When there is talk of evolution among laymen it is because of an interest, first, in the evolution of man — our view of Nature is strongly anthropocentric; second, in the evolution of animals — we all recognize something of their kinship with us; and, third, in the evolution of plants they are farthest away from us. By layman I mean anyone not a working biologist.
The working biologists use evolution all the time as a guide in their work, a determinant of their point of view and method of study, a proved and accepted fundamental fact and principle in the science of living things. Hence the biologist in his relation to evolution is as likely to be interested in the evolution of plants, or in a single group of plants, as in the evolution of animals, or even in the evolution of man — though even biologists are human, and it seems an attribute of humanness to have a prime interest in human beings. But now and then one comes across a naturalist who does seem to be more interested in extra-human Nature than in human nature. Just after the great California earthquake of 1906, which gave scientific men an unusual opportunity to study earthquake ways, the sister of a Western scholar confided to me, somewhat bitterly, of her brother: 'He is no longer a man; he is just a geologist.'
But the layman is always a man, and he sees most importantly in evolution something significant in the problem of the whence, how, and whither of man, and something that must be attended to in developing his world philosophy. Also, and of the same kind and degree of importance, something that has a specific delicate relation to religion, or, at any rate, to theology.
To the mind of the public, evolution has recently assumed again a position of seizing interest. The last time it had such an interest was in the immediate years after the publication of Darwin's Origin of Species. The psychological results of the tremendous cataclysm produced by the war have made men take stock of the status of religion among them. Is religion stronger or weaker because of the war? Or did the realized possibility of such a war, such an unchristian behavior on the part of supposedly Christian peoples, reveal an antecedent and continuing feebleness of religion that must be thoughtfully considered and immediately attended to? Whatever the reason, there has been, since the war, a quickening of attention among us in Europe and America to the status of our religion. And in course of this attention evolution has come again to the position of whipping boy for those who take their religion too emotionally and thoughtlessly, hence violently. If religion is weakened it must be the fault of something and somebody. Putting aside swiftly the uncomfortable thought of the possibility of anything being wrong with religion itself and with its expounders, the fundamentalists see in those black beetles, evolution and Darwin, the disturbing and criminal something and somebody who are guilty of this weakening. Have at them! And Mr. Bryan does.
So here is evolution, especially the evolution of man, again on the defensive. Are we, to go through, all over again, the recital of the classic evidences of the actuality and manner of evolution as read from the four great documents of comparative anatomy, embryology, paleontology, and geographical distribution? And then add to these the confirmatory new evidences that the years since Darwin have brought forth? Must we recall again the fundamental identities, with their obviously adaptive modifications, of the organs and organ-systems of man with those of the other vertebrate and especially mammalian animals the convincing recapitulation in man's embryology of successive conditions of heart and blood-cells and lungs and brain and other organs, which conditions are more or less like the adult conditions of these parts in the successively higher vertebrate classes, the fishes, amphibians, reptiles and birds, and finally, mammals; the occurrence of fossils of prehistoric man from the days of early glacial time, a half-million years ago, up to the near-present, showing the gradual changes in skeletal structure, with their unmistakable implications, the straightening legs and reducing jaw and orbital and occipital crests, and the expanding brain cavity, in a word, the changes from beastliness to humanness; and, finally, the distribution of the living races of man in such a way as to tell the same story as the distribution of the animals and plants? Must all this overwhelming testimony that man is an evolutionary product be rehearsed again because Mr. Bryan says that it does n't exist; or that, if it exists, it need not be taken into account by the truly informed, who have in the book of Genesis a complete manual of world and human origin?
If so, biologists are willing to tell it all over again. But it does seem absurd to have to do it. Especially when there are some other matters concerning evolution that have not been so often retold, and rather need telling and discussion. Sixty years of active study since Darwin, of evolutionary phenomena and of technical discussion among specialists, do not leave evolution just where it was when Darwin and his coadjutors had to drop it. For example, Darwin saw in natural selection a satisfying explanation of the origin of species. We do not see this now. We see in natural selection an important factor in the control of evolutionary lines of plant- and animal-development, and a restraining sieve for the too unfit species, but not a sufficient unaided cause of species-transmutation and -adaptation. There is no mere 'survival of the fittest'; there is a survival of all not too unfit.
