Popular Science Monthly/Volume 48/February 1896/Lord Salisbury on Evolution
|LORD SALISBURY ON EVOLUTION.|
ENTHUSIASTIC adherents have compared the principle of natural selection with the principle of gravitation. The comparison is not warranted. In the first place the one is far from having a like cardinal value with the other as a scientific truth; and in the second place it is not the sole cause of the phenomena to be explained, as Mr. Darwin himself admitted when recognizing the inherited effects of use and disuse. Nevertheless, after making these reservations, I will for a moment adopt the comparison; because, by its aid, I shall be enabled clearly to show the nature of a widely prevalent misconception.
Let us suppose that our days were the days when Newton had lately propounded his theory, and that the newspaper reader (or as there were few such in those days, let us say "the man in the street") had been told about it. Suppose it had been explained to him that, according to Newton, bodies attract one another directly as their masses and inversely as the squares of their distances, and that the phenomena presented by the Solar System had been accounted for by him as conforming to this law. Suppose that presently the man, thus far instructed, learned that there were skeptics: Clairaut, for instance, having found that certain of the Moon's motions could not be explained as results of gravitation, and that consequently Newton's interpretation of planetary motions was untenable. Now suppose the man inferred that along with the theory of gravitation the theory of the Solar System must be abandoned; and that certain views of Copernicus, of which he had heard, and certain other views of Kepler, had been disproved. What, in such case, should we say? Evidently that the man made a profound mistake in identifying the theory of gravitation with the theory of the Solar System. We should say that there were independent reasons for accepting the Copernican system and the laws of Kepler; and that though, were the law of gravitation disproved, the pre-existing theory of the Solar System would lack that rational interpretation which the law of gravitation gave to it, yet it would remain standing on conclusive evidence.
Mr. Darwin's doctrine of natural selection and the doctrine of organic evolution are, by most people, unhesitatingly supposed to be one and the same thing. Yet between them there is a difference analogous to that between the theory of gravitation and the theory of the Solar System; and just as the theory of the Solar System, held up to the time of Newton, would have continued outstanding had Newton's generalization been disproved, so, were the theory of natural selection disproved, the theory of organic evolution would remain. Whether it were shown that natural selection is inoperative, or whether it were shown that though a partial cause it is inadequate to explain all the facts (the inheritance of functionally-wrought modifications being a co-operative cause); or whether it were shown that no cause hitherto alleged is adequate; the general doctrine that organisms of all kinds have arisen by the continual superposing of modifications upon modifications would maintain its place, though it would not be fortified so strongly. Lord Salisbury, however, in common with the immense majority of men, assumes that the hypothesis of organic evolution must stand or fall with its alleged causal agencies. Though in one paragraph he distinguishes between natural selection as an alleged agent, and the facts regarded as implying evolution which are said to be explained by it, yet, at the close of his address, he assumes the two to be so indissolubly connected that, if natural selection goes, evolution must go with it—that the facts are not naturally explicable at all, but must be regarded as supernatural. He says, referring to Prof. Weismann:—"I quite accept the Professor's dictum that if natural selection is rejected we have no resource but to fall back on the mediate or immediate agency of a principle of design." And thus he indorses the popular notion that Darwinism and Evolution are equivalent terms.
Though, speaking on behalf of biologists, who are conscious of the difference, Prof. Huxley, in seconding the vote of thanks, demurred to this identification, yet the above-quoted sentence reappears in the revised and republished form of Lord Salisbury's address.
Absence of direct proof of natural selection is duly emphasized by Lord Salisbury. He says:—"No man or succession of men have ever observed the whole process in any single case, and certainly no man has recorded the observation." And, as direct proof of the hypothesis is not forthcoming, it is tacitly assumed that we must accept the alternative hypothesis, which is equally without direct proof. Here I may be excused if, à propos of this position, I reproduce some passages from an essay published in pre-Darwinian days, when the development hypothesis, as it was then called, was universally ridiculed. The first part of the essay runs as follows:—
Those who cavalierly reject the Theory of Evolution as not being adequately supported by facts, seem to forget that their own theory is supported by no facts at all. Like the majority of men who are born to a given belief, they demand the most rigorous proof of any adverse belief, but assume that their own needs none. Here we find, scattered over the globe, vegetable and animal organisms numbering, of the one kind (according to Humboldt), some 320,000 species, and of the other, some 2,000,000 species (see Carpenter); and if to these we add the numbers of animal and vegetable species which have become extinct, we may safely estimate the number of species that have existed, and are existing, on the Earth, at not less than ten millions. Well, which is the most rational theory about these ten millions of species? Is it most likely that there have been ten millions of special creations [each implying a conscious design and acts in pursuance of it]? or is it most likely that, by continual modifications due to change of circumstances, ten millions of varieties [i. e. kinds] have been produced? . . .
