laic of evolution is still in the region of uncertainty. It can not be too strongly insisted on that the fact of evolution as a universal law must be kept distinct from the causes, the factors, the conditions, the processes, of evolution. The former is certain, the latter are still imperfectly un- derstood. P AET III. THE RELATION OF EVOLUTION TO RELIGIOUS THOUGHT. CHAPTER L IN^TRODUCTORY. From what has preceded, the reader will i^erceive that we regard the law of evolution as thoroughly estab- lished. In its most general sense, i. e., as a law of con- tinuity, it is a necessary condition of rational thought. In this sense it is naught else than the universal law of necessary causation applied to forms instead of phe- nomena. It is not only as certain as — it is far more certain than — the law of gravitation, for it is not a con- tingent, but a necessary truth like the axioms of geome- try. It is only necessary to conceive it clearly, to accept it unhesitatingly. The consensus of scientific and phil- osophical opinion is already well-nigh, if not wholl}^, complete. If there are still lingering cases of dissent among thinking men, it is only because such do not yet conceive it clearly — they confound it with some special form of explanation of evolution which they, perhaps justly, think not yet fully established. We have some- times in the preceding pages used the words evolutionist or derivationist ; they ought not to be used any longer. Tlie day is past when evolution might be regarded as a 258 EVOLUTION x\ND RELIGIOUS THOUGHT. school of thought. "We might as well talk of gravita- tionist as of evolutionist. If, then, evolution as a law be certain, if, moreover, it is a law affecting not only one part of Nature — the organic kingdom — and one department of science — bio- logy — but the whole realm of Nature and every depart- ment of science, yea, every department of thought, changing our whole view of Nature and modifying our whole philosophy, the question presses ujion us, ^' What will be its effect on religious belief, and therefore on moral conduct ? " This is a question of gravest import. To answer it, however imperfectly, is the chief object of this work. Except for this, it would probably never have been undertaken. All that goes before is sub- sidiary to this. But I will doubtless be met at the very threshold by an objection from the scientific side. Some will say — because it is the fashion now to say — that as simple, honest truth-seekers, we have nothing to do with its effect on religion and on life. They say we must follow Truth wherever she leads, utterly regardless of what may seem to us moral consequences. This I believe is a grave mistake, the result of a reaction, and on the whole a wholesome and noble reaction, against the far more com- mon mistake of sacrificing truth to a supposed good. But the reaction, as in most other cases, has gone much too far. There is a true philosophic ground of justifica- tion for the reluctance with w^hich even honest truth- seekers accept a doctrine which seems harmful to so- INTRODUCTORY. 259 ciefcy. Effect on life is, and ought to be, an important element in our estimate of the truth of any doctrine. It is necessary for me to show this, in order to justify this part of my work. Relation of the True and the Good. — There is a ne- cessary and indissolnble connection between truth and usefulness. We all at once admit this connection in one direction. We all admit that a truth must eyentually have its useful application. It may not be noiv, nor in ten years, nor in a century, nor even in a millennium, but some time in the future it will vindicate its useful- ness. No truth is trivial or useless in its relation to human life, for man is a part of Nature, and his life must be in accordance with the laws of Nature. Every one admits this, but not every one admits the converge proposition, viz., that whatever doctrine or belief, in the long run and throughout the history of human advance- ment, has tended to the betterment of our race, must have in it an element of truth by virtue of which it has been useful ; for man's good can not be in conflict with the laws of Nature. Also, vvhatever in the long run and in the final outcome tends to the bad in human conduct, ought to be received, even by the honest trnth-seeker, with distrust as containinar essential error. The reason of this will now be further explained. Relation of Philosophy to Life.— There are three pri- mary divisions of our psychical nature, viz., sensuous, intellectual, and volitional or moral. There are three corresponding primary processes necessary to make a 2G0 EVOLUTIOi^ AND RELIGIOUS THOUGHT. complete rational and satisfactory philosophy : (1) There is first the instreamiiig of the external world through the senses, as impressions. These we call facts or phenome- na. (2) The elaboration of these facts within, by the i7i- tellect, into a compact, consistent structure. This we call knowledge. (3) The outgoing of this knowledge by the luill into the world as ri^ht or wise conduct. Now these three are all equally necessary. All these three portions of our complex nature are equally urgent to be satisfied.* But, unfortunately, scientific workers are too apt to think only 1 and 2 necessary — that true facts elaborated into consistent theory are all we need care for. Theo- logians and metaphysicians, on the other hand, seem to think only 2 and 3 necessary. They elaborate a theory consistent in all its parts, exquisitely woven in beautiful and delicate pattern, and apjiarently satisfactory in its aj^plication to the right conduct of life, but are less careful to inquire whether it is in harmony with facts derived from the senses. But, we repeat, all three are equally necessar}^ The first gathers the materials, the second constructs the edifice, the third, by use, by prac- tical application, tests whether it be a fit building to live in, whether it is constructed on sound architectural prin- ciples. The tendency of the olden time was to neglect the first, the tendency of the present time is to neglect the third. But we repeat with stronger emphasis that this third element is equally necessary. All admit that suc- * '' Reflex Action and Theism," William James, " Unitarian Review " fov November, 1881. INTRODUCTORY. 2G1 cessful application in art is tlie surest test of the truth of science. Now, social conduct is the art correspond- ing to our philosophy of life, aud therefore is the sure test of its truth. It follows, therefore, that unless all these three primary divisions of our nature are satis- fied by any doctrine, there must result an ineradicable confusion and discord in our psychical nature, and cor- dial acceptance is not only impossible but irrational. We insist ujion this the more because it has become the fashion in these latter days of dominance of science, to say that to inquire into effects on society is inconsistent with the scientific spirit, and unworthy of the honest truth-seeker. But, observe, I am speaking of effects on society only as a test of truth. I would not swerve a hair's breadth from absolute devotion to truth. It is necessary, indeed, to inquire into effects on society, but we must inquire only in the patient spirit characteristic of the truth-seeker. Whatever is really true will surely vindicate itself by its beneficence, if we will only wait patiently for final results. Evolution is no exception to this universal truth. It will surely vindicate its beneficence, but we must wait yet a little while — not very long. So much it was necessary to say in justification of the inquiry which constitutes this third part of our work. But, after this justification, the question returns with additional emphasis, '^ What will be the effect of the universal acceptance of the law of evolution on religious thought, and through this on the right conduct of life ?" 282 EVOLUTION AND RELIGIOUS THOUGHT. There can be no doubt that evolution, as a law affect- ing all science and every department of Nature, must fundamentally affect the whole realm of thought, and pro- foundly modify our traditional views of JNature, of God, and of man. There can be no doubt that we are now on the eve of a great revolution. But, as in all great revo- lutions, so in this, the first fears as to its effects are greatly exaggerated. To many, both friends and foes of Christianity, evolution seems to sweep away the whole foundation, not only of Christianity, but of all religion and morals, by demonstrating a universal materialism. Many are ready to cry out in anguish, '^Ye have taken away our gods, what have we more ? Ye have destroyed our dearest hopes and noblest aspirations, what more is left worth living for ?" But I think all who are at all familiar with the historv of the so-called conflict between religion and science will admit this is not Ihe first time this cry has been raised against science. They have heard this danger-cry so often that they begin to regard it as little more than a wolf-cry — scientiflc wolf in the religious fold. It may not be amiss, then, to stop a mo- ment to trace rapidly the main j^oints of this conflict — to discuss the various forms of this scientific wolf. First, then, it came in the form of the heliocentric theory of the ^axiMury_siistem. We once thought the earth the center of the universe, and so firm that it can not be moved. But science shows that it moves about the sun, and spins unceasingly on its axis. Every one has heard of the terror of the sheep produced by this dis- INTRODUCTORY. . 263 covery, and the nearly tragic results to the bold scientist. But now we look back with wonder that there should have been any trouble at all. Would any Christian now consent to give up the grand conceptions of Nature and of God thus opened to the human mind — the idea of infinite space full of worlds, of which our earth is one, moving in silent harmony as in a mystic dance ? Verily, this wolf has 23roved itself a harmless, nay, a very noble beast, and lies down in peace with the lambs. l^ext, it came in the shape of the law of gravitation, as sustentation of the cosmos by law and resident forces. The effect of this on religious thought was even more profound, though less visible on the surface, because only perceived by the most intelligent. It seemed at that time to remove God from the course of Nature. This was the real ground of the skepticism of the last century, and also the real motive of Voltaire's ardent advocacy of Newton's views before these were generally accepted in France. But now, who would give up this grand idea — this conception of law pervading infinite space — the same law which controls the falling of a stone guiding also the planetary orbs in their fiery courses ? This is indeed the divine spheral music, inaudible but to the ear of science, accompanying the celestial dance. Next, it came in the form of the antiquity of tlie earth and of the cosmos. The earth which we had fondly thouglit made specially for us about six thousand years ago ; sun, moon, and stars, which we had vainly imagined shone only for our behoof — these, science tells us, existed 2G4 eyolutio:n' and religious thought. and each performed its due course inconceivable ages before there was a man to till the ground or contemplate the heavens. Some of my readers may still remember the horror, the angry disjjute which followed the pro- mulgation of these facts. But now, who would consent to give up the noble conception of infinite time thus opened to the human mind and become forever the heri- tage of man ? Next, it came in the form of the antiquity of man. It is probable, na}^, certain, that man has inhabited the earth far longer than we had previously supposed we had warrant for believing. The controversy on this question and the dread of its result has indeed not yet entirely subsided. Some timid people still look askance at this wolf, but I think all intelligent people accept it and find it harmless. Next, and last, it comes now in the form of evolution — of the origin of all things, even of organic forms, by de- rivation — of creation hy law. AVe are even now in the midst of the terror created by this doctrine. But what is CA^olution but law throughout infinite time ? The _ same law which now controls the development of an egg .has presided over the creation of worlds. Infinite space and the universal law of gravitation ; infinite time and the universal law of CYolution. These two are the grandest ideas in the realm of thought. The one is universal sus- tcntation, the other universal creation, by law. There is one law and one energy pervading all space and stretch- ing through all time. Our religious philosophy has long INTRODUCTORY. 2G5 ago accepted the one, but has not yet had time to re- adjust itself completely to the other. A few more years, and Christians will not only accept, but love and cherish this also for the noble conceptions it gives of Nature and of God. But some will exclaim, '" Noble conceptions of God, say you I Why, it utterly obliterates the idea of God from the mind. All other conflicts were for outworks^ this strikes at the citadel. All others required only re- adjustment of claims, rectification of bounda^'ies betwixt science and religion — this requires nothing less than un- conditional surrender. Evolution is absolute material- asm, and materialism is incompatible with belief in Qod, and therefore with religion of any kind whatsoever ! " Before proceeding any further, it becomes necessary to remove this difficulty out of the way. CHAPTER II. THE EELATIOiT OF EYOLUTIOi^ TO MATERIALISM. It is seen in the sketch given in the previous chapter that, after eyery struggle between theology and science, there has been a readjustment of some beliefs, a giving up of some notions which really had nothing to do with religion in a proper sense, but which had become so associated with religious belief as be to confounded with the latter — a giving up of some line of defense which ought never to have been held because not within the rightful domain of theology at all. Until the present the whole difficulty has been the result of misconception, and Christianity has emerged from every struggle only strengthened and purified, by casting off an obstructing shell which hindered its growth. But the present strug- gle seems to many an entirely different and far more serious matter. To many it seems no longfer a struirsrle o CO of theology, but of essential religion itself — a deadly life-and-death struggle between religion and materialism. To many, both skeptics and Christians, evolution seems to be synonymous with blank materialism, and therefore cuts up by the roots every form of religion by denying RELATION OF EVOLUTION TO MxVTERIALISM. 267 the existence of GodanTthe fact of immortality. That. the enemies of religion, if there be any^such, should_ assume and insist on this identity, and thus carry over the whole accumulated eyidence of eyolutionliTaT dem~ onstration of materialism, although wholly unwarrant- ed, is not so surprising ; but what shall we say of the incredible folly of her friends in admitting the same identity ! A little reflection w411 explain this. There can be no doubt that there is at present a strong and to many an oyerwhelming tendency toward materialism. ,^The amaz- ing achieyements of modern science ; the absorj)tion of intellectual energy in the inyestigation of external nature and the laws of matter have created a current in that di- rection so strousf that of those Avho feel its influence — of those who do not stay at home, shut u]i in their creeds, but walk abroad in the light of modern thought— it sweeps away and bears on its bosom all but the strongest and most reflectiye minds. Materialism has thus become a fashion of thought; and, like all fashions, must be guarded against. This tendency has been created and is now guided by science. Just at this time it is strong- est in the department of biology, and especially is eyo- lution its stronghold. This theory is supposed by many to be simply demonstratiye of materialism. Once it was the theory of gravitation which seemed demonstratiye of materialism. The sustentation of the universe by law seemed to imply that Nature operates itself and needs no God. That time is passed. Now it is evolution and 268 EVOLUTION AND RELIGIOUS THOUGHT. creation by law. This will also pass. The theory seems to many the most materialistic of all scientific doctrine only because it is the last which is claimed by material- ism, and the absurdity of the claim is not yet made clear to many. The truth is, there is no such necessary connection between evolution and materialism as is imagined by some. There is no difference in this respect between evolution and any other law of Nature. In evolution, it is true, the last barrier is broken down, and the whole domam of nature is now subject to law ; but it is only the last ; the march of science has been in the same di- rection all the time. In a word, evolution is not only not identical with materialism, but, to the deep thinker, it has not added a feather's weight to its lorobability or reasonableness. Evolution is one thing and materialism quite another. The one is an established law of na- ture, the other an unwarranted and hasty inference from that law. Let no one imagine, as he is conducted by the materialistic scientist in the paths of evolution from the inorganic to the organic, from the organic to the animate, from the animate to the rational and moral, until he lands, as it seems to him, logically and inevita- bly, in universal materialism — let no such one imagine that he has walked all the way in the domain of science. He has stepped across the boundary into the domain of philosophy. But, on account of the strong tendency to materialism and the skillful guidance of his leaders, there seems to be no such boundary ; he does not dis- RELATION OF EVOLUTION TO MATERIALISM. 2G9 tino-uish between the inductions of science and tlie in- ferences of a shallow philosophy ; the w^hole is accredited to science, and the final conclusion seems to carry with it all the certainty wdiich belongs to scientific results. The fact that these materialistic conclusions are reached by some of the foremost scientists of the present day adds nothing to their probability. In a question of sci- ence, viz., the law of evolution, their authority is de- servedly high, but in a question of philosophy, viz., materialism, it is far otherwise. If the pure scientists smile when theological philosophers, unacquainted with the methods of science, undertake to dogmatize on the subject of evolution, they must pardon the philosophers if they also smile when the pure scientists imagine that they can at once solve questions in philosophy which have agitated the human mind from the earliest times. I am anxious to show the absurdity of this materialistic conclusion, but I shall try to do so, not by any labored argument, but by a few simple illustrations. 