Creation by Evolution/Why We Must Be Evolutionists
WHY WE MUST BE EVOLUTIONISTS
By J. Arthur Thomson
Regius Professor of Natural History in Aberdeen University
Evidences of Evolution
We use the familiar phrase “evidences of evolution” with some misgiving, because it does not suggest the right way of looking at the question. Evolution means a way of Becoming. Just as it is certain that all the many races of domesticated pigeon are descended from the wild rock dove, so, it is argued, have all the different kinds of wild animals and wild plants descended from ancestors that were on the whole somewhat simpler, and these from simpler ancestors still, and so back and back until we come to the first living creatures, whose origin is all in the mist. Evolution just means that the present is the child of the past and the parent of the future.
But it is not possible to prove this conclusion in an absolutely rigorous way. We can, indeed, see evolution going on now, but we cannot, so to speak, reverse the world-film and see precisely what took place long ago. The records in the rocks do clearly reveal what happened in the past, even millions of years ago, but not in so clear and so detailed a way as the developing egg of a hen reveals the gradual rise and progress of the chick.
Although we do not know of any competent biologist to-day, however skeptical and inquiring he may be, who has any doubt as to the fact of organic evolution, yet no one would assert that it can be demonstrated as one might demonstrate the law of gravitation, or the conservation of matter and energy, or the development of a chick out of a drop of living matter on the top of the yolk of the egg. But how can a conclusion be accepted without hesitation if it is not rigorously demonstrable? The answer is that the evolution-idea is a master key that opens all locks into which we can fit it, and that we do not know of a single fact that can be said to be in any way contradictory. Like Wisdom, the evolution-idea is justified of its children.
A great zoölogist once said that he was willing to stake the validity of the evolution-idea on the evidence afforded by butterflies, and he was quite right. Any fact about an animal or a plant may be an evidence of evolution when we know enough about it. What makes the general idea of evolution convincing is its satisfactoriness in interpretation. It is always borne out by the facts. We repeat the phrase “the general idea of organic evolution” because this must be distinguished from any particular theory in regard to the factors that have operated in the process. In regard to the factors or causes of evolution there is, and there may well be, difference of opinion among naturalists, for the inquiry is as young as it is difficult; but it is unfair and confused to use this admission of uncertainty as to causes as if it implied any hesitation in regard to the fact of an age-long evolutionary process in which many of the highly finished and very perfect types of animals are shown by the rock record to be preceded by a succession of animals in less finished stages.
There is eloquence in the evidence from the rock record. As ages passed there was a gradual emergence of finer and nobler forms of life. Among back-boned animals the first were the fishes. These led to the amphibians, and these were succeeded by reptiles. Later there arose birds and mammals. Throughout the ages, life has been slowly creeping upward. Detailed pedigrees are disclosed in the rocks, some of them with marvellous perfection, as in the evolution of horses and elephants, camels and crocodiles. For some animals, such as fresh-water snails and marine cuttlefishes, there is an almost perfect succession of fossils, forming a chain in which link 10 is very different from link 1, yet just a little different from link 9, as link 2 is a little different from link 1. For such animals we can almost see evolution anciently at work!
The geographical evidences are also endless. If the present state of affairs is not the outcome of a natural process of evolution, why should the fauna of oceanic islands be restricted to those animals which can be accounted for by transport over the sea by currents and by winds, or on the feet of birds? Thus there are no amphibians on oceanic islands, because few amphibians can endure salt water.
The inhospitable Galapagos Islands are said to be the submerged tops of cold volcanoes, which belong to an ancient peninsula that became first an island and then an archipelago. They have a peculiar fauna, which includes the famous giant tortoises. There are ten different kinds of giant tortoise on ten different islands, and those that are on the islands that are farthest apart are most unlike. There are five different kinds in different parts of the largest island, which is called Albemarle. Now if we consider thoughtfully these facts what can we find them to mean except that isolated groups of one ancient stock of the original peninsula have varied slightly on one or another island and that the isolation prevented any pooling or blending of the new forms? For these large tortoises cannot swim. On Albemarle Island the isolation is probably topographic; it is due to barriers formed by the rugged volcanic surface. When Darwin, as a young man, visited these islands during the voyage of the Beagle he was greatly struck by the fact that each island seemed to have its own kind or species of giant tortoise, and he tells us that he felt himself “brought near to the very act of creation.” This was one of the experiences that made Darwin an evolutionist.