Doubtless many will reply that they can more easily conceive ten millions of special creations to have taken place, than they can conceive that ten millions of varieties have arisen by successive modifications. All such, however, will find, on inquiry, that they are under an illusion. . . . Careful introspection will show them that they have never yet realized to themselves the creation of even one species. If they have formed a definite conception of the process, let them tell us how a new species is constructed, and how it makes its appearance. Is it thrown down from the clouds? or must we hold to the notion that it struggles up out of the ground? Do its limbs and viscera rush together from all the points of the compass? or must we receive the old Hebrew idea, that God takes clay and molds a new creature? . . .Should the believers in special creations consider it unfair thus to call upon them to describe how special creations take place, I reply that this is far less than they demand from the supporters of the development hypothesis. They are merely asked to point out a conceivable mode. On the other hand, they ask, not simply for a conceivable mode, but for the actual mode. They do not say Show us how this may take place; but they say—Show us how this does take place. So far from its being unreasonable to put the above question, it would be reasonable to ask not only for a possible mode of special creation, but for an ascertained mode; seeing that this is no greater a demand than they make upon their opponents.
It is true that the contrast of evidences here emphasized refers not to the theory of the origin of species through natural selection, which at that time (1852) had not been propounded, but refers to the theory of organic evolution considered apart from any assigned causes, or rather, as due to the general cause—adaptation to conditions. The contrast remains equally strong, however, if, instead of the general doctrine the special doctrine is in question; and the demand for facts in support of this special doctrine may similarly be met by the counter-demand for facts in support of the doctrine opposed to it. Perhaps Lord Salisbury will meet this demand by quoting the statements contained in the book of Genesis. But even if, ignoring the skepticism of professed biblical critics, such as the Rev. Prof. Cheyne, he puts absolute faith in these statements current among nomadic groups of shepherds three thousand years ago, he is obliged to admit that these alleged facts are not of the class he refers to when he asks for proof of the hypothesis of natural selection: they are not facts of direct observation.
Thus, supposing the two hypotheses—special creation and evolution by natural selection—are to be tested by the directly observed facts assigned in their support, then, if the hypothesis of evolution by natural selection is to be rejected because there are no directly observed facts which prove it, the hypothesis of special creation must be rejected for the same reason. Nobody has seen a species evolved and nobody has seen a species created.
But now from the question of direct evidence let us pass to the question of indirect evidence. Let us ask if there are any positive facts of observation which tend to justify the one, and whether there are any positive facts of observation which tend to justify the other. Here a comparison leads to widely different results. Familiar though some of the facts are, I must be excused for specifying them, since Lord Salisbury ignores them.
Though, because most of the geological record has been destroyed while the remnant has been dislocated or blurred, and because so small a part—an infinitesimal part—of this remnant has been examined, paleontology furnishes but broken evidence, yet the more the Earth's strata are examined the more they testify that organic forms have arisen by modifications upon modifications. Recent discoveries, especially those which show by intermediate forms that the bird-type is derived from the reptile-type, and those which show that, beginning with the four-toed Orohippus of the Eocene strata, we ascend in later strata, through Mesohippus, Miohippus, Protohippus, and Pliohippus, up to the modern horse, have given strong support to the hypothesis of evolution: support so strong that Prof. Huxley, who had up to the time he saw Prof. Marsh's fossils made reservations in his acceptance of the hypothesis, thereafter accepted it without reserve. Not only do fossils furnish in this and other cases the lines of linear ascent to existing forms, but they simultaneously disclose a general fact of great significance—the fact that early types of creatures in any class display the commonest or most general traits of structure, and that later types of the same class are more specialized in this or that direction: relationships which are necessarily implied by the evolutionary process of divergence and redivergence with accompanying modifications.