But this does not mean returning whole-heartedly to an acceptance of Lamarck's proffered explanation of species-transmutation as caused by adaptive individual modifications and the inheritance and cumulation of these 'acquired characters.' Nor does it mean accepting exclusively the mutations explanation of species origin, despite the general agreement that mutations (rather large, immediately heritable variations) do occur and do make some new, plant and animal forms. Nor, finally, does it mean seeing in, the. Mendelian juggling and recombining of unit characters in the ease of hybridizations a sufficient explanation of new species and adaptive specialization.
What it does mean is that, despite the much additional that has been learned confirmatory of the actuality of evolution, and the new wealth of knowledge that has been gained about the manner and mechanism of some of the principal basic factors of evolution, notably heredity and variation, biologists to-day are less agreed among themselves, or, better put, are more agnostic concerning the causal explanation of evolution now than they were just after Darwin and Huxley had made evolution a household word and natural selection its widely accepted explanation. Of course, natural selection, or Darwinism, never was a unanimously accepted evolution explanation. There were always Lamarckians; but after Weismann, the post-Darwinian champion of Darwinism who out-Darwined Darwin in his insistence on the All-macht of natural selection, had made his fight on the inheritance of acquired characters, Lamarckism went largely into eclipse. Yet there have always been Lamarckians since Lamarck, and are to-day, although there are but few who adhere to Lamarck's own naive form of Lamarckism, with its assumption of the direct inheritance, in photographic replica,' of bodily modifications acquired during the, lifetime of the individual.
The Lamarckians of to-day are Neo-Lamarckians, with various forms of explanation of how parental modifications may cumulate in successive generations by heredity. And new examples of such claimed inherited modifications are every now and then put forward. Among the more recent and important of these claims are those of Kammerer of Vienna; whose accounts of his experiments in inducing changes by environmental influence in the mode of reproduction of various salamanders and in the color of various amphibians and reptiles, with a claimed definite hereditary transmission of these changes in later untreated generations, excited much attention at the last meeting of the British Association for the Advancement of Science. Also those of the Americans, Guyer and Smith, who have reported the positive inheritance of certain eye-defects induced in rabbits by a toxic serum, and whose unusually carefully conducted experiments and elimination of alternative explanations give their claims a very serious importance. And, finally, those of Pavlov the great Russian physiologist, whose white mice, trained to come to their food by the ringing of a bell, produced young who learned their lesson much more quickly, and in turn produced young still more quickly responsive to the signal. However many carelessly claimed instances of modification of species-character by an inheritance of acquired characters can be proved to be uncertain, and thus to be useless as evidence for the Lamarckian explanation of evolution, any single one that cannot be, otherwise explained will have the gravest consequence in the search for the actual causes of evolution.
As a matter of fact, despite the inability of the Lamarckians, or of biologists in general, to offer any indubitable cases of Lamarckian inheritance (unless the most recently advanced cases are of this character), and despite. the heavy weight thrown against the Larmarckian explanation of evolution by almost all that has been learned in the recent years about the physical basis of heredity — in spite of all this, many reputable and thoughtful biologists remain convinced in their own minds that any satisfactory causal explanation of evolution, especially adaptive evolution, must contain as an important fundamental element some form of the Lamarckian assumption. There must be more than just chance variation in successive generations out of which adaptive modification and specialization are to arrive. Almost all the paleontologists believe, on the basis of their knowledge of animal and plant series extending through long periods of time, in some form of orthogenesis, or determinate variation. There must be something, they believe, that drives evolution on in more or less fixed lines, even though these lines lead, as they have led in the case of the crinoids, the ammonites, the great dinosaurs, and various other highly specialized lines, to over-specialization and extinction. Now unless the paleontologists accept some mystic inherent driving factor, such as the Èlan vital, or other, to explain this phenomenon, they must find in environmental influence and the impression on heredity of the changes caused by it, the explanation of the initiation, if not the maintenance, of this evolutionary movement.