1. It is curious to observe how, when the question is concerning a work of Nature, we no sooner find out how a thino^ is made than w^e immediatelv exclaim : " It is not made at all, it became so of itself ! " So long as we knew not how worlds were made, we of course con- cluded they must have been created, but so soon as sci- ence showed Jioto it was probably done, immediately we say we wTre mistaken — they were not made at all. So also, so long as we could not imagine how new organic forms originated, we were willing to believe they were 270 EVOLUTIOX AND RELIGIOUS THOUGHT. created, but, so soon as we find that they originated by evolution, many at once say, ^^We were mistaken; no creator is necessary at all." Is this so when the question is concerning a work of man ? Yes, of one kind — viz., the work of the magician. Here, indeed, we believe in him, and are delighted with his work, until we know how it is done, and then all our faith and wonder cease. But in any honest work it is not so ; but, on the con- trary, when we understand how it is done, stupid wonder is changed into intellectual delight. Does it not seem, then, that to most peojole God is a mere wonder-worker, a chief magician. But the mission of science is to showjp us how things are done. Is it any wonder, then, that to such persons science is constantly destroying their super- stitious illusions ? But if God is an honest worker, ac- cording to reason — i. e., accordinsr to law — ouo-ht not science rather to change ga2:)ing wonder into intelligent delight — superstition into rational worship ? 2. Again, it is curious to observe how an old truth, if it come only in a neio form, often strikes us as some- thing unheard of, and even as paradoxical and almost impossible. A little over thirty years ago a little philo- sojihical toy, the gyroscope, was introduced and became very common. At first sight, it seems to violate all me- chanical laws, and set at naught the law of gravitation itself. A heavy brass wheel, four to five inches in diame- ter, at the end of a horizontal axle, six or eight inches long, is set rotating rapidly, and then the free end of the axis is supported by a string or otherwise. The wheel re- EELATIOX OF EVOLUTION TO MATERLVLISM. 071 mains suspended in the air while slowly gyrating. What mysterious force sustains the wiieel when its only point of support is at the end of the axle, six or eight inches away ? Scientific and popular literature were flooded with explanations of this seeming paradox. And yet it was nothing new. The boy's top, that spins and leans and will not fall, although solicited by gravity, so long as it spins, which we have seen all our lives without spe- cial wonder, is precisely the same thing. Now, evolution is no new thing, but an old familiar truth ; but, coming now in a new and questionable shape, lo, how it startles us out of our propriety ! Origin of forms by evolution is going on everywhere about us, both in the inorganic and the organic world. In its more fa- niiliar forms, it had never occurred to most of us that it was a scientific refutation of the existence of God, that it was a demonstration of materialism. But now it is pushed one step farther in the direction it has always been going — it is made to include also the origin of species — only a little change in its form, and lo, how we start ! To the deep thinker, now and always, there is and has been the alternative — materialism or theism. Go d oper ates Nature or Nature operates itself ; but evolution puts no new phase on this old question. For example, the origin of the individual by evolution. Everybody knows that every one of us individually became what we now are by a slow process of evolution from a microscopic spherule of protoplasm, and yet this did not interfere with the idea of God as our i ndividua l maker. Why, then, should 13 ~" """^ "^ 272 EVOLUTION" AND EELIGIOUS THOUGHT. the discovery that the species (or first individuals of each kind) originated by evolution destroy our belief in God as the creator of s^oecies ? 3. It is curious and very interesting to observe the manner in which vexed questions are always finally set- tled, if settled at all. All vexed questions — i. e., ques- tions which have tasked the powers of the greatest minds age after age — are such only because there is a real truth on both sides. Pure, unmixed error does not live to plague us long. Error, w^hen it continues to live, does so by virtue of a germ of truth contained. Great ques- tions, therefore, continue to be argued pro and con from age to age, because each side is in a sense — i. e., from its own point of view — true, but wrong in excluding the other point of view ; and a true solution, a true rational philosophy, will always be found in a view which com- bines and reconciles the two partial, mutually excluding views, showing in w^hat they are true and in what they are false — explaining their differences by transcending them. This is so universal and far-reaching a principle that I am sure I will be pardoned for illustrating it in the homeliest and tritest fashion. I will do so by means of the shield with the diverse sides, giving the story and construing it, however, in my own way. There is, apparently, no limit to. the amount of rich marrow of truth that may be extracted from these dry bones of popular proverbs and fables by patient turning and gnawing. We all remember, then, the famous dispute concern- RELATION OF EVOLUTION TO MATERIALISM. 273 ing the shield, with its sides of different colors, which we shall here call white and black. We all remember how, after vain attempts to discover the truth by dis- pute, it was agreed to try the scientific method of investi- gation. \Ye all remember the surprising result. Both parties to the dispute were right and both were wrong. Each was right from his point of view, but wrong in excluding the other point of view. Each was right in what he asserted, and each wrong in what he denied. And the complete truth was the combination of the partial truths and the elimination of the partial errors. But we must not make the mistake of supposing that truth consists in compromise. There is an old adage that truth lies in the middle between antagonistic ex- tremes. But it seems to us that this is the place of safety, not of truth. This is the favorite adage, there- fore, of the timid man, the time-server, the fence-man, not the truth-seeker. Suppose there had been on the occasion mentioned above one of these fence-philoso- phers. He would have said : '' These disputants are equally intelligent and equally valiant. One side says the shield is white, the other that it is black, now truth lies in the middle ; therefore, I conclude the shield is gray or neutral tint, or a sort of ]oepper-and-salt." Do we not see that he is the only man who has no truth in him ? No ; truth is no heterogeneous mixture of opjio- site extremes, but a stereoscopic combination of two sur-^ face views into one solid reality. Now, the same is true of all vexed questions, and I 274 EVOLUTION AND EELIGIOUS THOUGHT. have given this trite fable again only to apjjly it to the case in hand. There are three possible views concerning the origin of organic forms whether individual or S23ecific. Two of these are opposite and mutually excluding ; the third combining and reconciling. For example, take the in- dividual. There are three theories concerning the ori- gin of the individual. The first is that of the pious child who thinks that he was made verv much as he himself makes his dirt-nies : the second is that of the street-gamin, or of TojDsy, -who sa3^s : *^I was not made at all, I growed"; the third is that of most intelligent Christians— i. e., that we were made by a process of evo- lution. Observe that this latter combines and reconciles the other two, and is thus the more rational and philo- sophical. Now, there are also three exactly correspond- ing theories concerning the origin of species. The first is that of many pious persons and many intelligent clerg}'- men, who say that species were made at once by the Di- vine hand wifJiout natural ^^rocess. The second is that of the materialists, who say that species were not made at all, they were derived, ^^they growed.'' The third is that of the theistic evolutionists, who think that they were created by a process of evolution — who believe that mak- ing is not inconsistent with growing. The one asserts the divine agency, but denies natural process; the second asserts the natural process, but denies divine agency ; the third asserts divine agency hy natural process. Of the first two, observe, both are right and both wrong ; each RELATION OF EVOLUTION TO MATERIALISM. 275 view is right in what it asserts, and wrong in what it denies — each is right from its own point of view, but wrong in excluding the other point of view. The third is the only true rational solution, for it includes, com- bines, and reconciles the other two ; showing wherein each is right and wherein wrong. It is the combination of the two partial truths, and the elimination of the par- tial errors. But let us not fail to do perfect justice. The first two views of origin, whether of the individual or of the species, are indeed both partly wrong as well as partly right ; but the view of the pious child and of the Christian contains by far the more essential truth. Of the two sides of the shield, theirs is at least the whiter and more beautiful. But, alas ! the great bar to a speedy settlement of this question and the adoption of a rational philosophy is not in the head but in the heart — is not in the reason but in pride of opinion, self-conceit, dogmatism. The rarest of all gifts is a truly tolerant, rational spirit. In all our gettings let us strive to get this, for it alone is true wisdom. But we must not imagine that all the dogmatism is on one side, and that the theological. Many seem to think that theology has a ^'pre-emptive riglit^^ to dogmatism. If so, then modern materialistic science has ' 'jumped the claim.''' Dogmatism has its roots deep-bedded in the human heart. It showed itself first in the domain of theology, because there was the seat of power. In modern times it has gone over to the side of science, because here now is the place of power 276 EVOLUTION AND RELIGIOUS THOUGPIT. and fashion. There are tivo dogmatisms, both equally opposed to the true rational sj^irit, yiz., the old theologi- cal and the new scientific. The old clings fondly to old things, only because they are old ; the new grasps eagerly after new things, only because they are new. True wisdom and true philosophy, on the contrary, tries all things both old and new, and holds fast only to that wdiich is good and true. The new dogmatism taunts the old for credulity and superstition ; the old reproaches the new for levity and skepticism. But true wisdom perceives that they are both equally credulous and equal- ly skeptical. The old is credulous of old ideas and skeptical of new ; the new is skeptical of old ideas and credulous of new. Both deserve the unsj)aring rebuke of all right-minded men. The appropriate rebuke for the old dogmatism has been already put in the mouth of Job in the form of a bitter sneer : ^^Xo doubt ye are the people, and wisdom shall die with you.*' Tiie ap- propriate rebuke for the new dogmatism, though not put into the mouth of any ancient prophet, ought to be ut- tered — I will undertake to utter it here. I would say to these modern materialists, "No doubt 3^e are the men, and wisdom and true i^hilosophy were hor^i with you." Let it be observed that we are not here touching the general question of the personal agency of God in operat- ing JSTature. This we shall take up hereafter. All that we wish to insist on now is that the process and the law of evolution^does not differ in its relation to materialism from all other processes and laws of Nature. If the PvELATIOIT OF EVOLUTION TO MATERIALISM. 277 sustentation of the universe by the law of gravitation does not disturb our belief in God as the sustainer of the universe, there is no reason why the origin of the universe by the law of evolution should disturb our faith in God as the creator of the universe. If the law of gravitation be regarded as the Divine mode of susten- tation, there is no reason why we should not regard the law of evolution as the Divine process of creation. It is evident that if evolution be materialism, then is grav^-^ itation also materialism ; then is every law of Nature and all science materialism. If there be any difference at all, it consists only in this : that, as already said, here is the last line of defense of the supporters of supernatu- ralism in the realm of Nature. But being the last line of defense — the last ditch — it is evident that a yielding here implies not a mere shifting of line, but a change of base ; not a readjustment of details only, but a recon- struciio7i of Christian theology. This, I believe, is in- deed necessary. There can be little doubt in the mind of the thoughtful observer that we are even now on the eve of the greatest change in traditional views that has taken place since the birth of Christianity. But let no one be greatly disturbed thereby. For as then, so now, change comes not to destroy but to fulfill all our dearest hopes and aspirations ; as then, so now, the germ of living truth has, in the course of ages, become so en- crusted with meaningless traditions wliich stifle its growth, that it is necessary to break the shell to set it free ; as then, so now, it has become necessary to purge 278 EVOLUTION AND EELIGIOUS THOUGHT. religious belief of dross in the form of trivialities and superstitions. This has ever been and ever will be the function of science. The essentials of religious faith it does not, it can not, touch, but it purifies and ennobles our conceptions of Deity, and thus elevates the whole plane of religious thought. It will not, of course, be expected of me to give, even in briefest outline, a svstem of reconstructed Christian thought. Such an attempt would be wholly unbecoming. Time, very much time, and the co-operation of many minds, bringing contributions from many departments of thought, is necessary for this. In a word, it can only itself come by a gradual process of evolution. But from the point of view of science some very fundamental changes in traditional views are already plain. Of these the most fundamental and important are our ideas con- cerning God, Nature, and man in their relations to one another. These will form the subject of the next three cliapters. / OHAPTEr" III. / THE RELATIONS' OF GOD TO I^ATURE. rWE have already said that evolution does not differ essentially from other laws of ]N"ature in its hearing on ^ religious helief. It only reiterates and enforces with additional emphasis what Science, in all its departments, has heen saying all along. The difficulties in the way of certain traditional views have pressed with ever increas- ing force upon the thoughtful mind ever since the birth of modern science. All along, an issue has been gather- ing, but put off from time to time by compromise, until now, at last, the issue is forced upon us and compromise is exhausted. The issue (let us look it squarely in th e face) is : Either God is far more closely related with Na- ture, and operates it in a more direct way than we have recently been accustomed to think, or else (mark the al- ternative) Nature operates itself and needs no God at all. There is no middle ground tenable. Let us trace rapidly the growth of this issue. The old idea>and the most natural to the religious mind was the direct agency of God in every event and phenomenon of Nature. This view is nobly expressed in the noblest 280 EVOLUTION AND EELIGIOUS THOUGHT. literature in the world — in the Hebrew and Christian Scriptures : ^'He looketh on the earth and it trembleth. He toucheth the hills and they smoke." *'He maketh his sun to rise on the evil and on the good, and sendeth his rain on the just and on the unjust." But now comes Science and exj^lains all these phenomena by natural laws and resident forces, and we all accept her explanation. Thus, one by one the 2ihenomena of Xature are explained by the operation of resident forces according to natural laws, until the whole course of Kature, as we now know it, has been, or will be, or conceivably may be, thus ex- j)lained. Thus has gradually grown up, without our confessing it, a kind of scientific polytheism — one great Jehovah, perhaps, but with many agents or sub-gods, each inde- pendent, efficient, and doing all the real work in his own domain. The names of these, our gods, are gravity, light, heat, electricity, magnetism, chemical affinity, etc., and we are practically saying : " These be your gods, Israel, which brought you out of the land of Egyptian darkness and ignorance. These be the only gods ye need fear, and serve, and studv the wavs of." What, then, is practically the notion which most people seem to have of the relation of Deity to Nature ? It is that of a great master-mechanic far away above us and beyond our reach, who once upon a time, long ago, and once for all, worked, created matter, endowed it with necessary properties and powers, constructed at once out of hand this wonderful cosmos with its numberless THE RELATION OF GOD TO NATUPwE. 