But think also of the anatomical evidence. It is interesting to compare a number of fore limbs—our own arm, a bat’s wing, a whale’s flipper, a horse’s fore leg, a bird’s wing, a turtle’s paddle, a frog’s small arm and a giant giraffe’s at the other extreme. They are very different, and yet when we scrutinise them we find the same fundamental bones and muscles and blood-vessels and nerves. “How inexplicable,” Darwin said, “‘is the similar pattern of the hand of man, the foot of a dog, the wing of a bat, the flipper of a seal, on the doctrine of independent acts of creation! How simply explained on the principle of the natural selection of successive slight variations in the diverging descendants from a single progenitor.” Few zoöogists of today would use Darwin’s words “how simply explained,” for we are aware of factors he did not know of, and some of the factors he believed in very strongly are not unanimously accredited today. But all would agree that the evolution-idea illumines the deep identities, amid great superficial diversities, that are disclosed when we consider, let us say, the classes of backboned animals.
Another anatomical argument is to be found in the frequent occurrence of vestigial structures in animals and in ourselves. Useless dwindled relics of the hind limbs of a whale are found buried deep below the surface. In the inner corner of our eye there is just a trace of what is called the third eyelid, a structure that is strongly developed and readily seen in most mammals, as well as in birds and reptiles. It serves to clean the front of the eye; but although it is big enough to do this in most mammals and birds it is a mere relic in man. Take another example: behind the eye of the skate—a familiar flat fish—there is a large hole called the “spiracle.” It serves for the incoming of the “breathing water,” which washes the gills and passes out by the five pairs of gill-clefts on the under surface. But if we peer into this very useful breathing-hole or spiracle we see a minute comb-like structure, which is the dwindling useless relic of a gill. The cleft or spiracle is of indispensable use to the skate, but the relic or vestigial gill inside the spiracle is of no use at all. Yet it tells us that a spiracle was evolved from a gill-bearing gill-cleft.
One of the most remarkable sets of facts about living creatures—plants as well as animals—is that old structures become transformed into things very new. The poet Goethe helped to make the great discovery that the parts of a flower—sepals, petals, stamens, and carpels—are just four whorls of transfigured leaves, the stamens and carpels being spore-bearing leaves. We sometimes see the whole flower of a flowering plant that has become too vegetative “go back” and become a tuft of green leaves; and it is an unforgettable lesson to pull the flower of the white water lily to pieces and to find that the green sepals pass gradually into white petals, and these gradually into yellow stamens.
Similar lessons are taught by animals. What is the sting of a bee but a transformed egg-laying organ or ovipositor (therefore never found in drones), and what is an ovipositor but a transformed pair of limbs? The elephant’s trunk was a great novelty in its way, but it is just a very long nose with an additional piece due to a pulling out of the upper lip. This is the evolutionary way!
We live in what has sometimes been called the “age of insects,” for of these there are more than a quarter of a million different kinds. Now there must be some meaning in the fact that these can be classified in an orderly way; that one can for many kinds make plausible “genealogical trees.” Often one species, with its varieties, seems to grade into another. In many parts of the animal kingdom there are types that link great classes together. Thus the old-fashioned Peripatus type, a little creature somewhat like a permanent caterpillar, has some worm characters and some centipede characters. It is to some extent a connecting link. The oldest known bird, a fossil beautifully preserved in lithographic stone of Jurassic age, has numerous reptilian features, such as teeth in both jaws, a long lizard-like tail, a half-made wing, and abdominal ribs. Yet it was a genuine feathered bird! And this fossil is unexplainable unless we recognize the fact that this bird had reptilian ancestors.