Another fact of much significance in connection with adaptive evolution — a fact which I first stressed sixteen years ago in my Darwinism To-day — and which points strongly, to my mind, to some as yet unexplained means of introducing the acquirements of the individual into the heredity of the species, is that many of the inherited species-adaptations of plants and animals are in quite the same direction as the adaptive changes acquired in their lifetime by individuals of closely related species, which may well be the original species from which the newer more adapted ones have branched off. For example, in streams into which hot springs flow individuals of species occurring in the streams may, in the search for place and food, find themselves in warmer and warmer water, and may adapt themselves physiologically, sometimes with slight but recognizable structural changes, to high temperature conditions.
But in the very hot springs themselves may be found species living which show, only in more marked degree, as definite and inherited species characters, the same adaptive changes as those shown by the individuals of the stream species which have found their way into the warmer waters. Similarly, the dwarfed growth of individuals of valley plant-species which have been planted on alpine heights is the same adaptive change as that which has been in some way acquired by typical alpine species, and is now an inherited characteristic of such alpine plants.
Altogether, it may fairly be confessed that evolutionists would welcome the discovery of the actual possibility and the mechanism of transferring into the heredity of organisms such adaptive changes as can be acquired by individuals in their lifetime. It would give them an explanation of evolution, especially of adaptation, much more satisfactory than any other explanation at present claiming the acceptance of biologists. For the truth is, as already suggested, that although we know much more about evolution than we did fifty years ago, and are more than ever sure of the reality of evolution, we are distinctly less confident concerning the causal explanation or explanations of evolution than we were a half-century ago. Darwinism (the selection theories) upset Lamarckism as an explanation; but the new knowledge of variation and heredity largely upsets Darwinism, at least as an explanation of species origin, and at the same time offers no satisfactory replacing explanation. Mutations and Mendelism may explain the origin of new species in some measure, but they do not explain adaptation in the slightest degree.
But it is not with the troubles of the biologists seeking the causes of evolution that the anti-evolutionists concern themselves, although it comes to me with constant surprise that they have not taken more notice than they have of these differences of opinion and questionings on the part of the biologists concerning evolution explanations. But they are not looking for any such small game. The thorough-going anti-evolutionists simply reject evolution outright; they dogmatically assert that there is no evolution; and let it go at that. From a letter just received from a friendly correspondent I quote the following sentences: 'So far as evolution is concerned, it is not an established fact. There is not an established factor supporting it to-day. Oh, how I wish we could get our schoolmen to drop this evolutionary nonsense!'
In answer to this the biologists assert that evolution is scientifically proved. They are quite willing to add that there are many puzzling things about it, the most puzzling thing being its causal explanation. Of course, the biologist might simply be content to say that evolution, like gravitation, exists; that it is a fundamental phenomenon of Nature, which can be described, but not explained. But gravitation can be described or defined in very few words. Evolution cannot be so simply and succinctly described. It has numerous manifestations; it is a complex thing; it is a group of many things. The evolutionist is concerned with the analysis of evolutionary phenomena and an attempt to relate a variety of effects to a satisfying cause. Here is where his puzzles and differences of opinion come in.
Also the relation of evolution to man has so far been a very much more complex and disturbing matter than the relation of gravitation to man. Its significance in relation to the very existence of man is pregnant with opportunities for trouble. Emotions, traditions, old beliefs, religion, and especially formal theology, are involved. Our anthropocentric system of world philosophy, outgrowth of centuries of self-worship, feels itself assailed. The reaction is one of anger and fear. Is man after all not a unique, specially created being, around whom and for whom an all-powerful Creator has produced the rest of life and the world? Evolution comes as the iconoclast to rob man of his sacred isolation. Repulse it; deny it.