281 wheels within wheels, endowed it with forces, put springs in it, wound it up, set it a-going, and then — rested. The thing has continued to go of itself ever since. He might have n ot o nly rested but slept, and the thing: would have gone of itself. He might not only have slept but diecL { in(;| still the thin g would have continued to go o f itself. ^ But, no, I forget. He must not sleep or die, for the work is not absolutely perfect. There are some things too hard even for Him to do in this master- ful, god-like way. There are some things which even He can not do except in a 'prentice-like, man-like way. The hand must be introduced from time to time to repair, to rectify, to improve, especially to introduce new parts, such as new organic forms. Such was the state of the compromise until twenty- five years ago. J^ature is sufficient of itself for its course and continuance, but not for origins of at least some new parts. Such was the state of the compromise until Dar- win and the theory of evolution. But, now, even this poor privilege of occasional interference is taken away. Now, origins, as well as courses, are reduced to resident forces and natural law. Now, Nature is sufficient of it- ^ self, not only for sustentation, but also for creation. Thus, Science has seemed to push Him farther and far- / ther away from us, until now, at last, if this view be true, evolution finishes the matter by pushing Him en- tirely out of the universe and dispensing with Him alto- gether. Th2S,_of course, is materialism. But this is no new view now brought forward for the first time by evo- 282 EVOLUTION AND EELIGIOUS THOUGHT. lution. On the contrary, evolution only finishes what science has been doing* all along. See, then, how the issue is forced. Either Kature is sufficient of itself and wants no God at all, or else this whole idea, the history of which we have been tracing, is radically false. "We have here given by science either a demonstration of materialism or else a reductio ad ab- surdum. Which is it ? I do not hesitate a moment to say it is a reductio ad absurdum. And I believe that evolution has conferred an inestimable benefit on phi- losophy and on religion by forcing this issue and com- pelling us to take a more rational view. What, then, is the alternative view ? It is the utter rejection with Berkeley and with Swedenborg of the in- dependent existence of matter and the real efficient agency of natural forces. It is the frank return to the old idea of direct divine agency, but in a new, more ra- tional, less anthropomorphic form. It is the bringing together and complete reconciliation of the two appar- ently antagonistic and mutually excluding views of di- rect agency and naturcd laiv. Such reconciliation we have already seen is the true test of a rational philosophy. It is the belief in a God not far away beyond our reach, who once long ago enacted laws and created forces which continue of themselves to run the machine we call Na- ture, but a God immanent, a God resident m Nature, at all times and in all places directing every event and determining every phenomena — a God in whom in the most literal sense not only we but all things have their TOE RELATIO:^' OF GOD TO NATURE. 283 being, in whom all things consist, through whom all things exist, and without whom there would be and could be nothing. According to this view the phenomena of Nature are naught else than objectified modes of divine thought, the forces of Nature naught else than different forms of one omnipresent divine energy or will, the laws of Nature naught else than the regular modes of operation of that divine w^ill, invariable because He is unchangeable. According to this view the law of gravi- tation is naught else than the mode of operation of the divine energy in sustaining the cosmos — the divine meth- od of sustentation ; the law of evolution naught else than the mode of operation of the same divine energy in originating and developing the cosmos — the divine method of creation ; and Science is the systematic knowl- edge of these divine thoughts and ways — a rational sys- tem of natural theology. In a word, according to this view, there is no real efficient force but spirit, and no real independent existence but God. But some will object that this is pure Idealism. Yes, but far different from what usually goes under that name. The ideal philosophy as usually understood re- gards the external world as having no real objective ex- istence outside of ourselves — as objectified mental states of the observer — as literally such stuff as dreams are made of — as a mere phantasmagoria of trooping shadows bav- in sr no real existence but in the mind of the dreamer, and each dreamer makes his own world. Not so in the idealism above presented. According to tMs the exter- 284 EVOLUTION AND RELIGIOUS THOUGHT. nal world is the objectified niodeSj not of tlie mind of the observer, but of the mind of God. According to this, the external world is not a mere unsubstantial fig- ment or dream, but for us a very substantial objective reality surrounding us and conditioning us on every side. Again, it will be objected that this is pure Pantheism. Again, we answer ^'yes." Call it so if you like, but far different from what goes under that name, far different from the pantheism which sublimates the personality of the Deity into all-pervading unconscious force, and thereby dissipates all our hopes of personal relation with him. Properly understood, we believe this view com- pletely reconciles the two antagonistic and mutually ex- cluding views of impersonal pantheism and anthropomor- phic personalism, and is therefore more rational than either. The discussion of this most important point can only come up after the next chapter, because the argu- ment for the personality of Deity is derived, not from without by the study of Nature, but from within in our own consciousness. We therefore put off its discussion for the present. But, finally, some will object, *'We can not live and work effectively under such a theory unless, indeed, we escape through pantheism." It may, alas ! be true that this view brings us too near Him in our sense of spiritual nakedness and shortcoming. It may, indeed, be that we can not live and work in the continual realized presence of the Infinite. It may, indeed, be that we must still TUE RELATION OF GOD TO NATURE. 285 wear the veil of a practical materialism on our hearts and minds. It may, indeed, be that in our practical life and scientific work we must still continue to think of natural forces as efficient agents. But, if so, let us at least re- member that this attitude of mind must be regarded only as our ordinary work-clothes — necessary work-clothes it may be of our outer lower life — to be put aside when we return home to our inner higher life, religious and philo- sophical. CHAPTER IV. THE KELATIO^^ OF MAX TO MATURE. There are two widely distinct views concerning the relation of man to Nature ; the one as old as the history of human thought, the other only now urged upon us by modern science. According to the one, man is the counterpart and equivalent of Xature. He alone has — in fact is — an immortal spirit, and therefore he belongs to a world of his own. According to the other, man is but a part, a very insignificant part of Nature, and con- nected in the closest way with all other parts, especially with the animal kingdom. He has no world of his own, nor even kingdom of his own : he belongs to the animal kingdom. In that kingdom he has no deiiartment of his own : he is a vertebrate. In the department of verte- brates he has no privileged class of his own : he is a mammal. In the class of mammals he has no titled order of his own : he is a primate, and shares his pri- macy with apes. It is doubtful if he may enjoy the pri- vacy of a family of his own — the Hominidae — for the structural differences between man and the anthropoid apes are probably not so great as between the sheep family and the deer family. THE RELATION OF MAN TO NATURE. 2S7 i^ow it is evident that these two are only views from different points, psychical and structural. From the psychical point of view it is simply impossible to exag- gerate the wideness of the gap that separates man from even the highest animals. From this point of view man must be set over as an equivalent, not only to the whole animal kingdom, but to the whole of Nature be- sides. From the structural point of view, on the con- trary, it is impossible to exaggerate the closeness of the connection. Man's body is identified with all Nature in its chemical constituents, with the body of all animals in its functions, with all vertebrates, especially mammals, in its structure. Bone for bone, muscle for muscle, ganglion for ganglion, almost nerve-fiber for nerve-fiber, his body corresponds with that of the higher animals. Whether he was derived from lower animals or not, cer- tain it is that his structure even in the minutest details is precisely such as it would be if he were thus derived by successive slight modifications. Now, of these two views, the latter has been in recent times enormously productive in increasing our knowl- edge. Anatomy has become truly scientific only through comparative anatomy ; physiology through comparative physiology ; embryology through comparative embryol- ogy. Sociology is fast following in the same line, and becoming scientific through comparative sociology. Is not the same true also of psychology ? Will not psy- chology become truly scientific only through comparative psychology, i. e., by the study of the spirit of man in re- 288 EVOLUTION AND RELIGIOUS THOUGHT. lation to what corresponds to it in lower animals ? But this yiew and this method, when pushed to what seems to many their logical conclusion, end in identification of man with mere animals, of spirit with mere physical and chemical forces, immortality with mere conservation of energy, and thus leads to blank and universal materialism. Thus, while it increases our knowledge, it destroys our hopes. Is there any escape ? There is. The two extreme views given above are not irreconcilable. As already said, they are only views from different points, and there- fore, although both true, are equally one-sided and partial, and a true and rational philosophy, in this as in all other cases of vexed questions, is found only in a liigher view, which combines and reconciles these mutually excluding extremes. Can we find such a view ? I think we can. Let us first, however, trace some of the stages of this scientific materialism. There are two main branches of the argument for materialism : one derived from hrain-physiology, the other from evolution. As we wish to be perfectly fair, w^e will present and even joress the argument in both these directions, although the latter alone bears directly on the subject in hand. In recent times, physiology has made great and, to many, startling advances in the direction of connecting mental phenomena with brain-changes. Physiologists have established the correlation of vital with chemical and ph3^sical forces,* and probably in some sense, at * See an article by the author on this subject, " American Journal of THE RELATION OF MAN TO NATURE. least, of mental with yital forces. They have proVe^ia every act of perception, first a physical change in a nerve- terminal, then a propagated thrill along a nerve-fiber, and then a resulting change, physical or chemical, in the brain ; and in every act of volition, a change first in a brain-cell, then a return thrill along a nerve-fiber, and a resulting contraction of a muscle. Even the velocity of the transmission to and fro has been measured, and the time necessary to produce brain-changes estimated. They have also established the existence of physical and chemical changes in the brain corresponding to every change of mental state, and with great probability an exact quantitative relation between these changes of brain and the corresponding changes of mind. In the near future they may do more : they may localize all the different faculties and powers of the mind, each in its several place in the brain, and thus lay the foundations of a truly scientific phrenology. In the far-distant fu- ture we may possibly do much more. We may connect each kind of mental state wnth a different and distinctive kind of brain-change. We may find, for example, a right-handed rotation of atoms associated with love, and a left-handed rotation associated with hate, or a gentle sideways oscillation associated with consciousness, and a vertical pounding associated with ivill. Now, suj^pose all this, and even much more, be done in the way of associating, both in degree and in kind, mental changes Science," series ii, vol. xxviii, p. 305, 1859, and in ''Popular Science Monthly," vol. iv, p. 156, 1873. 290 EVOLUTION AND RELIGIOUS THOUGHT. with brain-clianges. What then ? '^ Why," say the ma- terialists, "we thereby identify mzVic? with matter, men- tal forces with material forces. Thought, emotion, con- sciousness and will become products of the brain, in the same sense as bile is a product of the liver, or urea a product of the kidneys." Such is, in brief, the argument. !N'ow, the answer : We may do all we have supposed and much more. AVe may push our knowledge in this direction as far as the boldest imagination can reach, and even then we are no nearer the solution of this mystery of the relation of brain-changes and mental changes than we are now. Even then it would be impossible for us to conceive how brain-changes produce mental changes or vice versa. Physical changes in sense-organs, transmitted along nerve-fibers, determine changes in brain-substance. So much is intelligible. But now there appear — how it is impossible to imagine — consciousness, thought, emotion, etc. — phenomena of an entirely different order, belong- ing to an entirely different world. So different, that it is impossible to imagine the nature of the nexus between, or to construe the one in terms of the other. Brain-cells are agitated and thought appears : Aladdin's lamp is rubbed, and the genie appears. There is just as much intelligible causal relation between the two sets of phe- nomena in the one case as in the other. Now, this mystery is not of the nature of those which disappear under the light of knowledge. On the con- trary, science only brings it out in sharper relief, and THE KELATION OF MAN TO NATUEE. 291 emphasizes its absolute unsolvableness. Suppose an ab- solutely perfect knowledge, i^erfect in degree, but human in kind. Suppose an ideally perfect science — a science which has so completely subdued its domain, and re- duced it to such perfect simplicity, that the whole cos- mos may be expressed in a single mathematical formula — a formula which, worked out with plus signs, would give every phenomenon and event which shall ever occur in the future, and with minus signs every phenomenon and event which has ever occurred in the past. Surely, this is an ideally perfect science. Yet, even to such a science, the relation of brain-changes to mental states would be as great a mystery as now. It would even come out in stronger relief, because so many other ap- parent mysteries would disappear. Like the essential nature of matter or the ultimate cause of force, this rela- tion lies evidently beyond the domain of science. It re- quires some other hind of knowledge than human to understand it. But materialists insist so much on the identity of brain-physiology with psychology, that even at the risk of tediousness we will multiply illustrations in order, if possible, to make this point still clearer. Suppose, then, we exposed the brain of a living man in a state of intense activity. Suppose, further, that our senses were abso- lutely perfect, so that we could see every change, of whatever sort, taking place in the brain-substance. What would we see ? Obviously nothing but molecular changes, physical and chemical ; for to the outside ob- 292 EVOLUTION AND EELIGIOUS THOUGHT. server there is absolutely nothing else there to see. But the subject sees nothing of all this. His experiences are of a different order, viz., consciousness, thought, emo- tions, etc. Viewed' from the outside, there is — there can be — nothing but motions ; viewed from the inside, noth- ing but thought, etc. — from the one side, only pliysical phenomena ; from the other side, only psychical phe- nomena. Is it not plain that, from the very nature of the case, it must ever be so ? Certain vibrations of brain molecules, certain oxidations with the formation of car- bonic acid, water, and urea on the one side, and there appear on the other sensations, consciousness, thoughts, desires, volitions. There are, as it w^re, two sheets of blotting-paj^er jDasted together. The one is the brain, the other the mind. Certain ink-scratches or blotches, utterly meaningless on the one, soak through and appear on the other as intelUgihle writing, but how we know not, and can never hope to guess. But wdien the paste dissolves, shall the writing remain^ We shall see. But some will object. There is nothing specially strange and unique in all this, for the same mystery un- derlies the essential nature of all kinds of force and matter, and therefore all phenomena. True enough, but with this difference. Physical and chemical forces and phenomena are indeed incomprehensible in their es- sential nature ; but once accept their existence, and all their different forms are mutuallv convertible, construa- ble In terms of each other and all in terms of motion. But it is impossible by any stretch of the imagination THE RELATION OF MAN TO NATURE. 