Some Recent Aspects of Darwinism

FOR us who have grown up since 1859, the doctrine of the Origin of Species has become so far one of those things quod semper, quod omnibus, quod ubique creditum est, that we waken from our dogmatic slumbers with something of a start to find that, of three recent books which touch upon Darwinism, two are frankly skeptical as to the sufficiency of Natural Selection.

The fact is, however, that the Darwinian, along with his other troubles, has always had to face one serious dilemma. Seeking to discover why, if there must be living beings in the world, there should be so very many different kinds, he seizes — not unreasonably — upon the little differences as the starting-point for the big ones. He sees that, as a matter of fact, no two leaves on the same oak are exactly alike, and no two oaks have just the same average leaf. Almost inevitably he imagines that ten thousand of these minute differences have been lumped together to make the greater ones which distinguish red oak leaves from white. Thus far the Darwinian is one with all evolutionists. He parts company with the others only on the question of causes. Darwin’s great discovery was Natural Selection; a convenient short-hand expression — though, as experience has shown, a very confusing one — for the interaction of several causes, which together integrate little differences into larger ones. The Darwinian, then, attributes a great part of the multiform variety of living beings, and the adaptation of each to its special place in the world, to the continued selection of such small variations as are seen to occur in nature. But, unfortunately for the logic of his case, there are two sorts of these variations. There are, in the first place, those innumerable slight differences which hardly serve to distinguish one creature from another. There are, besides, those occasional and greater unlikenesses between parent and offspring — such as the double paws of the house cat— which it is now the fashion to call discontinuous variations or mutations. If now the Darwinian, called upon to declare which of these two kinds of variation has furnished the raw material for selection, alleges the commoner sort, he is immediately told that no new organ can possibly arise from these, because they are always too small for selection to seize upon. Survival, he is informed, is a matter of real fitness, of having or not having some important quality, not a question of a little more here and a little less there. If, on the other hand, he takes to citing cases of greater departures, he must meet the objection that these are always so few that they are, of necessity, promptly swamped by intercrossing. What if important mutations do occur once in ten thousand times, who can find a trace of any of them after ten generations !

Darwin himself saw this difficulty quite as clearly as anybody. With characteristic disregard of merely formal considerations, he rested his case on the facts. There are, he said in effect, practically these two sorts of variation. Gardeners and breeders have actually used one kind or the other to produce all the countless varieties of pigeons, dogs, horses, cattle, fruits, flowering plants, and the rest. Whatever man has done, Nature has done also, on a larger scale, by the same means. The origin of any particular natural species, or of any prize-winning artificial stock, by selection of one sort of variants or the other, is a matter of detailed evidence, and is not to be discussed on general grounds. It was a case of solvitur ambulando, and on that basis Darwin converted the world. When, however, it came to threshing out the evidence for individual cases, Darwin, in general, put most stress on the commoner sort of variation. When this did not seem to meet the case, he fell back on the other kind in a way that made some of his opponents say that he was playing fast and loose with the whole question, and many of his supporters feel that he had not, after all, quite met the whole difficulty. When all has been said, artificial races are not exactly the same as natural species. Then, too, the analogy between Nature and the gardener and breeder breaks down at the wrong point, since Nature cannot segregate her single favored individual by transplanting it to another bed, or shutting it up in a box stall. In spite, therefore, of a great deal of very ingenious reasoning, the old dilemma, under one form or another, has remained, to be the basis of pretty much every reasonable objection which has ever been urged against Natural Selection, except only those which spring out of that other plague of the Darwinian, the too numerous cases of imperfect adjustment to environment.