Very striking, again, are the embryological facts which show that the development of the individual is like a condensed recapitulation of the probable evolution of the race. An embryo bird is for some days almost indistinguishable from an embryo reptile; they progress along the same high-road together; but soon there comes a parting of the ways and each goes off on its own path. The gill-slits of fishes and tadpoles—the slits through which the water used in breathing passes—are persistent in all the embryos of reptiles, birds, and mammals, though in these higher back-boned animals they have nothing to do with respiration. All of them are merely transient passages except the one that becomes the “eustachian tube,” which leads from the ear to the back of the mouth. They are straws which show how the evolutionary wind has blown. In a great many ways the individual animal climbs up its own genealogical tree, but we must be careful not to think that an embryo mammal is at an early stage of its development like a little fish, as some writers have carelessly said. Each living creature, from the very first stage of its development, is itself and no other; and though the tadpole of a frog has for some weeks certain features like that of a fish, especially a larval mudfish, it is an amphibian from first to last. The embryo is the memory of a fish or of a reptile-like ancestor. There is no doubt that the hand of the past is upon the present, living and working; and this is evolution.
Many living creatures today are like ever-changing fountains; they are continually giving rise to something new. The beautiful evening primrose (Oenothera) and the American fruit-fly (Drosophila) are notable examples of changeful types; they are always giving birth to novelties or new forms, technically called "variations" or "mutations"; but the fact of variability is widespread.
In some forms the breeder or the cultivator is able to provoke great changes, for instance, by altering surroundings and food; but he usually has to wait for what the natural fountain of change supplies. This has been our experience with the domesticated animals and cultivated plants that interested Darwin so much. All the domestic pigeons have been derived, under man's care, from the blue rock dove; and there is strong evidence that the multitudinous breeds of poultry are all descended from the Indian jungle-fowl. What Darwin said was this: If man can fix and foster this and that novelty and make it the basis of a true-breeding race, and all in a comparatively short time, what may Nature not have accomplished in an unthinkably long time? And when it was objected: But what is there in Nature corresponding to Man the Breeder, his characteristically Darwinian answer was that the Struggle for Existence implied a process of sifting, which he called Natural Selection. Testing all things and holding fast that which is good or fit: that has been the evolutionary method!
These few examples should make plain the nature of the argument for evolution. It is what is called a cumulative argument. All the lines of facts meet in the same conclusion—the present is the child of the past. There is no conflicting evidence; every new discovery points in the same direction. On many sides we find striking facts, which become luminous when we see them in the light of the evolution-idea. But without that light they are worse than puzzling. All the facts conspire toward the conclusion that animate nature has come to be as it is by a continuous natural process, comparable to that which we can study in the history of domesticated animals and cultivated plants. But we do not give a satisfying account of what has taken place until we can state all the factors that have operated, and that is the subject of the much-debated detailed theories of evolution, like Darwinism and Lamarckism. And even if we were agreed about the factors we should still have to inquire into the meaning or significance of the whole. But that is a religious question.
An Enriching Outlook
Another great reason why we must be evolutionists will come as a surprise to some people. The evolutionist outlook is one that lightens the eyes and enriches us. We are impoverishing ourselves if we shut out the light of evolution. Let us consider three points only.
1. The evolution-idea gives the world of animate nature a new unity. All living creatures are part and parcel of a great system that has moved sublimely from less to more. All animals are blood-relations; there is kinship throughout animate nature.
2. It is indeed a sublime picture that the evolutionist discloses—a picture of an advancement of life by continuous natural stages, without haste, yet without rest. No doubt there have been blind alleys, side-tracks, lost races, parasitisms, and retrogressions, but on the whole there has been something like what man calls progress. If that word is too “human” we must invent another.