293 to thus construe mental forces and mental phenomena. It may, indeed, be impossible to conceive lioio came the plane of material existence, but, standing on that plane, all phenomena fall into intelligible order. But there is another plane above this one, having no intelligible relation with it. We must climb up and stand on this before its phenomena fall into intelligible order. In a word, material forces and phenomena are, indeed, a mystery, but only of the p^st order. But mental and moral forces and phenomena are a mystery even from the standpoint of the other, and are therefore a mystery of the second order — a mystery withm a mystery. We repeat, then, with additional emphasis after this examination, that we can not imagine between physical and psychical phenomena a relation of cause and effect in the same sense in which we use these terms in physi- cal science, although in some sense there is doubtless such a relation. If man were the only animal we had to deal with, there would be no standing ground left for materialism. But there is still another difficultv which sticks deeper. It is that suggested by the laio of evolu- tion and enforced by the comparative method. Relation of Man to Animals. — Man, we say, is en- dowed with, is, in fact, an immortal spirit. What is spirit ? We know things only by their phenomena ; what are the phenomena of spirit ? Consciousness, will, intelligence, memory, love, liate, fear, desire — surely these are some of them. But has not a dog or a monkey all these ? Pressed with this difficulty, some have in- 294 EVOLUTIOI^ AND KELIGIOUS THOUGHT. deed felt compelled to accord immortal spirit to higher animals. But we can not stop here. If to these, then also to all animals ; for we haye here only a sliding scale without break. Can we stop now and make it coexten- sive Avith sentiency ? No ; for the lowest animals and lowest plants merge into each other so completely that no one can draw the line between them with certainty. We must extend it to plants also. Shall we stop here and make immortal spirit coextensive with life ? We can not ; for life-force is certainly correlated with, trans- mutable into, and derivable from, physical and chemical forces. AVe must extend it into dead nature also. Therefore, everything is immortal or none. Our boasted immortality resolves itself into indestructibility of mat- ter and force, but not of form, nor of consciousness and lyersonality. Such an immortality is of no value to us. Thus, then, if once we pass the gap between man and the higher animals, there is no possibility of a stopping- place anywhere. Such is the difficulty presented by comparison in the taxonomic series. Take now the embryonic series. Each one of us, individually, was formed gradually by a pro- cess of evolution, from a microscopic spherule of proto- plasm undistinguishable in structure from the lowest forms of protozoal life. Now, in this gradual process of evolution, where did immortal spirit come in ? Was it in the germ-cell ? Then why deny it to the i:>rotozoan ? Was it at the quickening, or at the birth, or at the mo- ment of first self -consciousness, or at some later period of THE EELATION" OF MAN TO NATURE. 295 capacity of abstract thought ? Again, when it did come in, was it something superadded or did it grow out of something ah-eady existing in the embryo or the infant ? Or take the evolution series from protozoan to man. This we have ah'eady seen is similar in outline to the other two. JS'ow, in the gradual evolution of the animal kingdom throughout all geological time, terminating in man, when did immortal spirit come in ? Did it enter with life, or with sentient life, or somewhere in the ascending scale of animals, or with the advent of man ? If with man, was it some new thing added at once out of hand, or did it grow out of something already exist- ing in animals ? This last, we are persuaded, is the only tenable view — the only view that can effect that reconciliation between the two extreme, mutually excluding views now usually held, which, as already seen, is the true test of a rational philosophy. I believe that the spirit of man luas devel- oped out of the anima or conscious principle of animals, and that this, again, was developed out of the lower forms of life-force, and this in its turn out of the chemical and physical forces of Nature ; and that at a certain stage in this gradual development, viz., with man, it acquired i\\Q property of immortality precisely as it now^, in the indi- vidual history of each man at a certain stage, acquires the capacity of abstract thought. This is, in brief, the view which I wish to enforce. The reader must under- stand, however, that this is my oiun vieio only, a view for which I have earnestly contended for twenty years. It 14 296 EVOLUTION AND RELIGIOUS THOUGHT. appeals, therefore, not to authority, but only to reason. I wish now to present it as briefly as possible. First, then, I would draw attention to the fact that there is nothing wholly exceptional in such transforma- tion with the sudden appearance of new powers and properties ; but, on the contrary, it is in accordance with many analogies in the lower forces, and therefore a priori not only credible but probable. For example, force and matter may be said to exist noiv on several distinct planes raised one above another. There is a sort of taxonomic scale of force and matter. These are, 1, the plane of elements ; 2, the plane of chemical com- pounds ; 3, the plane of vegetal life ; 4, the plane of animal life ; and 5, the plane of rational and, as we hope, immortal life. Each plane has its own appropriate force and distinctive phenomena. On the first operates physi- cal forces, producing physical phenomena only — for the oi^eration of chemical affinity immediately raises mat- ter to the next plane. On the second plane operates, in addition to physical, also chemical forces, producing all those changes by action and reaction, the study of which constitutes the science of chemistry. On the third plane, in addition to the two preceding forces, with their char- acteristic iihenomena, operates also life-force, produc- ing the distinctive phenomena characteristic of living things. On the fourth plane, in addition to all lower forces and their phenomena, operates also a higher form of life-force characteristic of animals, producing the phe- nomena characteristic of sentient life, such as sensation. THE RELATION OF MAN TO NATURE. 297 consciousness, and will. On the fifth plane, in addition to all the preceding forces and phenomena, we have also the forces and phenomena characteristic of rational and moral life. Now, although there are doubtless great differences of level on each of these planes, yet there is a very distinct break between each. Although there are various degrees of the force characteristic of each, yet the difference be- tween the characteristic forces is one of kind as well as of degree. Although energy by transmutation may take all these different forms, and thus does now circulate up and down through all these planes, yet the passage from one plane upward to another is not a gradual passage by slid- ing scale, but at one hound. When the necessary condi- tions are present, a new and higher form of force at once appears, Wke a Mrtli into a higher sphere. For example, when hydrogen and oxygen are brought together under proper conditions, water is born — a new thing with new and wiiolly unexpected properties and powers, entirely different from those of its components. When C0„, H^O, and NH3 are brought together under suitable conditions, viz., in the green leaves of plants, in the presence of sun- light, living protoplasm is then and there born, a some- thing having entirely new and unexpected powers and properties. It is no gradual process but sudden, like birth into a higher sphere. Now, there is not the least doubt that the same is true of the order and manner of the first appearance of the natural forces in the phylogenic series. In the history of 298 EVOLUTION AND RELIGIOUS THOUGHT. the evolution of the cosmos, the forces of Nature have appeared successively and suddenly when conditions be- came favorable. There was a time in the history of the earth w^hen only physical forces existed, chemical affinity being held in abeyance by the intensity of the heat.* By gradual cooling, chemical affinity at a certain stage came into being — was born, a new form of force, with new and peculiar phenomena, though doubtless derived from the preceding. Ages upon ages passed away until the time was ripe and conditions were favorable, and life appeared — a new and higher form of force, jDroducing a still more peculiar group of phenomena, but still, as I believe, de- rived from the preceding. Ages upon ages again passed away, during wdiich this life-force took on higher and higher forms — in the highest foreshadowing and simu- latinsf reason itself — until finallv, when the time was fully ripe and conditions were exceptionally favorable, spirit, self-conscious, self-determining, rational, and moral, appeared — a new and still higher form of force, but still, as I am persuaded, derived from the preceding. But some will ask, " How is this consistent with im- mortality ? " In answer, let me again remind the reader that with every new form of force, with every new birth of the universal energy into a higher plane, there appear new, unexpected, and, previous to experience, wholly un- imaginable properties and powers. This last birth is of course no exception. Why may not immortality be one * All chemical compounds are dissociated by sufficient heat. THE RELATION OF MAN TO NATURE. 299 of these new properties ? But this j)oint is so important that we must treat it more fully. Eemember, then, the view of the relation of God to Nature, already ex|)lained. Eemember that the forces of Nature are naught else than different forms of the one omnipresent Divine energy. Remember that, as just shown, this Divine omnipresent energy has taken on suc- cessively higher and higher forms in the course of cosmic time. Now this upward movement has been wholly by increasing individtuctlon, not only of matter, but also of force. This universal Divine energy, in a genei*alized condition, tmincUviduated, diffused, pervading all Na- ture, is what we call physical and chemical force. The same energy in higher form, individuating matter, and itself individuated, but only yet very imperfectly, is what we call the life-force * of plants. The same energy, more fully individuating matter and itself more fully in- dividuated, but not completely, we call the anima of * I knorr it is the fashion to ridicule the use of the terms vitality, vital force, as a remnant of an old superstition ; and yet the same men who do so use the terms gravity, electricity, chemical force, etc. Vital force is indeed correlated with other forces of Nature, but is none the less a distinct form of force, far more distinct than any other unless it be the still higher form of psychical, and therefore it better deserves a distinct name than any lower form. Each form of force gives rise to a peculiar group of phenomena, and the study of these to a special depart- ment of science. Xow, the group of phenomena called vital is more peculiar, more different from other groups than these are from each other, and the science of physiology is a more distinct department than either physics or chemistry, and therefore the form of force, which de- termines these phenomena, is more distinct and better entitled to a name than any physical or chemical force. 300 EVOLUTION AND RELIGIOUS THOUGHT. animals. This anima, or auimal soul, as time went on, was individuated more and more until it resembled and foreshadovv'ed the spirit of man. Finally, still the same energy, completely individuated as a separate entity, and therefore self-conscious ; capable of separate existence, and therefore immortal, we call the spirit of man. According to this view, the vital principle of plants and the anima of animals are but different stages of the development of spirit in the womb of Xature : in man at last it came to hirth. In plants and animals it was in deep embryo sleep — in the latter, quickened, indeed, but not viable — still unconscious of self, incapable of inde- pendent life, with physical, umbilical connection with Mature ; but now at last in man, separated from Xature, capable of independent life, born into a new and higher l">lane of existence. Separated, but not wholly ; Xature is no longer gestative mother, but still nursing mother of spirit. As the organic embryo at birth reaches inde- pendent material or temporal life, even so spirit embryo by birth attains independent sjoiritual or eternal life. Although birth is its truest correspondence and best illustration, yet we may vary the illustration in many ways. In animals spirit is deep submerged in Nature as beneath a water-surface, wholly unknowing of any higher, freer world above. In man sj)irit emerges above the sur- face into a higher world, looks down on Nature beneath him, around on other emerged spirits about him, and up- ward to the Father of all spirits above him. Emerged but not wholly free — head above, but not yet foot-loose. THE RELATION OF MAN TO NATCRE. 301 Or, again : As a planet must break away from physi- cal, cohesive connection with the central sun (planet- birth) in order to enter into higher gravitative relations, which thenceforward determine all its movements in beautiful harmony ; as the embryo must break away from physical umbilical connection with the mother in order to enter into higher spiritual bonds of love, which thenceforward determine all their mutual rela- tions — even so s])iYit must break away from physical and material connection with the forces of Nature, which are but the omnipresent Divine energy, in order there- by to enter into higher relations of filial love to God and brotherly love to man. Finally, as the new-born child differs little in grade of physical organization from the mature but unborn embryo, but at the moment of birth there is a sudden and complete change, not so much in the grade of organization but in the whole plane of existence — a change absolutely necessary for farther advance, for another cycle of life ; even so at the moment of the origin of man, howsoever this may have been accomplished, there may have been no great change in the grade of psycJiical structure, but yet a complete change in the /:>/«?ie of psychical life — a change absolutely necessary for further advance, for another cycle of evolution. In both cases there is a sudden entrance into a new world, the sudden appearance of a new creature with entirely different capacities — a pass- ing out of an old world, a waking up in a new and higher. According to this view, man alone is a child of 302 EVOLUTION AND RELIGIOUS THOUGHT. God, callable of separate spirit-life — separate but not yet wholly independent of Nature. As already said. Nature is no longer gestative mother, but still nursing mother of spirit — we are weaned only by death. Or, again : As in passing up the organic scale, we find all grades of completeness of organic individuality, an increasing individuation of bodily form, which com- pletes itself as a perfect organic individual only in the higher animals, so, also, in passing up the dy7icunic scale, force or energy is individuated more and more until the process reaches completeness as a spirit individual or dynamic individual — a person only in man. The more we reflect on this subject, the more we shall be convinced that completed spirit-individuality explains, as nothing else can, all that is characteristic of man. It is this which constitutes person, or the self-acting ego. It is this which constitutes self-con- sciousness, free-will, and moral responsibility. And out of these again grow the recognition of relations to other moral beings and to God, and therefore ethics and religion. Out of these, also, grow the capacity of indefi- nite voluntary progi'ess. This also means separate life, spirit-viability, or immortality. Self-consciousness espe- cially seems to me the simplest sign of separate entity or spirit-individuality, and its appearance among psychical phenomena the very act of spirit-Mrtli. We may imag- ine man to have emerged ever so gradually from ani- mals : in this gradual develoj^ment the moment he be- came conscious of self, the moment he turned his THE KELATION OF MAN TO NATURE. 303 thoughts inward in wonder upon himself and on the mystery of his existence as separate from Xature, that moment marks the birth of humanity out of animality. All else characteristic of man followed as a necessary consequence. I am quite sure that, if any animal, say a dog or a monkey, could be educated up to the point of self-consciousness (which, however, I am sure is imjios- sible), that moment he (no longer it) would become a moral responsible being, and all else characteristic of moral beings would follow. At that moment would come personality, immortality, capacity of voluntary progress ; and science, philosoph}^, religion would quick- ly follow. We have emphasized self-consciousness as the most fundamental sign of spirit-individuality ; but a difference of exactly the same kind is found running through the whole gamut of human faculties as compared with corre- sponding faculties in animals. As animal consciousness is related to human self-consciousness, so exactly is ani- mal will to human free will, animal intelligence to hu- man reason, animal sign-language to rational grammati- cal speech of man, constructive art of animals to true ra- tional progressive art of man. In every one of these the resemblance is great, but the difference is immense, and not only in degree, but also in kind. In every case it is like shadow and substance, projnise and fulfillment, or, still better, it is like embryo and child. The change from one to the other is like to a birth into a higher sphere, the beginning of another cycle of evolution. We 304 EVOLUTION AND RELIGIOUS THOUGHT. would like to follow this idea out in detail, but it would lead us beyond the scope of this work. Those who desire to do so we would refer to an article bv the author on the *^^ Psychical Eelation of Man to Animals." * Some General Conclusions. — There are, however, two or three thoughts so closely connected with what we have already said that we can not pass -them over. 1. We have seen that every mental state corresponds with a particular brain state, and every mental change with a brain change. We have, therefore, here, two series, physical and psychical, corresponding with each other, term for term. For everv chano;e in the one there is a corresponding change in the other, both in kind and amount. Now, is not this the test of the relation of cause and effect ? It certainly is. Yes, there must be a causal relation here, even though we are not able to understand the nature of the causal nexus. But which is cause and which effect ? If the view above presented be correct, then in animals hrain changes are in all cases the cause of psychical phenomena. In man alone, and only in his higher activities, psychic changes precede and determine brain changes. In man alone brain changes are determined not only by external but by internal im^xQ&^ioi^^. Man alone perceives not only oh- JQcts—riiaferial things — but also relations and properties abstracted from the objects, i. e., ideal things; and, moreover, not only relations between objects, but also * "Princeton Review" for May, 1884. THE KELATION OF MAN TO NATURE. 305 relations between relations or ideas. In man alone there is an inner world — microcosm — the things of which are thoughts, ideas, etc. This self-acting poiuer of spirit on the things of itself, instead of merely re- acting as played upon by external nature, is charac- teristic of man, and is a necessary result and a sign of seyerance, partial at least, of physical bond with Nature. 