For about a generation following the publication of the Origin, writers on evolution were inclined to content themselves with constructing ingenious theories on the basis of Darwin’s evidence, piecing out one untested hypothesis with another, and, in general, following a dialectical method which fairly merited Mr. Bateson’s sarcastic paraphrase : “ ‘ If,’ say we with much circumlocution, ‘ the course of Nature followed the lines we have suggested, then, in short, it did.’ ” As he put the case ten years ago: —

“ So far, indeed, are the interpreters of Evolution from adding to this [Darwin’s] store of facts, that in their hands the original stock becomes even less, until only the most striking remain. It is wearisome to watch the persistence with which these are revived for the purpose of each new theorist. How well we know the offspring of Lord Morton’s mare, the bitch Sappho, the Sebright Bantams, the Himalaya Rabbit with pink eyes, the white Cats with their blue eyes, and the rest! Perhaps the time has come when even these splendid observations cannot be made to show much more. Surely their use is now rather to point the direction in which we must go for new facts.”

The last decade has changed all this. A few of the younger men who have come up since the days of ignorance have turned their backs upon the older questions, and have gone to work on the two great presuppositions of Darwinism, heredity and variation, making them always a question of fact, and not of logic, in a way that would have delighted Darwin’s heart. As a result of this work, unless all signs fail, the next few years should see an advance in the theory of evolution comparable with that which is just now making the physicist the thaumaturgist of science.

Variation is, therefore, except for Darwin’s work, almost a new subject ; so new, that important facts concerning the commonest animals and plants are still ungathered. Indeed, so inconsiderable is the amount which has yet been written from the modern standpoint, and that little is so easily come at, that almost any one who enjoys playing with mathematics, or any amateur gardener with a turn for experimenting, can, with a few months’ reading, put himself in the way of making worthy contributions to science.

Luckily, too, for all writers on heredity and variation, and perhaps still more fortunately for the interest of their readers, the two turn out to be, not, as used to be said, two antagonistic principles, but merely different aspects of the same problem. Nature seems always to be striving to give to each creature seed after its kind. She never quite succeeds, and, in so far as she fails, we call her failure variation. She rarely fails seriously, and such measure of success as she attains we term heredity. A single illustration will serve to show how close the two stand to each other and to everyday life. It must be a matter of common observation that different parts of the body are so correlated that, for example, long arms nearly always accompany long legs, and usually a long face also. Modern standards of accuracy, however, demand something more definite than general impressions that certain things are apt to occur together. So the powerful mathematical analysis, which is perhaps the most distinctive feature of recent work in this field, has yielded, among other things, the index of correlation, a convenient numerical measure of the strength of the tie between the variations of any two organs of the body. On the other hand, the index of correlation for the same organs between parent and offspring is a measure of the force of heredity. Professor Karl Pearson finds that this correlation is least between mother and daughter, somewhat greater between mother and son, greater still between father and daughter, and greatest of all between father and son. Thus it appears — and this is corroborated by other evidence — that men not only transmit more to their children of either sex than do women, but also inherit more even from their mothers ; a striking justification of our immemorial emphasis on inheritance in the male line. Per contra, if women inherit less from their fathers and grandfathers, by so much more are they the daughters of the race. Professor Pearson’s discovery recalls a piece of biological speculation — out of fashion now and much frowned upon in certain quarters — to the effect that males furnish everywhere the variable and progressive element of a species, while the great stream of racial inheritance flows through the females ; a theory which would explain the differences between men and women by supposing that in the one Nature tries her little fliers, in the other, she salts down her gains.

For the anonymous author of Doubts about Darwinism the old dilemma still offers nothing better than a choice of horns on which to spit himself, in spite of all the good work of the last dozen years, with which, to be sure, he shows no very striking acquaintance. Like the worthy clergymen who, a generation ago, used to refute the evolutionists on the basis of a sight acquaintance with the commoner domestic animals, the “ SemiDarwinian ” can only fall back on a special act of creative energy whenever he finds a “ gap.” It is always possible, of course, that the teleologist is right, though even his ready-made explanation has its own difficulties. Teleology, however, is not science ; and there never would have been any science if men had been contented with giving the easy explanation,— as there never was any until they stopped giving it.