3. One of the greatest facts of organic evolution—a fact so great that it is often not realised at all—is that there has been not merely an increase in complexity but a growing dominance of mind in life. Animals have grown in intelligence, in mastery of their environment, in fine feeling, in kin-sympathy, in freedom, and in what we may call the higher satisfactions.
No evolutionist believes that man sprang from any living kind of ape, yet none can hesitate to believe in his emergence —"a new creation’’—from a stock common to the anthropoid apes and to the early “tentative men.” Long ago there was a parting of the ways—it could not be less than a million years ago: the anthropoids remained arboreal and the ancestors of the men we know became terrestrial. So far as we can judge from links that are certainly not missing, but always increasing in number, there were for long ages only tentative men like Pithecanthropus the Erect, in Java, and Eoanthropus, the Piltdown man of the Sussex Weald. Even these were rather collateral offshoots than beings on the main line of man’s ancestry. They were Hominids, but not yet Homo. What trials and siftings there seem to have been before there appeared “the man-child glorious!” Doubtless some great brain change led to clearer self-consciousness, to language, to a power of forming general ideas, to greater uprightness of body and mind; and it is very important to realise that a steady advance in brain development, on a line different from that of other mammals, is discernible in the very first monkeyish animals. Man stands apart and is in important ways unique, but he was not an abruptly created novelty. That is not the way in which evolution works. Man, at his best, is a flower on a shoot that has very deep roots. What the evolutionist discloses is man's solidarity, his kinship, with the rest of creation. And the encouragement we find in this disclosure is twofold. In the first place, though we inherit some coarse strands from pre-human pedigree, it is an ascent, not a descent that we see behind us. In the second place, the evolutionist world is congruent with religious interpretation. It is a world in which the religious man can breathe freely. To take one example: there are great trends discernible in organic evolution, and the greatest of these are toward health and beauty: toward the love of mates, parental care, and family affection; toward self-subordination and kin-sympathy; toward clear-headedness and healthy-mindedness; and the momentum of these trends is with us at our best. And evolution, with these great trends, is going on: Who shall set it limits?
REFERENCES
- Clodd, Edward. Story of Creation.
- Conn, H. W. Method of Creation. 1900.
- Conn, H. W. Method of Evolution.
- Geddes, Patrick, and Thomson, J. Arthur. Evolution. Home University Library. 1911. Geology. Home University Library. 1926.
- Haeckel, Ernst. Natural History of Creation. 1870.
- Jordan, D. S., and Kellogg, V. L. Evolution and Animal Life. 1907.
- Lull, R. S. Organic Evolution. 1917.
- Merz, J. T. History of Scientific Thought in the Nineteenth Century. 1904.
- Metcalf, M. M. Outlines of the Theory of Organic Evolution. 1904.
- Newman, H. H. The Gist of Evolution.
- Poulton, E. B. Essays on Evolution. 1908.
- Romanes, George J. Darwin and After Darwin.
- Thomson, J. Arthur. As Regards Evolution. 1925.
- Weismann, August. The Evolution Theory. 1904.
- Yale University Press. The Evolution of the Earth and Its Inhabitants.
“Invisible, impalpable forces streaming around us and through us; perpetual change and transformation on every hand; every day a day of creation, every night a revelation of unspeakable grandeur; suns and systems forming in the cyclones of Stardust; the whole starry host of heaven flowing like a meadow brook.”—John Burroughs.
“Progressive evolution is the universal plan. Everything which we meet in the world around us, matter and mind, every individual and all congregated masses, begin their course as germs and unfold in slow progression. . . .The faculties of all intelligent creation, all that you call mind, all that you call heart, are framed for an interminable series of evolutions. . . . It is not mainly the mould of this mighty frame of things which establishes it, it is the fact that creation is eternally unfolding new resources and presenting itself under successive and amazing combinations of which no creature in the universe had imagined it capable.”—James McCloud, a Presbyterian Minister of Lexington, Kentucky, in 1818, when Darwin was a small boy.