This tempest created by a wounded, false self-pride seems unnecessary and rather absurd to the biologist. In the first place, he does not see man robbed by evolution of his high place at Nature's head. In fact, a belief in evolution confirms him in this place. He is still unique, the only thing of his kind or at all closely approaching his kind. His body is no less a wonder-exciting combination of matter and energy because it is composed of natural matter and energy, and is, after all, really a machine or group of machines, and not a mysterious something unrelated to the natural world. His mind is no less an endowment that lifts him far beyond all other living creatures because it reveals in itself basic elements common to the mentality of all life. Nor, finally, does an acceptance of human evolution deny the human possession of spirit, which we all know we have, however unagreed we may be as to how or when we came to possess it.
An evolutionist may be a good man, may be a profoundly religious man, as truly as may a philanthropist or a preacher. Being an evolutionist is not necessarily being any less a man. It is, indeed, being more of a man, if one characteristic of being completely human is the use to the utmost of that noble endowment of intelligence and reason which constitutes the chief special advancement and advantage of man over the lower animals. Evolution makes its appeal to reason, but its acceptance does not mean the abasement, let alone the denial, of emotion, faith, and religion, those great springs of the higher human attitudes and activities.
The evolutionist does not like being called a bad man. He does not like being posted as an enemy of poetry and faith and religion. He does not like being defined, as crassly materialist, a man exclusively of the earth earthy. For, simply as evolutionist, he is not necessarily all or any of these unpleasant things. As individual he may be anything — as anybody else may be. I have known several bad men — one or two of them are in the penitentiary now — who were not evolutionists; who, indeed, even posed and were accepted as very good men, full of faith and religion. One was a Sunday School superintendent. And just as religion and cheating can apparently be compassed in one man, so can one man be both evolutionist and idealist.
What the evolutionist believes, on the basis of a mass of what seems to him unrefuted and irrefutable scientific evidence, is that the plants and animals and man and woman were not created by some sudden supernatural treatment of clay and ribs, but that they have slowly and gradually come into existence through the orderly processes of Nature extending over much time. He sees a fine and awe-inspiring order throughout Nature, some of which can be discovered and, in a measure, understood. He sees in this order, this immense capacity for natural being and doing and becoming, a beauty and majesty in Nature which cannot be transcended in conception. In recognizing the creation of man as its supreme achievement, he sees no belittling of man, but a proof of the extraordinary potentialities of this natural order. In organic evolution he sees just what the name signifies, the unfolding of organized matter, the outrolling of the possibilities of life.
Since the beginning of life on this earth this evolution has led constantly, even if slowly and with retrogressing side branches here and there, or extinctions, now and then, of unadapted or over-specialized kinds of creatures, ever onward and upward to higher life possibilities. It is a grandiose and noble sight which the evolutionist, surveying the natural occurrences of the many long geologic ages through which this earth has passed, as revealed to him by the testimony of the rocks and the accumulated results in the myriad life forms of to-day, sees spread before him. He sees life stretching in a long, continuous, and fascinating series of forms, from simplest, through more and more complex and amazing, to culmination in humankind. He sees even many of the details of the special perfecting of this humankind from its rough and still bestial beginnings of half a million years ago to its present high estate.
With all this in his eyes, is the evolutionist likely to be more blind than other men to the potentialities and possibilities of man himself? He knows no more than other men of the ultimate origin of life itself or of the limitations or lack of limitations of evolution. He sees in evolution the explanation of man's origin and of the character of his present structural and physiological make-up. But of all that is the possession of man, or of all that is the possibility of man, he stands only on even footing with others to learn. If man lives in two worlds, one of his body and one of his soul, the evolutionist, like the rest of us, would like to know it. If imagination and love and faith and religion are something in man's life which are so different from the other things of his life as to call for some other explanation of their existence than the evolution that has given man the special form of his body and manner of its functioning, the evolutionist is not one who cannot be shown it. That there may be a God who has put his Spirit into men, the evolutionist can believe as well as anybody else. There is nothing in the conception of evolution to deny God, or to make man irreligious, or to lessen the aspiration of his soul.
With some naive beliefs in an unnecessary interference with the observed order of Nature on the part of an anthropomorphic God, conceived as behaving in a manner quite too restricted to excite respect, the conception of evolution does cross swords. The evolutionist believes that the description of the origin of earth and life and humankind as given in Genesis is mythological, perhaps allegorical, at any rate not true as a literal account of these happenings. This, however, is something quite distinct from denying God or refusing to see in the Bible a guide to the highest of human conduct and an inspiration to the highest human ideals.