For the two naturalists, on the other hand, the way out of the old difficulty lies through the newer studies of inheritance and variation. But the two authors tend so far to opposite opinions on most theoretical questions that they are, in a general way, the spokesmen for the somewhat diverse schools into which students of the double problem are divided by the two sorts of variation. Dr. Vernon gives an account of all important discoveries in variation, heredity, adaptation, and related subjects since Darwin, with so much of Darwin’s own work as is necessary for a background. But while he treats all aspects of the question in due proportion, his chief interest is with the stricter Darwinism which puts most stress on normal variation. Professor Morgan comes to his somewhat unorthodox opinions by way of the remarkable studies in the regeneration of lost parts, an account of which he brought out two years ago. So that his first concern is with the problem of adaptation, where incidentally he disposes most effectively of the teleology of the Semi-Darwinian. For him the study of discontinuous variations and their inheritance has been the most significant aspect of recent work. Both authors, therefore, cover a good deal the same ground ; Professor Morgan with the more critical attitude and the greater interest in the general question, Dr. Vernon with more attention to new facts and methods for their own sake. He assumes that his public is already on reading terms with Darwin, while Professor Morgan begins at the beginning, and devotes half his space to matters which the other takes for granted. Dr. Vernon is, on the whole, the easier reading ; largely because his collection of facts is many times greater ; in some degree because, as a general rule, English men of science write better than Americans. Between the two, modern aspects of organic evolution get pretty well discussed.

But to return to our old dilemma. There is, from the side of continuous variation, a great deal which goes to show that, all theory aside, Natural Selection does seize on small differences which seem to us of no great importance, and does use them to hold one species to its most efficient form, or to modify another to fit a new set of conditions. To take but one example out of many, Dr. Bumpus found that of 136 storm-beaten English sparrows, the 72 that revived differed appreciably from the 64 that died. In general, theaberrantindividuals perished, and those nearest the typical size and shape survived. But besides this, the survivors were shorter and lighter than the others, longer of leg and breast-bone, and larger of skull. Yet who would not have said a priori that half a gram more of average weight would not be rather an advantage than otherwise when it came to weathering a storm, or that a little inferiority in length of leg could possibly make the slightest difference one way or the other ! Still more striking, perhaps, is the case of Mr. Weldon’s crabs, in which Natural Selection is modifying a species under our very eyes. It appears from measurements of thousands of individuals, and after all imaginable precautions for avoiding error, that the small shore crab of Plymouth Sound, England, is growing narrower of body, the ratio of breadth to length falling off about two per cent in five years. This change is due to the selective destruction of the broader individuals under the rapidly changing conditions of their environment. As the water of the Sound becomes dirtier year by year with the growth of the cities near by, the narrower crabs are slightly better able to filter it through their gill-chambers, and have, therefore, by so much the advantage over the others in the struggle for existence. And since their days, on the average, are longer in the water than their competitors’, they leave more descendants to inherit their advantage, with the result that the race, continually recruited from the offspring of the “ fitter ” individuals, is maintaining itself in a situation where many species once common have been exterminated. The obvious conclusion is that here are the beginnings of two new species. Given time enough, there should be a new sparrow to fit American weather, and a new crab to fit the mud of Plymouth Sound. It is easy enough for the philosopher to say offhand that the selection of such little differences can never go beyond the production of local races ; but how, after all, does he know ?