2. Again, I have used the term vital principle. I must justify it. I know full well that it is the fashion to ridicule the term as a remnant of an old superstition which regards vital force as a sort of supernatural entity unrelated to other forces of Nature. No one has striven more earnestly than myself to establish the correlation of vital with physical and chemical forces ; and yet, if the view above presented be true, there is a Jciiid of justifica- tion even for the term vital principle — much more, vital force. There is a kind of reason and true insight in the personification of the forces of Nature, and especially of vital force. All forces, by progressive dynamic indi- viduation, are on the way toward entity, but fully attains that condition only in man. 3. Again, to perceive relations and properties ab- scracted from material things, to form abstract or general ideas, to form not only percepts but also cojicejtts, is ad- mitted to be a characteristic of man — a characteristic on which all our science and philosophy rest. From time immemorial the vexed question has been debated, " Have such abstract or general ideas any real existence, or are 806 EVOLUTION AND RELIGIOUS THOUGHT. they mere names of figments of the mind?" This is the famous question of realism and nominalism. Now, if our view be correct, then there is one most funda- mental abstraction, viz., self, which is indeed a realiti). Self-consciousness is the direct recognition of the one reality, spirit, of which all others are the sign and shadow — the true reality which underlies and gives po- tency to all abstractions or ideas. Do we not find in this view, then, the foundation of a true realism, or rather a complete reconciliation of realism and nominalism ? 4. Thus, then, Nature, through the whole geological history of the earth, was gestative mother of spirit, which, after its long embryonic development, came to birth and independent life and immortality in man. Is there any conceivable meaning in Nature without this consummation ? All CA'olution has its beginning, its course, its end. Without spirit-immortality this beauti- ful cosmos, which has been developing into increasing beauty for so many millions of years, when its evolution has run its course and all is over, would be precisely as if it had never been — an idle dream, an idiot tale signifying nothing. I repeat : Without spirit-immortality the cos- mos has no meaning. Now mark : It is equally evident that, ivitliout this gestative method of creation of spirit, the whole geological history of the earth previous to man would have no meaning. If man's spirit were made at once out of hand, why all this elaborate preparation by evolution of the orsranic kin2:dom ? Thus, again, man is born of Nature into a higher na- THE RELATION OF MAN TO NATURE. 307 ture. He therefore alone is possessed of two natures — a lower, in common with animals, and a higher, peculiar to himself. The whole mission and life-work of man is the progressive and finally the complete dominance, both in the individual and in the race, of the higher over the lower. The whole meaning of sin is the humiliating bondage of the higher to the lower. As the material evolution of Nature found its goal, its completion, and its significance in man, so must man enter immediately upon a higher sinritual evolution to find its goal and completion and its significance in the ideal man — the Divine man. As spirit, unconscious in the w^omb of Na- ture, continued to develop by necessarij law until it came to birth and independent life in man, so the new-born spirit of man, both in the individual and in the race, must ever strive by freer law to attain, through a newer birth, unto a higher life. CHAPTER V. THE RELATIOJi OF GOD TO MAX. In" the two preceding chapters we have discussed the relation of God to Nature and of man to Nature. There is still another relation, if possible, of still more vital im- portance to us, viz., the relation of God to man. This, of course, introduces the question of revelation — a sub- ject which I approach with some reluctance. I feel I am treading on holj ground, and must do so with shoes re- moved. If it be asked, How is evolution concerned with the subject of revelation ? I answer Evolution emphasizes and enforces the reign of law taught by all science, and makes it at last universal. Manv conclude, therefore, that, if evolution be true, a belief in the possi- bility of any form of revelation is irrational. I do not think this follows, and I will give my reasons. I do so, however, very briefly, because we are not yet ready to formulate our views except in the most general way. If man be indeed something more than a higher spe- cies of animal ; if man's spii'it be indeed a spark of Di- vine energy individuated to the point of self-conscious- ness and recognition of his relation to God ; if spirit- THE RELATION OF GOD TO MAN. 309 embryo, developing in the womb of Nature through all geological time, came to birth and independent spirit-life in man, and thus man alone is a child of God as well as a product of Nature — if all this be true, then it is evident that this wholly neiu relation requires also a wholly differ- ent mode of Divine operation. If God operates on Nature only by regular j)rocesses, Avhich we call statural laius, then he 7mist operate on spirit in a different and a more direct way, and this we call revelation. If to the student of Nature it is inconceivable that He should operate on Nature except by natural law^s (for this is the name we give to His chosen mode of operation there), then to the student of theology it is equally incon- ceivable, if our view of man be true, that He should not operate on spirit in some more direct and higher way, i. e., by revelation. But some will ask, Is not this a palpable violation of law ? I think not. All divine operations are, must be, according to reason, i. e., according to law. The opera- tion of the divine on the human spirit, i. e., revelation, must therefore be according to law, but a higher law than that which governs Nature, and, therefore, from the point of view of Xature, supernatural. There is nothing wholly unique in this. Life is a higher form of force than the physical and chemical. Life-phenomena are therefore super-physical, and if we confined the term Nature to dead Nature they would be supernatural. So the free, self-determined acts of spirit on spirit, even of the spirit of man on the spirit of man, much more of the 310 EVOLUTION AXD RELIGIOUS THOUGHT. Spirit of God on the spirit of man, may be according to law, and yet from the natural point of view be super- natural. It is true that, in the complex of phenomena, material and spiritual inextricably woven together, which go to make up human life, Science must ever strive to reduce as much as possible to material laws, for this is her domain, and she is bound to extend it ; but, if our view of man be true, there will always remain a large residuum of phenomena — a whole world of phe- nomena — which will never yield, because clearly beyond her domain. Standing on the lower material plane, these phenomena are wholly super-material, and therefore in- comprehensible from the material point of view. We must rise and stand on the higher plane before these also are reduced to law, but a higher law than that operating on the lower plane. If, therefore, science insists on ban- ishing the supernatural from the realm of Xature, the- ology may reasonably insist on its necessity, in this sense, in the realm of morals and relidon. If, then, the direct influence of the Sjoirit of God on the spirit of man be what we call revelation, then there is evidently no other kind of revelation jDossible ; and, furthermore, such revelation is given to all men in different degrees. It is given to all men as conscience ; in greater measure to all great and good men as clearer perception of righteousness ; in pre-eminent measure to Hebrew prophets and Christian apostles ; but supremely and perfectly to Jesus alone. But there is, and in the nature of things there can be, no test of truth but rea- THE KELATION^ OF GOD TO MAX. 311 son. "We must fearlessly, but honestly and reverently, try all things, even revelations, by this test. We must not regard, as so many do, the spirit of man as the pass- ive amanuensis of the Spirit of God. Eevelations to man mast of necessity partake of the imperfections of the medium through which it comes. As pure water from heaven, falling upon and filtering through earth, must gather impurities in its course differing in amount and kind according to the earth, even so the pure divine truth, filtering through man's mind, must take imperfec- tions characteristic of the man and of the age. Such fil- trate must be redistilled in the alembic of reason to separate the divine truth from the earthy impurities. CHAPTER VI. THE objectio:n", that the above view implies pan- theism, ANSWERED. It will be observed that the views presented in the last three chapters are closely connected with one another, and all conditioned on the *^ Relation of God to Nature," urged in Chapter III. Now it will doubtless be objected to this view, especially as applied in Chajoter IV on the ^' Relation of Man to Nature," that it js naught else than pure pantheism ; that it destroys completely the personal- ity of Deity, and with it all our hopes of communion with him, and all our aspirations of love and worship toward him ; that, according to this "view, God becomes only the soul or animating principle of Nature, operat- ing everywhere but unconsciously like the yital principle of an organism ; that the whole cosmos becomes in fact a great organism, developing under the o^ieration of resi- dent force according to necessary law, only that ivc apotheosize this omnipresent force and call it God ; and finally, that God is naught else than an abstraction, created like other abstractions or general ideas wholly by the human mind, and having no objective existence. OBJECTIOiT ANSWERED. 313 Furthermore, it will be said, that according to this view, this omni2:)resent unconscious energy individuates itself by necessary law of evolution more and more until it reaches, for the Ji7'st time tn man, self-consciousness and immortality, and thus that man himself is the only self- conscious immortal being in existence, and therefore the only being worthy of reverence and worship. Thus, this view leads to humanity-worship or rather to self-ivorhM]). I feel the full force of this objection. I answer it as follows : I freely admit that, following up this scientific line of thought alone, we are carried strongly in the direc- tion of pantheism. But there is nothing strange or ex- ceptional in this. In all the deepest questions, single lines of thought inevitably carry us to extreme one-sided views. This seems to be the necessary result of the essentially two-fold nature of man, self-conscious spirit in a material body, the relation between which is, and must ever be, irtscrutable. On this account there is and must be a fundamental antithesis in human philosophy, i.e., two lines of thought, the material and spiritual, which lead to two apparently irreconcilable views.* We have already seen that a rational philosophy, whenever we are able to reach such, is always found in a higher and more comprehensive view, which includes, combines, and rec- onciles two one-sided, partial, and mutually excluding views. But spirit and matter, or mind and brain, or God * For a fuller statement of this antithesis, see an article by the author entitled " Evolution in Relation to Materialism," " Princeton Review," for March, 1881. 314 EVOLUTION AND EELIGIOUS THOUGHT. and Nature, is the fundamental antithesis which underlies and is the cause of all other lesser antitheses. This anti- thesis, therefore, is absolutely fundamental, and therefore forever irreconcilable. We must accept both sides, even though we can not clearly perceive the nature of their relation. AYe must be content with comj^romise where we can not effect complete reconciliation. We must frankly acknowledge that the antagonism is apparent only, and the result of the limitation of our faculties, and believe that, if we could only rise to a high enough point of view, like all other antitheses, this also would disappear in a rational philosophy. Now, to apply these principles. No one, we admit, can form a clear conception of how immanence of Deity is consistent with personality, and yet we must accept both, because we are irresistibly led to each of these by different lines of thought. Science, following one line of thought, uncorrected by a wider philosophy, is naturally led toward one extreme — i^antheistic immanence ; the devout worshiper, following the wants of his religious nature, is naturally led toward another extreme of anthro- pomorphic personality. The only rational view is to accept both immanence and personality, even though we can not clearly reconcile them, i. e., immanence without pantheism, and personality without anthropomorphism. AVe have already seen in the third chapter, how follow- ing the scientific line of thought, we are logically driven to immanence. We wish now to show how, following an- other line of thought, we are as logically driven to per- OBJECTIOX ANSWERED. 315 Gonality. On this most difficult subject, howevGr, all we are prepared to do is to throw out some brief suggestions, in the hope that they may be carried out more perfectly by some thoughtful reader ; scatter some seed- thoughts, in the hope that, falling haply on good soil, they may spring up and bear more fruit than I have been able to produce. 1. In the gradual individuation of the universal Di- vine energy described in Chapter IV, there must of course be a corresponding growth of a kind of independent self- activity which reaches completeness in man, and in fact constitutes what we call self-consciousness and free will. The exact nature of the relation of Deity or of the gen- eral forces of Nature to this gradually individuated por- tion, I do not undertake to define. And how this idea of partial self-activity comports with the absoluteness of Deity we can not clearly understand. But this fact need not specially disturb us here ; for this is only one branch of the wider question of the moral agency of man in rela- tion to the absolute sovereignty of God, or the freedom of man in relation to necessary law in J^ature. 2. We have already shown that, if the brain of a living, thinking man were exposed to the scrutiny of an out- side observer with absolutely perfect senses, all that he would or could possibly see would, be molecular motions, physical and chemical. But the subject himself, the thinking, self-conscious spirit, would experience and ob- serve by introspection only consciousness, thought, emo- tion, etc. On the outside, only physical phenomena ; on the inside only psychical phenomena. Now, must 316 EVOLUTION AND RELIGIOUS THOUGHT. not the same he necessarily true of Nature also ? Viewed from the outside by the scientific observer, nothing is seen, nothing can be seen, there is nothing else to be seen, but motions, material phenomena ; but behind these, on the other side, on the inside, must not there be in this case also psychical i:)henomena, conscious- ness, thought, will; in a word, personality?* In the only place w4iere we do get behind physical phenomena, viz., in the brain, w^e find psychical phenomena. Are we not justified, then, in concluding that in all cases the psychical hes behind the physical ? The human brain is a wonderful instrument, by means of which, in some inscrutable way, viz., in our own experience, we do get behind, on the other side, on the inside of some mate- rial phenomena, and in so far become partakers of the Divine nature. But behind other phenomena of Nature we may never hope to penetrate either by observation or experience, but only in dim way by highest reason. Sci- ence, even in the case of the brain, can not pass from the one kind of phenomena to the other. If she would study the inside she must abandon the outside — she must aban- don the microscope and take to introspection. If she would study the phenomena of the higher platform, she must leave the low^r and climb up and stand on the hisfher. If this be true of the brain where the two kinds of phenomena are brought so close together, how much more is it true of the phenomena of the cosmos. AVe * Johnstone, " Stoncy-Nature," vol. xxxi, p. 422. OBJECTION ANSWERED. 317 can never hope, either by observation or by experience, to pass beyond the veil. We must abandon the methods of science and reach it, if at all, in some other way. Not the clear-sighted but the pure-hearted shall see God. In the light of what is said above, it is almost amus- ing to see how persistently some writers try to expel mind from Nature, while others as anxiously strive to retain for mind at least some small corner, especially as one of the causes or factors of evolution.* Both sides wholly misconceive the matter, although the former are more consistent. One of the causes ! Mind is either all or none ; so also mechanics is all or none. It is all mind through mechanics. It is all mechanics from the outside, and it is all mind from the inside. For science it is all me- chanics, for theology it is all mind. It is the duty of philosophy to reconcile these two opposite views. In one form of evolution only, viz., in human progress, is mind one of the factors of evolution. But to think and speak thus of God in relation to Nature is to place him on the human plane. Thus, then, we see that our own self-conscious person- ality behind brain phenomena compels us to accept con- sciousness, will, thought, personality behind Nature. Now I assert that once get this abstract idea in the mind, and by a necessary law of thought it gradually expands without limit, and eventuallv reaches the form of infinite consciousness, will, thought, etc., and therefore of an in- * See " Nature," vol. xxxiv, pp. 355 and 385, 18S6. 