In a word, evolution and the tenets of the Christian religion are not in opposition. They have really little to do with each other. They concern themselves with essentially different affairs. For anti-evolutionists to encourage the popular error that they are incompatibles and even mortal enemies is a crime against both. It leads to .n unnecessary and disastrous confusion in men's minds. It is a blow to human understanding of human life.
The conception of evolution has had an enormous effect on our view and understanding of Nature. It has touched and colored all our natural philosophy. It has introduced irrevocably into our thought two fundamentally important ideas: those of continuity and transmutation in the things of the world. We find evolution, not as an isolated or particular phenomenon in Nature, but something all through and almost identical with Nature. All that we see of the make-up and behavior of living things constantly spells evolution to us. We see change always and everywhere, if we take the long view of Nature. What seems, in the short view, to be rest, or static, reveals itself, when the perspective is lengthened, to be movement, and dynamic. But that is precisely what evolution is: constant, slow, continuous change. Thus it is not too far-fetched to see an identity in Nature and evolution. Certainly that is the impression that the naturalist studying in any field of Nature, studying any phase of Nature, gets. Wherever or to whatever he turns his attention, he sees evolution. It is no wonder, then, that Nature and evolution come to be, to him, nearly synonymous terms.
This is an idea that has been growing on me with the years. More and more I have come to feel that our long-used meaning of evolution is too narrow. To the extent that we understand Nature we understand evolution, and vice versa. There are many, many things about Nature that we do not understand. We do not understand the origin of life or the fundamental cause or causes of its constant flux. We lack a satisfying explanation of such highly specialized adaptations as the extremes of protective coloration, the nest-making habits of the solitary wasps, the extraordinary structural modifications and elaborate life-history of the complete parasites, and, even more baffling, those adaptive specializations which require for their utility very precise reciprocal modifications of structure and habit on the part of two different animal species, as two commensals, or on the part of a plant and an animal, as the orchids and the insects that cross-pollinate them. But these are precisely the things that are the outstanding puzzles in evolution. What we do not understand about Nature we do not understand about evolution; what we do not understand about evolution we do not understand about Nature.
So I want to plead for a wider conception of evolution, a conception as wide as that of living Nature itself. One of the obstacles to the acceptance of evolution has been its particularity. It has seemed to too many to be a special explanation of a few special problems in Nature. To a large part of the general public it has seemed chiefly an explanation of human origin which flies in the face of the Biblical explanation, and hence, by easy implication, is something that denies the Bible, God, and religion. But it is much more than this, and at the same time does not have all the significance attributed to it by the theologians.
It is living Nature, and the way that living Nature has become what it is and will further become what it will be.
Considered, and I think justifiably, in this large way, evolution is not to be denied so categorically and completely as my correspondent would deny it. To deny evolution in toto seems to me like denying the fact of life itself, life plastic, changing, adapting, perfecting; life not created once for all in rigidly fixed form, but developed and ever developing slowly, wisely, or at least as if it had wisdom, or was guided by wisdom, in the way and ways which lead to constant betterment. This is how evolution seems to me to be revealed by, the study of Nature; this is what evolution seems to me to be.
Well, this is also what living Nature itself seems to be: a slow, mighty, constant movement of matter and energy, showing itself in ever-changing form and behavior, and revealing potentialities and possibilities that seem limitless. Man is a part of this Nature; hence, is endowed with these limitless potentialities. In this lies the basis of a religion of hope and inspiration. In whatever varying terms various ones of us name or personify the limitless potentiality of Nature and man, that need make no disturbing difference in our common acceptance of this fundamental basis of our religion. It need not make us less good or less honest. It need not undermine our belief in and practice of love and charity; it need not make us have lesser visions or smaller faith. It can magnify our conception of Nature, confirm our confidence in the limitless possibilities of life, and exalt our hopes for the future of humankind. Is this a form of religion to be banned?