On the other hand, from the side of discontinuous variation, we have learned that almost any plant or animal may suddenly exhibit new characters. A perfect tulip appears with all its parts arranged by fours, when, by all precedent, they should go by threes ; and we men, — who are sometimes thought, very erroneously, to be above all bodily change, — even we are somewhat given to having more ribs or fewer than is thought quite correct, and six or seven digits in place of the usual five. Equally striking facts of the same sort were, of course, known to the older naturalists. But they missed seeing how common they are ; in part, no doubt, because the analysis of the idea of discontinuity had not, in their day, shown that variation may be indefinitely small and yet entirely discontinuous. Size in man, for example, is one of the most variable qualities known, — the dime-museum giant is well up to ten times the weight of the dwarf, — but the variation is continuous, in the sense that all intermediatesizes occur,and those nearest the mean are most numerous. Eye-color, on the other hand, though a very small and unimportant matter, is discontinuous. Nearly all eyes can be assigned at a glance either to the brownblack group or to the gray-blue-green group. Eyes, therefore, are either dark or light, almost never intermediate. Not only, therefore, do we now know that abrupt variation is very much more common than used ever to be suspected, but we have, besides, good reason to think that almost any species, after plodding quietly along for ages, may, all of a sudden, take to varying in the most unexpected manner. Once a species gets to kicking over the traces, the new forms are likely to come with a rush, and the same mutation to appear independently over and over again. De Vries, studying mutations of the evening primrose, found among 50,000 plants in eight generations, 359 of one “ incipient species,” 229 of another, 158 of a third, and smaller numbers of four more, all distinct and self-consistent. Moreover, two of these new primroses grew wild, and maintained themselves under natural conditions unswamped by intercrossing with the stock from which they came.

By all the rules of logic, half-a-dozen plants or animals of a new variety breeding freely with a hundred times their numbers of the older sort ought shortly to disappear. The reason why they do not is that a discontinuous variant is likely to transmit its peculiarity completely, or else not at all. Though Darwin knew this in a general way, the first accurate statement of the matter, like many another fertile idea, came from Mr. Francis Galton. Galton pointed out long ago that there are at least three kinds of heredity, shown conveniently in the transmission of coat-color among horses. If a pure white horse is mated with a pure black one, the colt may follow one parent to the exclusion of the other, and be entirely black or entirely white, the missing color remaining latent, to appear, perhaps, in a subsequent generation. This is alternative or discontinuous inheritance. The latent quality is now termed “ recessive ; ” the other “ dominant.” Or the colt may fuse completely the parental qualities and be gray, — blended or continuous inheritance. Or it may exhibit both colors unblended, as a black and white piebald, — particulate or mosaic inheritance. The observer of mankind will easily recall a sufficiency of cases of the two extreme sorts. We expect children to be blends of the diverse qualities of their parents, and usually do find them a hodgepodge of ancestral characters, — the nose of one, the temper of another, on the average copying their forbears in due proportion ; but as to separate qualities, the heirs of single individuals. Striking physical peculiarities and unusual mental gifts are thought to be very liable to entail, and to come down through half-adozen generations unblended and unimpaired. Good cases of mosaic inheritance are not so common. Eye-color is almost always a discontinuous heritage, but once in a while an iris is flecked with two colors, or marked with two concentric bands, and, more rarely, the two eyes of a pair are not mates.

All these facts had, of course, been known time out of mind. Galton, however, analyzed the matter and provided a terminology. He also taught the world not to mix the evidence for different sorts of inheritance, and he formulated his Law of Ancestral Heredity, the most important contribution to the theory of the subject up to the last year of the nineteenth century. With that year came the final discovery which was to gather up and interpret a thousand scattered facts, the final chapter of a story which began a generation before.