318 EVOLUTION AND RELIGIOUS THOUGHT. finite person. This law of indefinite expansion may be illustrated by the ideas of space and time. The animal, and indeed the infant, understands space and time only in their relation to itself, but has not yet abstracted these from their contents. This comes only with the birth of self-conscious personality. But, so soon as the abstract idea of space is acquired, by a necessary law of mental activity it expands without limit, and finally becomes the idea of infinite space. Similarly, so soon as the idea of time as abstracted from its contents is conceived, it inevitably expands without limit and grows into the idea of infinite time. So is it precisely with the idea of self-conscious personality. The animal or the very young child is indeed conscioas of its body and of external objects in their mutual relations, but not of self, as ab- stracted from its contents. The animal never attains it, the child does, l^ow, so soon as this idea of self-con- scious personality — of a spiritual entity underlying mate- rial phenomena — appears, by a necessary law of mental activity it expands without limit, and inevitably reaches the idea of an infinite self, an infinite person, God, be- hind the phenomena of Nature. But some will object that this idea of infinite person- ality is inconceivable. True enough, but the opposite is far more inconceivaUe. The ideas of infinite space and infinite time are also inconceivable, yet we must accept them, because the idea of all space or all time being lim- ited is still more inconceivable ; for if we think of space or time as limited, immediately there comes the ques- OBJECTIOiT ANSWERED. 319 tion, 'MVliat is there beyond the limit?" There is therefore this wide difference between these two in- conceivables : the one is so only in the sense of tran- scending the power of our mind, but the other is un- thinkable, self-colitradictory, absurd. So also is it with self-conscious personality. The idea of an infinite self, i. e., God, is indeed inconceivable, but only in the sense of transcending our power of comprehension ; but the idea of the consciousness behind the cosmos as being limited or finite is more than inconceivable, it is unthinkable, self-contradictory, absurd ; for immediately comes the question, '^ What is there beyond which limits it ?" To the Greek mind Zeus was limited, therefore of necessity came also the idea of Fate, superior to and limiting Zeus himself. To them, therefore. Fate was the real God — the absolute. 3. We have thus far spoken only or principally of self-consciousness, but the same precisely is true of an- other essential attribute of personality, viz., free will. Every one admits causative force or forces operating in Nature. Science has shown that all the different kinds of force are but different forms of one omnipresent energy. Now, looking abroad on Nature from the out- side, this omnipresent energy seems to modern science as simply resident, inherent in matter itself, and therefore as operating unconsciously and by necessity. But the question occurs, " Whence did we get the idea of force, energy, causation V I answer unhesitatingly : We get it not from without by observation of Nature, but from 15 320 EVOLUTION AND RELIGIOUS THOUGHT. within through consciousness ; not from the outside view, but from, the inside yiew of phenomena. We can not conceive of phenomena without force, of effects without cause, because we are intensely conscious of being our- selves through our wills an active cause of external phe- nomena. If we were merely passive observers, not ac- tive causers of changes in the external world, tlien these external phenomena would seem to us merely to shift and change and succeed each in a certain order. AVe misfht note the order and determine the laws of se- quence, and thus form a science ; but it would never enter into our minds to imagine any causal or dynamical nexus between them. In the mind of such passive ob- server, but not doer — thinker, but not worker — would be completely realized the only thorough-going and con- sistent materialistic philosophy, i. c., a philosophy in which, like Comte's, cause and force have no place — are in fact banished as a superstition from science. But the clear consciousness of essential energy, of causative force within, the certainty that we ourselves, through our wills and by the conscious exertion of force do de- termine changes in the external world, compels us to attribute all changes to causative force of some kind, and naturally enough, until the interference of science, to a personal will like our own. Thus by a necessary law we project our internal states into external Nature. But see now the steps of evolution of this idea. At first, i. e., in the uncultured races, and also in childhood, external forces take the form of a personal will like our OBJECTIOE" ANSWERED. 321 own residing in each object, and controlling its phenom- ena as our wills control our bodily movements (fetich- ism). Then, as culture advances, it takes next the form of several personal wills controlling each the phenom- ena of a different department of Nature (polytheism). Finally, in the highest stage of culture, it takes the form of one personal will controlling the phenomena of the whole cosmos (monotheism). To the religious but unscientific mind in all these stages the personal will is anthropomorjbhic. But we have already seen (Chapter III) how anthropomorphism has been driven by science from one department after another, until now at last by evolution it is driven out of Nature entirely, and to those following this line of thought alone, the phe- nomena of Nature are relegated to forces inherent in matter, and operating by laws necessary and fatal ; and not only so, but material forces are made to invade even the realm of consciousness, and reduce this also to material laws. Thus the savage ejects his own conscious personal will into every separate object of Nature ; the modern materialist ejects material forces into the realm of consciousness.. But, as already seen, a rational phi- losophy admits these two antithetic views, and strives to combine and reconcile them. This reconciliation, as far as it is possible for us, is found in a personal will im- manent in Nature, and determining directly all its phenomena. Thus it is evident that the idea of a causal nexus between successive phenomena is a primary conception, 322 EVOLUTION AND PwELIGIOUS THOUGHT. and therefore ineradicable and certain. Even from the purest evolution point of view it must be true, for, if man's mind grew out of the forces of Nature, this idea must represent a fact in Xature. Also, analysis shows that all causative force originates in luill. Lastly, cul- ture and reason, by a necessary law of expansion, car- ry us uj^ward to the conception of one infinite sus- taining and creative will. Science may sometimes ob- scure but can not destroy this idea. Evolution, which was supposed by some to have destroyed it for ever, has only temporarily obscured it in the minds of the unre- flecting, by the supposed identity of evolution with materialism. From this tem2:)orary eclipse it now emerges with still greater clearness and far greater no- bleness. For, observe : All the effects known to us in Nature are finite ; therefore a personal will, which deter- mines these separately by successive acts, as we do, must also be finite like ourselves. But a will, which bv one eternal act ever-doing, never done, determines the evolu- tion and the sustentation of an infinite cosmos, must it- self be infinite. Thus onlv in the doctrine of universal evolution do we rise to a just conception of God as an in- finite cause. 4. As the idea of cause and force is related to loill, so precisely is the idea of design related to tliouglit. We get this also, not from without, but from within. Adap- tation of means to ends is in our experience the result of thought, and we can not conceive it to result otherwise. The effect of science can not be to destroy this primary OBJECTION ANSWERED. 323 conception — wliicli, indeed, like all primary conceptions, is ineradicable, and already more certain than anything can be made by proof — but only to exalt and purify our conceptions of the Designer. For, observe : In any case of adaptive structure, whether in the animal body or in planetary relations, the evidence of design is not in the materials, but in the use of the materials ; not in the parts, but in the adjustment of the parts for a purpose. Design, purpose, adjustment, adaptation, are not ma- terial things, but relations or intellectual things, and therefore perceivable only by thought, and conceivable only as the result of thought. It is simply impossible to talk about such adaptive structures without using lan- guage which implies design. The very word ^^ adaptive " implies it. It is impossible even to think of such struct- ures without implicitly assuming intelligence as the cause. It makes no particle of difference lioio the mate- rial originated, or whether it ever originated at all ; it matters not whether the adaptation was done at once out of hand, or whether by slow process of modification ; it matters not whether the adaptive modification was brought about by a process of natural selection, or by pressure of a physical environment ; whether without law or according to law. The removal of the result from man- like directness of separate action can not destroy the idea of design, but only modify our conception of the Designer. What science, and especially evolution, destroys, there- fore, is not the idea of design, but only our low anthropo- morphic notions of the mode of working of the Designer. 324 EYOLUTION AND RELIGIOUS THOUGHT. Precisely the same change takes place here under the influence of science as has taken place in all our notions concerning God. The uncultured savage sees a separate god in every object. As culture advances, his gods be- come fewer and nobler, until, in the most advanced states, man recognizes but one infinite God, the creator and sustainer of all. God is still in every phenomenon, but no longer as a separate God, but only as the sepa- rate manifestation of the One. Thus culture takes away our gods, but only to compel us to seek him in nobler forms until we reach the only true God. But, even after the conception of the one God is reached, how many seem to regard him as altogether such a one as our- selves ; but science shows us that his ways are not like our ways, nor his ends as our ends. Thus science, more than all other kinds of culture, simplifies while it infinitely ennobles and purifies our conceptions of Deity. Again, the same change takes place in our sense of mystery. I suppose most people imagine that it is the special mission of science to destroy all mystery. Many seem to think that superstition, or even religion, is in- separably connected with ignorance and mystery, and all must disappear together before the light of science. But not so. There is only a gradual progressive change — an evolution in the form of myster}^ as well as in the form of religion. To the savage everything is a sepa- rate mystery. The function of science is, indeed, to destroy tliese separate mysteries, by explaining them ; but, in doing so, it only reduces them to fewer and OBJECTION ANSWERED. 325 grander mysteries, and these again to still fewer and grander, until, in an ideally perfect science, all separate and partial mysteries are swallowed up in the one all- embracing infinite mystery — the mystery of existence. There is still mystery in each object, but no longer a separate mystery — only a separate manifestation of the one overwhelming mystery. Or, again, and finally : The same change occurs in our ideas of creation. At first every object is a separate creation — a manufacture. With advancing science these separate, creative acts become fewer and nobler, until now, at last, in evolution, all are embraced and swallowed up in one eternal act of creation — a never-ceasing pro- cession of the divine energy. Every object is still a creation, but not a separate creation — only a separate manifestation of the one continuous creative act. Now, precisely the same change must take i^lace in onr conception of design in Nature. To the uncultured there is a distinct and separate design in every separate w^ork of Nature. But, as science advances, all these distinct, separate, petty, man-like designs are merged into fewer and grander designs, until, finally, in evolu- tion at last, we reach the conception of the one infinite, all-embracing design, stretching across infinite space, and continuing unchanged through infinite time, wiiich in- cludes and predetermines and absorbs every possible separate design. There is still design in everything, but no longer a separate design — only a separate manifesta- tion of the one infinite design. 326 EVOLUTION AND RELIGIOUS THOUGHT. Thus, then, our own self-consciousness and will and thought give rise, necessarily, to the conception of an infinite self-consciousness, will, and thought — i. e., God. The necessity to believe in self-conscious spirit behind bodily phenomena compels us to believe also in an infi- nite self-conscious spirit behind cosmic phenomena. Looking at the operations of this ever-active spirit, wheth- er in the one case or the other, from the outside, it looks like unconscious energy inherent in matter itself, and therefore like necessity, or fate. But, looked at from the inside in the one case, we perceive only self-conscious, free activity of spirit. Therefore, we are compelled to acknowledge in the other case, also, the same source of all activity, the same cause of all phenomena. We are compelled to acknowledge an infinite immanent Deity behind phenomena, but manifested to us on the outside as an all-pervasive energy. But some portion of this all- pervasive energy again individuates itself more and more, and therefore acquires more and more a kind of independent self-activity which reaches its completeness in man as self-consciousness and free will. We said, '^ a Z;i;i<:/ 0/ independent self-activity." How this comports with the absoluteness of God we can not understand, any more than we can understand how it comports with invariable law in Nature. We simply accept them both as primary truths, even though we can never hope to rec- oncile them completely, because we can not understand the exact nature of the relation of spirit to matter. We can not look at the outside and the inside at the same objectio:n" answered. 327 time. If we could understand the relation of psychical phenomena to brain-changes, then might we hope to understand far more perfectly than now the relation of God to Nature. But as in the one case, the brain, al- though we can not understand the nature of the relation, yet we are sure of the intimacy of the connection of the two series, psychical and physical, term for term ; so in the other case, the cosmos, although we can not under- stand the exact nature, we are sure of the intimacy of the connection, term for term — every material phenomenon and event with a corresponding psychical phenomenon as its cause. CHAPTER VII. THE RELATION OF EVOLUTIOi^ TO THE PROfeLEM OF ETIL. The problem of evil has tasked the power and baffled the skill of the greatest thinkers in every age. It would be folly in me to imagine that I can solve it. Its com- plete solution is probably impossible in the jiresent state of science. Yet I can not doubt that on this, as on every important question relating to man, the theory of evolu- tion will throw new and important light. All I can hope to do is to throw out some brief suggestions on the sub- ject. If evolution be true, and especially if man be indeed a product of evolution, then what w'e call evil is not a unique phenomenon confined to man, and the result of an accident, but must be a great fact pervading all na- ture, and a part of its very constitution. It must have existed in all time in different forms, and subject like all else to the law of evolution. Let us, then, trace rap- idly some of the steps of this evolution. 1. External Physical Evil in the Animal Kingdom. — As already seen in previous chapters, the necessary condition of evolution of the organic kingdom is a strug- EVOLUTION AND THE PROBLEM OF EVIL. 329 gle for life — a conflict on every side, with a seemingly inimical environment and a survival of only the strong- est, the swiftest, or the most cunning — in a word, the fittest. Now, suppose the course of organic evolution finished in the introduction of man, and from this vant- age-ground we look back over the course and consider its result. Shall we call that evil which was the neces- sary condition of the progressive elevation which cul- minated so gloriously ? Evil doubtless it seemed to the individual, struggling animal, but is this worthy to be weighed in comparison with the evolution of the whole organic kingdom until it culminated in man ? Is it not rather a good in disguise ? I suppose human arrogance may be willing enough to admit it in this case, where animals only are sufferers. 2. Physical Evil in Relation to Man. — But organic evolution, completed in man, was immediately trans- ferred to a higher plane, and continued as social evolu- tion ; material evolution is transformed into psychical evolution ; unconscious evolution, according to neces- sary law, to conscious voluntary progress toward a rec- ognized goal, and according to 2^ freer law. But in this transformation the fundamental conditions of evolution do not change. Man also is surrounded on every side with what at first seems to him an evil environment, against which he must ever struggle or perish. Heat and cold, tempest and flood, volcanoes and earthquakes, savage beasts and still more savage men. What is the remedy — the only conceivable remedy ? Knowledge of 330 EVOLUTION AND RELIGIOUS THOUGHT. the laws of Nature, and tliereby acquisition of power over Nature. But increasing knowledge and power are equivalent to progressive elevation in the scale of psychi- cal being. This conflict witli what seems an evil en- vironment is, therefore, the necessary condition of such elevation. It is not too much to say that, without this condition, except for this necessity for struggle, man could never have emerged out of animality into human- ity, or, having thus emerged, would never have risen above the lowest possible stage. Now sujopose, again, this ideal to have been attained — suppose knowledge of physical laws and power over physical forces to be com- plete — suppose physical nature completely subdued, put beneath our feet, and subject to our will, and, from the high intellectual position thus attained, we look back over the wiiole ground and consider the result. Shall that be called evil which was obviously the necessary condition for attaining our then elevated position ? Evil it doubtless seemed to the individuals who fell, and still seems to us who now suffer, by the way in the conflict ; but is physical discomfort or even physical death of the individual to be weighed in comparison with the ps3Thical elevation of the individual, and espe- cially of the race ? Evidently, then, physical evil even in the case of man is only seeming evil, but real good. 3. Organic Evil — Disease. — But there is a more dreadful form of evil than that which results from ex- ternal physical nature — an evil far more subtle and diffi- cult to understand, and therefore to conquer. I mean EVOLUTION AND TPIE PROBLEM OF EVIL. 331 internal organic evil — disease in its diversified forms and with its attendant weakness and suffering, inscrutable often in its causes, insidious in its approaches, conta- gious, infectious, spreading from house to house, carry- ing suffering and death in its course, and leaving sorrow and desolation behind. Is there any remedy which can transmute this evil into good ? There is. It is again knowledge—knowledge of the laws, and power over the forces, of organic nature. Is it not evident that complete knowledge of the laws of health and the causes of dis- ease would put this evil also under our feet ? Is it not evident that a perfect knowledge of the laws of health, and a perfect living according to these laws, would so entirely subdue this evil that men would no longer die except by natural decay or by accident ? Is it not evi- dent, also, that the race will not attain this knowledge unless it be forced upon us by the necessity of avoiding the dread evil of disease ? Now suppose, again, this ideal attained, suppose this dread evil subdued by complete knowledge, and again from our elevated intellectual position we look back over the ground. Shall we call that evil which was the ne- cessary condition of our intellectual elevation ? Evil, doubtless, it seems to us individuals who have suffered and are still suffering through our ignorance ; but is such individual suffering or even individual death to be weighed against the psychical elevation of the in- dividual and evolution of the race ? Ought not the individual to be willins: to suffer thus much vicarious- 332 EVOLUTION AND RELIGIOUS THOUGHT. oo^ ly for the race ? Is not this seeming evil also a real good ? May we not, then, confldently generalize ? May we not say that all physical evil is good in its general effect — that every law of Nature is beneficent in its general operation, and, if sometimes evil in its specific operation, is so only through our ignorance ? Partly by survival of the fittest, and partly by intelligence, man, like other animals, brings himself in accord with the laws of K'a- ture, and thus appropriates the good and avoids the evil, and Nature becomes beneficent only. But, also unlike any other animal, man by rational knowledge makes the laws of Nature his servants, and uses them for his own l^urposes, thus increasing his power and elevating the plane of his life. 4. Moral Evil. — But there is still another form of evil, the most dreadful of all. This one may be called the evil, in some sense, tlie only evil. It is that of which all other forms are but the shadows cast backward and downward along the course of evolution and on lower stages of existence. This consummation of all evil is sin — moral disease — more dreadfully contagious and deadly than any organic disease. What shall we say now ? Is there any rational explanation of this evil ? Is there any possible reason or excuse for an all-wise, all- powerful Ruler afflicting man alone of all His creatures with this greatest of all evils ? In all other cases, the individual and the ra€e sacrifice themselves for a time physically for the sake of final spiritual elevation ; but EVOLUTION AND THE PROBLEM OF EVIL. 333 this is spiiHtual debasement. In all other cases, there is a sacrifice in the course in order to attain the goal, but this is a missing of the goal itself. Is there any view which mitigates this evil, any philosophic alchemy which can transmute this evil into good ? Age after age the human mind has prostrated itself in helpless paralysis before this problem. Most thinkers have been content to say, *'Thou hast ordered it so. Thou art good. It must be right." Bat many, and among them some of the best minds, have said, '' Either God is not all-good, or else not all-wise, or else not all-powerful, or else there is no God at all." Does evolution shed any light on this dread problem ? I believe it docs. We have said that all other evils are but shadows of this one, cast backward and downward on earlier stages of CYolution and lower forms of existence. But from the evolution point of view these earlier and lower forms of evil are rather to be regarded as /oreshado wings of the reality to come. They are but earlier and lower stages of the evolution of the same tiling— emhrjonic condi- tions of the now full-grown evil. If so, then the same law must apply here also, though, as we shall see, with a difference. Here, also, the individual as well as tlie race finds himself surrounded by what seems an evil en- vironment, against which he must struggle. The spirit of man is inclosed and conditioned by a lower environ- ment, which he must subdue or perish. Here, then, is again a deadly conflict : ^'a law in the members warring against the law of the siw.rit, and bringing it into captiv- 534 EVOLUTION AND KELIGIOUS THOUGnT. ity " ; a law of selfism warring against the law of love, and bringing it into subjection ; solicitations to debasement on the one hand, and solicitations to wrong others on the other. How shall it be overcome ? What is the reme- dy ? Again I answer, Knowledge of and conformity to the laivs of the moral tuorlcl. But, as in other cases, so in this : this knowledge of and conformity to law, wdiich is the true goal of humanity, will not be attained unless it is forced upon us by necessity and in self-defense — i. e., by evil. Now supi^ose, once more, this knowledge and con- formity be complete, and the ideal of humanity be at- tained, and from this final and highest position we look back over the whole ground. Shall that be called evil which from the very nature of a moral being and the laws of evolution was obviously the necessary condition of attaining the goal ? Shall we not from this final posi- tion call it a good in disguise ? Evil, doubtless, it seems to us who suffer and stumble and mayhap fall by the way ; but shall the mishap of the individual be weighed as an equivalent against the evolution of the race and the attainment of its goal ? Ah ! there is the rub. It is- all well enough to talk of sacrificing the physical individual to the race, but not so the spiritual. If we believe in the immortality of the human spirit, if we do indeed stand related to God in the manner explained in Chapter IV, then moral evil in the individual has an entirely peculiar and an eternal significance — then the individual human spirit EVOLUTION AND THE PROBLEM OF EVIL. 335 has an infinite worth and can not be sacrificed to the race ; for tiie evohition of the race itself is only in order to the perfecting of individual human souls. What shall we say now ? I answer : The sacrifice is not ne- cessary. There is in the realm of morals alone a way of escape — a saving element which redeems the individual without violating the law. Let me explain. It will, I think, be admitted by all that innocence and virtue are two very different things. Innocence is a pre-estahlislied, virtue a self -established, harmony of spiritual activities. The course of human development, whether individual or racial, is from innocence through more or less discord and conflict to virtue. And virtue completed, regarded as a condition, is holiness, as an activity, is spiritual freedom. Not happiness nor inno- cence but virtue is the goal of humanity. Happiness will surely come in the train of virtue, but if we seek primarily happiness we miss both. Two things must be borne steadily in mind : virtue is the goal of humanity ; virtue can not be given, it must be self-acquired. Xow we have already seen that in all evil the remedy, which not only cures it but transmutes it into good, is knowledge of law and conformity of conduct thereto — a true science and a successful art — in a word, knowledge of the laws of God and obedience to these laws. In the physical world ignorance of these laws is necessarily fatal, but not so in the moral world. Ignorance here is not necessarily fatal though dangerous. By the very nature of a moral being, the essential thing is not knowledge but 336 EVOLUTION AND RELIGIOUS THOUGHT. character or virtue — the loill to know and the effort to obe}^ In the ph3^sical realm, knowledge is the goal ; in the moral realm, knowledge is only in order to virtue. Therefore, in the case of the individual struggling with moral evil within and without, the victory is always in his power. If he fails, it is his own fault. His utmost ef- fort in this field must be successful, because the result is not external, but internal and in the realm of moral freedom. The spirit of man is self-acting and in some sense, though not absolutely, self-existing, and can not be ruined except by its own act. In the moral world, where the goal is not knowledge but character, attainment must be in proportion to honest endeavor in the right spirit. Evil, then, has its roots in the necessary law of evo- lution. It is a necessary condition of all progress, and pre-eminently so of moral j^rogress. But some will ask, *' Why could not man have been made a perfectly pure, innocent, happy being, unplagued by evil and incapable of sin ? " I answer : The thing is impossible even to omnipotence, because it is a contradiction in terms. Such a being would also be incapable of virtue, would not be a moral being at all, would not in fact be man. We can not even conceive of a moral being without free- dom to choose. We can not even conceive of virtue without successful conflict with solicitations to de- basement. But these solicitations are so strong and so often overcome us, that we are prone to regard the solici- tations themselves as essential evil instead of our weak surrender to them. EVOLUTION AND THE PROBLEM OF EVIL. 337 All evolution, all j^rogress, is from lower to higher plarie. From a philosophic point of view, things are not good and evil, but only higher and lower. All things are good in their true places, each under each, and all must work together for the good of the ideal man. Each lower forms the basis and underlying condition of the higher ; each higher must subordinate the lower to its own higher uses, or else it fails of its true end. The physical world forms the basis and condition of the or- ganic, yet the organism rises to a higher plane only by ceaseless conflict with and adaptation to the physical en- vironment, which therefore seems in some sense evil. The organic world in its turn underlies and conditions and flourishes the rational moral world. As the senses are the necessary feeders of the intellect, so the appe- tites are the necessary feeders of the moral nature. Yes, even the lowest sensual appetites are the necessary basis and nourishers of our highest moral sentiments. And yet the struggle for mastery of the higher spiritual with the lovver animal is often so severe that the latter seems to many as essential evil to be extirpated, instead of a useful servant to be controlled. This view is asceti- cism. Now the whole view of evil usually held is a kind of asceticism, and therefore, like asceticism, must be only a transition phase of human thought. All that we call evil both in the material and the spiritual world is good, so long as we hold it in subjection as servants to the spirit, and only becomes evil when we succumb. All evil con- sists in the dominance of the lower over the higher; all 338 EV0LUTI05T AND KELIGIOUS THOUGHT. goodwill the rational use of the lower by the higher. True virtue consists, not in the extirpation of the lower, but in its subjection to the higher. The stronger the lower is, the better, if only it be held in subjection. For the hiojher is nourished and strenc^thened bv its connec- tion with the more robust lower, and the lower is puri- fied, refined, and glorified by its connection with tlie diviner higher, and by this mutual action the whole plane of being is elevated. It is only by action and re- action of all parts of our complex nature that true virtue is attained. INDEX Acceleration, law of, 160. African fauna explained, 186. Agassiz, his greatest result, 29, 43 ; relation to evolution, 32, 3Y, 43 ; relation to Darwin, 46 ; compared with Kepler, 47. Ages of geological history, 1 6. Alpine species explained, 197. Amphibians, development of, 1S2. Analogy and homology, 81. Anima of animals, 295, 299. Animal architecture, styles of, 91. Animal kingdom, primary divisions of, 89. Animals, relation of man to, 293 ; spirit embryonic in, 293. Antiquity of man, religion and, 264 ; of the earth, religion and, 263. Aortic arches, proofs of evolution from, 133. Arthropods, 114. Artificial production of varieties, 204. Australia, fauna and flora of, ex- plained, 182; when isolated, 184. Barriers limit faunal and floral re- gions, 170. Beauty, origin of, 251. Birds' tails, changes of, 156. Brain,vertebrate, proofs of evolution from, 144 ; vertebrate, changes of, in phylogenic series, 150; relation to mind, 304, 315. Brain-physiology as a basis for ma- terialism, 288. Branching tree illustrates evolu- tion, 13-15, 18, 92, 232. Brooks, W. K., on the cause of va- riations, 244. Californian coast-islands, fauna and flora of, 193. Causation, idea of, from within, 319. Centers of creation, specific, 176. Cephalization, 153. Chambers, his views on evolution, 34. Changes slow at present, 248. Close-breeding, effects of, 218, 225. Coast-islands of California, fauna and flora of, 193. Comparison, method of, 41. Conflict between religion and sci- ence, 262. Continental faunas and floras, 170. 340 INDEX. Continental island life, 190. Continuity, law of, 53 ; law of, ap- plied to inorganic forms, 54 ; to organic forms, 56, Cope's law of acceleration, 160. Creation, special, 30, 69; specific centers of, 176; changes in our notions of, 325. Cross-breeding, law of, 218. Cross-fertility of artificial varieties, 214. Cross-sterility, 77, 216. Cyclical movement, law of, 16, 22. Darwin, relation to Agassiz, 46 ; compared with Newton, 48 ; fac- tors of evolution discovered by, V4; objections to his theory of evolution, 76. Derivation, origin of inorganic forms by, 54 ; origin of organic forms by, 56. Design, idea of, from within, 322 ; argument from, not destroyed by evolution, 323 ; changes in our ideas of, 325. Differentiation, law of, 11, 19; law of, in embryonic development, 19; law of, illustrated, 126; of the animal kingdom illustrated, 158. Disease, necessity of, 330. Divine energy, forms of, 299. Divisions of the animal kingdom, 89. Dogmatism, theological and scien- tific, 275. Domestication, changes produced by, 204. Egg, development of, 3, 19. Egyptian species unchanged in three thousand years, 247. Embryology, proofs of evolution from, 130. Environment, physical, 73. Evil, problem of, relation of evolu- tion to, 328 ; physical, necessity of, 329 ; a condition of progress 329, 336; organic, necessity of, 330 ; moral, necessity of, 332. Evolution, what is, 3, 8 ; scope of, 3 ; type of, 3, 8 ; examples of, 5 ; popularly limited to the organic kingdom, 7; progressive change in, 9 ; laws of, 11; illustrated by branching tree, 13-15, IS, 92, 232 ; misconception of, 14 ; pro- duced by resident forces, 27 ; germs of the idea, 32 ; relation of Agassiz to, 32, 37, 43 ; Lamarck's views on, 33 ; Chambers's views on, 34 ; obstacle to, removed, 35 ; confliction with relidon imar^i- nary, 45 ; how related to gravita- tion, 49 ; general evidences of, 53; artificial, 60; observed, 62; certainty of, 65; special proofs of, 67 ; factors of, 73 ; proofs of, from the vertebrate skeleton, 93 ; from the articulate skeleton, 114 ; from embryology, 130 ; from de- velopment of amphibians, 132; from aortic arches, 133; from vertebrate brain, 144 ; from rudi- raentary organs, 161 ; from geo- graphical distribution of organ- isms, 165; explains geographical diversity, 177; objection to this view, 199; answer, 201; proofs of, from artificial modifications, 204 ; factors of, operative in do- mestication, 210 ; paroxysmal, INDEX. 341 239; material, nearly completed, 249 ; thoroudily established, 257 ; relation to religion, 258, 264 ; re- lation to materialism, 266; ne- cessitates great change in relig- ious thought, 2Y7 ; of forces, 297 ; relation to revelation, 308 ; pantheistic objection answered, 312 ; relation to problem of evil, 828. Experimental method largely fails on plane of life, 40. Factors of evolution, 73. Faculties, evolution of, 23. Faunas and floras, geographical, 165 ; continental, 170 ; marine, 174 ; special cases of distinct, 174; of Australia, 182; of Afri- ca, 186; of Madagascar, 187; of continental islands, 190; of the coast-islands of California, 1 93 ; of oceanic islands, 195; of lofty mountains, 197. Fish-tails, changes of, in develop- ment, 154 ; in evolution, 153. Fishes, age of, 17. Floras and faunas, geographic il, 165. Force, vital, correlation of, 36 ; planes of, 296 ; evolution of, 297 ; idea of, from within, 319. Forces, resident, evolution by, 27 ; of Nature are forms of Divine energy, 299. Fore-limbs, vertebrate, homologies of, 95. Generation, spontaneous, 15. Geographical faunas and floras, 165 ; diversity, theory of, 175 ; diver- sity explained by evolution, 177 ; objection to this view, 199; an- swer, 201 ; present diversity de- termined by Glacial epoch, 180. Geological record, imperfection of, 234. Glacial epoch determined distribu- tion of species, 177, 180, 197; changes during, in America, 180 ; in Europe, 181. God, relation of, to Nature, 279 ; im- manence of, in Nature, 282 ; rela- tion of, to man, 308 ; personality of, 314 ; necessary belief in, 326. Good and the true, relation of, 259. Grasshopper, external anatomy of, 125. Gravitation, relation of, to evolu- tion, 49 ; and religion, 263. Gyroscope, 270. Heliocentric theory and religion, 262. Hind-limbs, vertebrate, homologies of, 103. Horse, genesis of, 108. Homologies of vertebrate skeleton, 93 ; of vertebrate fore-limbs, 95 ; of vertebrate hind-limbs, 103 ; of articulate skeleton, 114. Homology and analogy, 81 ; only within primary divisions, 90. Hyatt, A., on Planorbis, 236. Idealism, true and false, 283. Immortality in accord with law, 298. Individuality, organic, 302 ; spirit- ual, 302. Innocence and virtue compared, 342 INDEX. Inorganic forms, law of continuity applied to, 54. Intermediate forms between arti- ficial varieties, 214. Islands, continental and oceanic 189. Kepler compared with Agassiz, 47. Lamarck, evolutionary views of, 33 74. Law of differentiation, 11, 19 ; of progress of the whole, 13, 22 ; of cyclical movement, 16, 22; of continuity, o3 ; of continuity ap- plied to inorganic forms, 54 ; to organic forms, 56 ; of differenti- ation illustrated, 126 ; of acceler- ation, 160 ; of cross-breeding, 218. Laws of evolution, 11, 19. Lepidosiren, 83. Life, nature of, 35 ; imperfectly subject to experiment, 40; rela- tion of, to philosophy, 259. Limbs, vei'tebrate, homology of, 95. Links, connecting, 12, 57, 127; con- necting, elimination of, 230 ; con- necting, usually absent from geo- logical faunas, 233. Liquidambar, 200, 202. Lobster, external anatomy of, 118. Lungs, formation of, 82. MadagasCan fauna explained, 187. Mammals, age of, 17. Man, age of, 18 ; relation of, to Na- ture, 286 ; relation of, to animals, 293 ; spirit of, in relation to the forces of Nature, 295, 29S ; rela- tion of God to, 308. Marsupials, 183. I Materialism, relation of, to evolu- tion, 266 ; basis for, in brain-phys- j iology, 288 ; basis for, in evolu- I tion, 293. Methods, scientific, 38. Migration favors diversification, 77. Mind, relation of, to brain, 304, 315 ; versus mechanics in Nature, 317. Mollusks, age of, 16. Monotremes, 183. Mystery, changes in our sense of, 324. Nature, relation of God to, 279 ; im- manence of God in, 282 ; relation of man to, 286 ; has no meaning without spirit, 306 ; mind versus mechanics in, 317. Newton compared with Darwin, 48. Nominalism and realism reconciled, 306. Obstacle to evolution removed, 35. Oceanic island life, 195. Ontogenic series, 9, 40. Or2:anic forms, views of origin of, 29, 68, 72, 274 ; law of continuity applied to, 56. Organs, incipient, 252. Origin of varieties unexplained, 252. Pantheism, true and false, 284, 312. Paroxysmal evolution, 239. Personality of God, 314. Philosophy and life, relations of, 259. Phylogenic series, 10, 41. Planorbis of Steinheira, 236. INDEX. 