Gregor Mendel was Abbot of Brünn in Moravia when Darwin was at work on the Origin. He does not appear to have had any unusual interest in the problem of evolution ; indeed, his main concern was with an essentially pre-Darwinian question, — the nature of plant hybrids. With this problem as an avocation from his serious clerical duties, the abbot busied himself in the garden of his cloister; a leisurely, clear - headed, middle - aged churchman in whom a great scientist was spoiled. For eight years he experimented with varieties of the common pea, and in 1865 communicated to the Society of Naturalists in Brünn the substance of the discovery which is hereafter to be known as Mendel’s Law, “ the greatest discovery in biology since Darwin.” Unfortunately, at that time, the Brünn Society, like the rest of the world, had other things on its mind. The controversy over Darwin and evolution was then merrily under way, and the world promptly forgot the one thing which was needed to complete Darwin’s work. He, it is clear, never saw Mendel’s paper. If he had, a good many books would have remained unwritten. Mendel himself appears never to have understood the full value of his own idea. Except for one short paper written in 1869 he made no effort to follow the matter out, and devoted the remaining twenty years of his life to theology and the weather, — fields where his great talent for experiment could hardly have had free vent. He died in 1884 with no suspicion that, within twenty years, his modest paper would stand alongside of Animals and Plants and Natural Inheritance, and himself, as a student of heredity, with Darwin and Galton. Somehow or other, Mendel’s discovery escaped attention until four years ago, when De Vries reached it independently. Two years later Mr. Bateson, who had been among the first to realize its significance, made a translation of the two original papers; this, together with his somewhat hasty commentary, is the basis of Professor Morgan’s excellent though brief account, and, in part, of Dr. Vernon’s less satisfactory one. Since then, Mendel’s Law has been found to hold for a considerable number of cases, both among animals and plants, but most unaccountably not to work for a few others ; so that, as yet, no one knows how nearly universal it may prove to be, nor how it is to be reconciled with the older Law of Ancestral Heredity of Galton. Its latest important aspect is an ingenious attempt to apply it to the inheritance of that commonest and most obscure of all discontinuities, — sex.

One illustration will serve to make clear the practical workings of Mendel’s principle. If a single rough-coated guinea-pig of either sex be introduced into a colony of normal smooth-coated individuals, all its offspring of the first generation will be rough-coated like itself. In the next generation, if one of the parents is smooth and the other rough, the young will be half of one sort and half of the other, but if both parents are rough, three quarters will take the “ dominant” rough coat. In the next, and all subsequent generations, one half of those rough-coated individuals which had one smooth-coated grandparent, and one third of those which had two smoothcoated grandparents, which were not mated, will drop out the “ recessive ” smooth-coatedness, and become, in all respects, like their original rough-coated progenitor, even to having only roughcoated young, no matter what their mates may have. Thus Mendel’s Law, though by no means simple, is very precise. The essential part of his great discovery is that in each generation of plants or animals of mixed ancestry, a definite proportion lose one half of their mingled heritage, and revert, in equal numbers, to one or other of the pure types. As a corollary to this there is also the discovery that there may be, as among our guinea-pigs, two sorts of individuals, alike in outward appearance, but fundamentally different in having or lacking a latent quality which, when it exists, becomes patent again in a fixed proportion of their offspring. Apparently in about one case out of two in which Mendel’s Law holds, the new quality or organ of a mutation is “ dominant ” over the old one, like the rough coat of the guineapig over the smooth, and thereby gets a fair chance to prove its fitness for survival.

If Darwin had only known this, how easily he would have disposed of objections based on the swamping effects of intercrossing!

The reader who follows out at length in the pages of our two authors the case which I have outlined here, and realizes that, in spite of all logic, common variations are seized upon by Natural Selection, and uncommon ones not swamped, should be convinced that the horns of the old dilemma are neither so long nor so sharp as they were, and that — always pace the Semi-Darwinian — one set of objections which used to be urged against Darwinism can now be fairly met. But the reader of Professor Morgan will not go very far before he discovers that the Origin of Species by means of Discontinuous Variation is, for him, no part of Darwinism.

Professor Morgan is always a formidable dialectician, and when he gets to running amuck through Sexual Selection, Germinal Selection, Protective Coloration, Mimicry, and the rest, one comes to realize how insecure are the foundations of some parts of our evolutionary science. Here is his unflattering opinion of Sexual Selection : —

“ It is not shown in a single one of the instances that the postulated cause has really had anything to do with the difference in question ; and the attempt to show that the theory is probable, by pointing out the large number of cases which it appears to account for, is weakened to a very great degree by the number of exceptional cases, for which an equally ready explanation of a different kind is forthcoming.”