343 Primal animals, 12Y. Progress of the whole, law of, 13, 22. Progressive change in evolution, 9. Ranges of organic forms, 1G8. Realism and nominalism reconciled, 306. Record, geological, imperfection of, 234. ReUgion, so-called conflict of, with evolution, 45, 262. Religious thought to be reconstruct- ed, 277. Reproduction, methods of, 219. Reptiles, age of, 17. Revelation, relation of evolution to, 308 ; not inconsistent with the laws of Nature, 309 ; nature of, 310. Reversion of artificial forms, 211. Romanes, G. J., his idea of physio- logical selection, 76 ; the idea ap- plied, 227. Rudimentary organs, proofs of evo- lution from, 161 ; organs in man, 163. Selection, sexual, 74 ; natural, 74, 79 ; physiological, 75, 79 ; natu- ral, compared with artificial, 207 ; physiological, applied, 227. Self-consciousness the sign of spirit- individuality, 3C2. Sequoia, 201, 202. Sexes, characters of, compared, 244. Shrimp, external anatomy of, 116. Sin a condition of moral evolution, 332. 16 Skeleton, vertebrate, homologies of, 93 ; articulate, homologies of, 114; articulate, general structure of, 116. Society, progress of, 25. Space and time the two fundamental conditions of material existence, 48. Species, natural, more permanent than artificial varieties, 211 ; more distinct, 214; cross-sterile, 214. Spirit embryonic in animals, 293 ; of man related to anima of ani- mals, 295 ; to forces of Nature, 295, 298 ; no meaning in Nature without, 306. Steinheim, Planorbis of, 236. Taxonomic series, 9, 40. Temperature-regions, 166. Tread, plantigrade and digitigrade, 105. True and the good, relation of, 259. Truth tested by effect on life, 259 ; not compromise, 273. Types, generalized, 13. Use and disuse of organs, 73. Useless structures, how produced, 76. Variation depends on sexual repro- duction, 220; caused by unfavor- able conditions, 246. Varieties, artificial production of, 204, 217; artificial production of, illustrated, 206 ; natural and arti- ficial, compared, 210; origin of, unexplained, 252. su INDEX. "Vestiges of Creation," 34. Virtue and innocence compared, 335. Vital principle, 305. Voluntary social progress, 26. Whales, rudimentary organs of, 162. THE EXD. A LIBRARY OF THE MOST IMPORTANT STANDARD WORKS ON EVOLUTION. I. Origin of Species by Means of Natural Selection, or the Preser- vation of Favored Races in the Struggle for Life. By Charles Dar- win, LL. D., F. R. S. New and revised edition, with Additions. 12mo. Cloth, $2.00. 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"Whoever will follow these pages, crayfish in hand, and will try to verify for himself the statements which they contain, will find himself brous-ht face to face with all the great zoological questions which excite so lively an interest at the present day." "The reader of this valuable monograph will lay it down with a feeling of wonder at the amount and variety of matter which has been got out of so seem- ingly slight and unpretending a subject." — Saturday Eeview. New York: D. APPLETOX & CO., 1, 3, cfe 5 Bond Street. D. APPLETON & CO/S PUBLICATIONS. SUICIDE : An Essay in Comparative Moral Statistics. By Henrt MoRSKLLi, Professor of Psychological Medicine in the Royal Univer- sity, Turin. 12mo. Cloth, $1.75. " Suicide " is a scientific inquiry, on the basis of the statistical method, into the laws of suicidal phenomena. Dealing with the subject as a branch of social science, it con- siders the increase of suicide in different countries, and the comparison of nations, races, and periods in its manifestation. The influences of aiie, sex, constitution, cli- mate, season, occupation, religion, prevailing ideas, the elements of character, and the tendencies of civilization, are comprehensively analyzed in their bearing upon the pro- pensity to self-destruction. Professor Morselli is an eminent European authority on this subject. It is accompanied by colored map.s illustrating pictorially the results of statistical inquiries. VOLCANOES: What they Are and what they Teach. By J. W. JuDD, Professor of Geology in the Royal School of Mines (London). With Ninety-six Illustrations. 12mo. Cloth, $2.00. " In no field has modern research been more fruitful than in that of which Professor Judd gives a popular account in the present volume. The great lines of dynamical, geological, and meteorological inquiry converge upon the grand problem of the interior constitution of the earth, and the vast influence of subterranean agencies. . . . His book is very far from being a mere dry description of volcanoes and their eruptions; it is rather a presentation of the terrestrial facts and laws with which volcanic phenomena are associated."' — Popular Science Monthly. THE SUN. By C. A. Young, Ph. D., LL. B., Professor of Astronomy in the College of New Jersey. With numerous Illustrations. Third edition, revised, with Supplementary Note. 12mo. Cloth, $2.00. The " Supplementary Note" gives important developments in solar astronomy since the publication of the second edition in 1882. " It would take a cyclopaedia to represent all that has been done toward clearing up the solar mysteries. Professor Young has summarized the information, and presented it in a form completely available for general readers. There is no rhetoric in his book; he trusts the grandeur of his theme to kindle interest and impress the feelings. His statements are plain, direct, clear, and condensed, though ample enough for his purpose, and the substance of what is generally wanted will be found accurately given in his pages.' — Popular Science Monthly. ILLUSIONS : A Psychological Study. By James Sully, author of " Sensation and Intuition," etc. 12mo. Cloth, $1.50. This volume takes a wide survey of the field of error embracing in its view not only the illusions commonly regarded as of the nature of mental aberrations or hallucina- tions, but also other illusions arising from that capacity for error which belongs essen- tially to rational human nature. The author has endeavored to keep to a strictly scientific treatment— that is to say, the description and classification of acknowledged errors, and the exposition of them by a reference to their psychical and physical con- ditions. " This is not a technical work, but one of wide popular interest, in the principles and results of which every one is concerned. The illusions of i)ercei)tion of the senses and of dreams are first considered, and then the author passes to the illusions of in- trospection, errors of insight, illusions of memory, and illusions of belief. The work is a noteworthy contribution to the original progress of thought, and may be relied upon as representing the present state of knowledge on the important subject to which it is devoted."— Pp^Jw/ar Science Monthly. New York: D. APPLETON & CO., 1, 3, & 5 Bond Street. D. APPLETON d CO, '8 PUBLICATIONS. THE BRAIN AXD ITS FUJfCTIONS. By J. Luts, Physician to the Hospice de la Salpetriere. With Illustrations. 12mo. Cloth, $1.50. "No livlBg physiolopfist is better entitled to speak with authority upon the structure and functions of the brain than Dr. Luys. His studies on the anatomy of the nervous system are aclj;nowledged to be the fullest and most systematic ever undertaken. Dr. Luys supports his conclusions not only by hie own ana- tomical researches, but also by many functional observations of various other physiologists, includincj of course Professor Ferrier's now classical experi- me'nts."— >Si. James's Gazette. "Dr. Luys, at the head of the great French Insane Asyhim, is one of the most eminent and successful investigators of cerebral science now living ; and he has given unquestionably the clearest and mo?t interesting brief account yet made of the structure and operations of the brain. We have been fascinated by this volume more than by any other treatise we have yet seen on the machinery of sensibility and thought; and we have been instructed not only by much that is new, but by many sagacious practical hints such as it is well for everybody to understand."— TAe Popular Science Monthly. THE CONCEPTS AND THEORIES OF MODERN PHYSICS. By J. B. Stallo. 12mo. Cloth, $1.75. "Judge Stallo's work is an inquiry into the validity of those mechanical con- ceptions of the universe which are now held as fundamental in physical science. He takes up the leading modern doctrines which are based upon this mechanical conception, such as the atomic constitution of matter, the kinetic theory of gases, the conservation of energy, the neDular hypothesis, and other views, to find how much stands upon solid empirical ground, and how much rests upon metaphys- ical speculation. Since the ajjpearance of Dr. Draper's ' Religion and Science,' no book has been published in the country calculated to make so deep an im- pression on thoughtful and educated readers as this volume. . . . The range and minuteness of the author's learning, the acuteness of his reasoning, and the singular precision and clearness of his style, are qualities which very seldom have been jointly exhibited in a scientific treatise."— ^Vei^ York Sun. THE FORMATION OF VEGETABLE MOULD, through the Action of Worms, with Observations on their Habits. By Charles Darwin, LL. D., F. R. S., author of " On the Origin of Species," etc., etc. With Illustrations. 12mo. Cloth, $1.50. " Mr. Darwin's little volume on the habits and instincts of earth-worms is no less marked than the earlier or more elaborate efl'orts of his genius by freshness of observation, unfailing power of interpreting and correlating facte, and logical vigor in generalizing upon them. The main purpose of the work is to point out the share which worms have taken in the formation of the layer of vegetable mould which covers the whole surface of the land in every moderately humid country. All lovers of nature will unite in thanking Mr. Darwin for the new and interesting light he has thrown upon a subject so long overlooked, yet so full of interest and mstruction, as the structure and the labors of the earth-worm.'' — Saturday Review. " Respecting worms as among the most useful portions of animate nature. Dr. Darwin relates, in this remarkable book, their structure and habits, the part they have played in the burial of ancient buildings and the denudation of the land, in the disintegraticm of rocks, the preparation of soil for the growth of plants, and in the natural history of the world." — Boston Advertiser. New York : D. APPLETON & CO., 1, 3, & 6 Bond Street. D. APPLETON & 00/S PUBLICATIONS. A.NTS, BEES, AND WASPS. A Record of Observations on the Habits of the Social Hymenoptera. By Sir John Lubbock, Bart., M. P., F. R. S., etc., author of " Origin of Civilization, and the Primi- tive Condition of Man," etc., etc. With Colored Plates. 12ino. Cloth, §2.00. " This volume contains the record of various experiments made with ants, bees, and wasps during the last ten years, with a view to test their mental condition and powers of sense. The principal point in which Sir John's mode of experiment differs 'rom those of Huber, Forel, McCook, and others, is that he has carefully watched and marked particular insects, and has had their nests under observation for long ptriotls — one of his ants' nests having been under constant inspection ever since lft.74. His observations are made principally upon ants, because they show more power and flexi- bility of mind ; and the value of his studies is that they belong to the department of original research." " We have no hesitation in saying that the author has presented us with the most valuable series of observations on a special subject that has ever been produced, charm- ingly written, full of logical deductions, and, when we consider his multitudinous en- gagements, a remarkable illustration of economy of time. As a contribution to insect psychology, it will be long before this book finds a paraUel." — London At/ienceum. DISEASES OF MEMORY. An Essay in the Positive Psychology. By Th. Ribot, author of "Heredity," etc. Translated from the French by William Huntington Smith. 12mo. Cloth, $1.50. " M. Ribot reduces diseases of memory to law, and his treatise is of extraordinary mieve&i.'"— Philadelphia Press. " Not merely to scientific, but to all thinking men, this volume will prove intensely interesting."— xYew York Observer. " M. Ribot has bestowed the most painstaking attention upon his theme, and nu- merous examples of the conditions considered greatly increase the value and interest of the Moivime:'— Philadelphia North American. "To the general reader the work is made entertaining by many illustrations con- nected with such names as Linnaeus, Newton. Sir Walter Scott, Ilorace Vernet, Gus- tavo Dore, and many others.''''— Harrisburg Telegraph. "The whole subject is presented with a Frenchman's vivacity of style." — Provi- dence Joiirnal. " It is not too much to say that in no single work have so many curious cases been brought together and Interpreted in a scientific manner."— Sos^ow Evening Traveller. MYTH AND SCIENCE. By Tito Vignoli. 12mo. Cloth, $1.50. "His book is ingenious; ... his theory of how science gradually differentiated from and conquered myth is extremely well wrought out, and is probably in essentials correct." — Saturday Review. "The book is a strong one, and far more interesting to the general reader than its title would indicate. The learning, the acuteness, the strong reasoning power, and the scientific spirit of the author, command admiration." — New York Christian Advocate. " An attempt made, with much ability and no small measure of success, to trace the origin and development of the myth. The author has pursued his inquiry with much patience and ingenuity, and has produced a very readable and luminous treatise." — Philadelphia North American. "It is a curious if not startling contribution both to psychology and to the early history of man's development."— iVez^ York World. New York: D. APPLETON & CO., 1, 3, & 5 Bond Street. D. APPLETON & CO/S PUBLICATIONS. Professor JOSEPH LE CONTE'S WORKS. SIGHT s AN EXPOSITION OF THE PRINCIPLES OF MONOCULAR AND BINOCULAR VISION. With numerous Illustrations. 12mo. Cloth, $1.50. •'It is pleasant to find an American book which can rank with the very best of foreign works on this subject. Professor Le Conte has long been known as an original investigator in this department ; all that he gives us is treated with a master-hand."— 7%e Nation. ELEMENTS OF GEOLOGY : A TEXT-BOOK FOR COLLEGES AND FOR THE GENERAL READER. By Joseph Le Conte, LL. D., Professor of Geology and Natural History in the University of California. With upward of 900 Illustrations. New and enlarged edition. 8vo. Cloth, $4.00. A COMPEND OF GEOLOGY : APPLETONS' SCIENCE TEXT. BOOK SERIES. 12ino. Cloth, $1.40. RELIGION AND SCIENCE : A SERIES OF SUNDAY LECT- URES ON THE RELATION OF NATURAL AND REVEALED RELIGION, OR THE TRUTHS REVEALED IN NATURE AND SCRIPTURE. 12mo. Cloth, $1.50. " Professor Le Conte grapples with some of the gravest questions which agitate the thinking world. He treats of them all with dignity and fairness, and in a manner so clear, persuasive, and eloquent, as to engage the undivided attention of the reader. We commend the book cordially to the regard of all who are interested in whatever pertains to the discussion of these grave questions, and especially to those who desire to examine closely the strong foundations on which the Christian faith is reared."— 5ostoft Journal. "This volume is written with much clearness of thought and unusual clear- ness of expression. It is partly a treatise on natural theology and partly a defense of the Bible against the assaults of modem science. In the later aspect the author's method is an eminently wise one. He accepts vvhatever science has proved, and he also accepts the divine origin of the Bible. Where the two seem to conflict, he prefers to await the reconciliation, which is inevitable if both are true, rather than to waste time and words in inventing ingenious and doubtful theories to force them into seeming accord. Both as a theologian and a man of science, Professor Le Conte's opinions are entitled to respectful attention, and there are few who will not recognize his book as a thoughtful and valuable con tribntion to the best religious literature of the day."— iViet/; York World. New York: D. APPLETON & CO., 1, 3, & 5 Bond Street I).^AXXOSTHAIfl» PUBLISHER a IMPORTER OF