Weismann, anent the Indian butterfly, Kallima, which looks almost exactly like a leaf, and is the stock case of Protective Mimicry, gets this shrewd thrust: —

“Thus the philosopher in his closet multiplies and magnifies the difficulties for which he is about to offer a panacea. Had the same amount of labor been spent in testing whether the life of this butterfly is so closely dependent on the exact imitation of the leaf, we might have been spared the pains of this elaborate exordium. There are at least some grounds for suspicion that the whole case of Kallima is ‘ made up.’ If this should prove true, it will be a bad day for the Darwinians, unless they fall back on Weismann’s statement that their theory is insufficient to prove a single case.”

Unlike Herbert Spencer and others for whom Natural Selection is inadequate, Professor Morgan does not accept the Inheritance of Acquired Characters ; so that, if the orthodox Darwinians cut rather a sorry figure on his pages, the Lamarckians and other heretics will hardly feel like grinning at their discomfiture.

“ These experiments of Brown - Séquard, and of those who have repeated them, may appear to give a brilliant experimental confirmation of the Lamarckian position ; yet I think, if I were a Lamarckian, I should feel very uncomfortable to have the best evidence in support of the theory come from this source, because there are a number of facts in the results that make them appear as though they might, after all, be the outcome of a transmitted disease, as Weismann claims, rather than the inheritance of an acquired character.” “ Paleontologists have been much impressed by the fact that Evolution has been alongthe lines which we might imagine that it would follow if the effects of use and disuse are inherited. . . . But, as has been said before, it is not this kind of evidence that the theory is in need of, since Lamarck himself gave an ample supply of illustrations. What we need is clear evidence that this sort of inheritance is possible. . . . Why not then spend a small part of the energy, that has been used to expound the theory, in demonstrating that such a thing is really possible? One of the chief virtues of the Lamarckian theory is that it is capable of experimental verification or contradiction, and who can be expected to furnish such proof if not the Neo-Lamarckians? ”

Now while much of this criticism is admirable, coming like a fresh wind of common sense and reality through a region of tinsel and gaslight, much of it also serves but to suggest that in Science, as in Theology, the inclusive Catholic doctrine splits up into the creeds of warring sects, when one article or another is unduly emphasized.

Darwin taught that species arise sometimes by the selection of one kind of variation, or the other, or both ; sometimes by the inheritance of acquired characters ; sometimes by the direct influence of environment; sometimes by discontinuous variation without selection ; and was quite ready to admit any other factor for which there might be evidence in any particular case. Weismann, Wallace, and the Neo-Darwinians, finding that Selection is a good explanation in a large number of cases, straightway conclude that it is the only factor, and are prepared to excommunicate everybody who agrees with Darwin. The Neo-Lamarckians,on the other hand, finding that the direct influence of the environment and the inheritance of acquired characters are often the better explanations, decide that selection is of no particular importance, and set themselves to account for the world without it. Finally enter Morgan, De Vries, and the believers in the new Theory of Mutations, — which is not so very new, — who, because Nature does get ahead per saltum, are ready to shake off the dust of their feet at Neo-Darwinians and NeoLamarckians alike.

However, Professor Morgan is no very violent sectary, and, having once flung selection out at the door, is quite willing to let it in again through the window in half-a-dozen scattered sentences like this, which really concede the whole case: “ From this point of view it may appear, at first thought, that the idea of evolution through mutations involves a fundamentally different view from that of the Darwinian school of selection ; but in so far as selection also depends on the spontaneous appearance of fluctuating variations, the same point of view is to some extent involved, — only the steps are supposed to be smaller.” As if that, after all, were of any great consequence ! I venture, therefore, to interpret the Mutation Theory as a wholesome reaction against the extreme Selectionism of Weismann, and one sign that the world is coming back to the more moderate and saner Darwinism of Darwin. Nevertheless, when all is said, Natural Selection, in some form or other, would be a logical necessity if it were not a matter of fact. Though the future should discover a thousand factors of organic evolution Natural Selection would still be one of them, and Professor Morgan, or anybody else, who attempts to account for the living world without it, will find that, like Alice in the Looking-Glass Country, when he thinks he has at last got out of sight of the house, he is just walking in at the front door.

E. T. Brewster.