The truths of classification, again, have a kindred meaning. Ordinary people, and even naturalists of the old school, pass by as of no significance the remarkable relations which, in both plant and animal kingdoms, exist among their divisions, subdivisions, and sub-subdivisions—classes, subclasses, cohorts, orders, genera, species, varieties. The fact that these fall into groups within groups, successively decreasing in size, consists perfectly with the supposition of common origin. Suppose an arm of a large tree to have been buried in such wise as to leave only the tips of its twigs visible; and suppose a man from the Faroe Isles, ignorant of trees, taking one of these protruding tips for a separate plant, attempted to uproot it. He would find that below the surface the twig he uncovered joined with others like itself to form a small branch; and explorations all around would prove that everywhere the local clusters of twigs thus converged. Further excavations would show that the adjacent branchlets, composed of clusters of twigs, themselves united a little deeper down, and were subdivisions of a medium-sized branch. Again digging he would discover that several such branches formed parts of a still larger branch; and so on continually, until complete clearance made it manifest that all these great branches, small branches, branchlets, and twigs, in their respective groups, had diverged from the one original arm of the tree, which itself had diverged from the stem; and that they formed groups within groups diminishing in size as they became more remote from their common parent. And now observe that while there are thus symbolized the relationships of species, genera, orders, etc., as they now exist, there are also symbolized the relationships which, so far as we know them, exist among remains contained in the Earth's crust: the two sets of phenomena correspond.
The lesson taught by the facts of distribution in Time, is also taught by the facts of distribution in Space. In various regions there are alliances between the present fauna and the past fauna found fossil: though different, they are near akin. It was "this wonderful relationship in the same continent between the dead and the living" which especially forced on Mr. Darwin the belief in descent and modification: this relationship having been demonstrated by Prof. Owen between the existing South American forms and the buried forms of extinct species. The fact that in Australia, long cut off from the other continents, all the indigenous mammals are of the implacental type, and that the fossil mammals found there are also exclusively implacental, illustrates these connections very clearly. And these likenesses of nature between present faunas and past faunas in the same localities are implications agreeing exactly with, the implications pointed out above.
Once more there are the facts of embryology. In various ways these tell us with endless repetition the same story.
Obviously these groups, dividing and subdividing into smaller ones as they diverge and re-diverge, correspond completely to the groups within groups which the classifications of animals and plants show us, and with the groups within groups of the buried branch, which symbolize both their relations and the relations of fossil forms, so far as we know them. That is to say, what we may call the embryological tree corresponds with the classificatory tree, and with those more modern parts of the paleontological tree which we have been able imperfectly to trace. Moreover, if we accept the hypothesis of evolution, the strange transformations undergone by a developing embryo become intelligible, though otherwise unintelligible. Every superior animal commences as a nucleated cell, a form common to the smallest and simplest creatures, the Protozoa. While, among the Protozoa, this nucleated cell, by undergoing fission gives rise to others which part company (which derived cells again divide and part company), the trait common to the Metazoa is that, instead of parting company, the cells formed by successive fissions remain together and constitute a cluster. The members of this cluster divide into two layers, between which, in higher types, there arises a third; and from these all the external and internal organs are formed. In each great class of Metazoa, further development of each higher type is accompanied by a "recapitulation" of traits distinctive of lower types. In the Vertebrata, for instance, the embryo of a bird or a rabbit has, at one time, traits resembling those of the fish-embryo—structures roughly representing gill-clefts being one. And in the case of the human embryo, it is only after exhibiting successive kinships of organization to lower mammals, that it at last assumes the form proper to man. Marvelous as is this repetition of traits belonging to lower types, rudely indicated, it is quite congruous with the hypothesis of evolution—implies a kind of transcendental heredity. On the other hand, the hypothesis of design furnishes no explanation, but presents an insurmountable difficulty. For if the development of the embryo had been divinely arranged, it would surely have gone along lines of direct growth from the germ to the finished form: would not have displayed various metamorphoses having no relations either to passing needs or to ultimate structure and mode of life. With which evidence may be joined the evidence furnished by rudimentary organs, which are full of meaning on the evolution hypothesis, but worse than meaningless in the special-creation hypothesis.
But these four great groups of facts, suggesting in different ways the same history, stand thus far without assigned cause. How come these progressive modifications to have taken place? and why are the modified forms connected with one another in the ways shown alike by paleontology, by classification, by distribution, and by embryology? The reply is that we need only look around to see everywhere at work a general cause which, if it has been at work throughout all time, yields an explanation. Take any plant or animal and expose it to a new set of circumstances (circumstances not so unlike its previous ones as to prove fatal), and it begins to change; and the change is one which eventually adapts it to the new conditions. By what special causes the adaptive modifications are effected does not at present concern us. Here the argument requires us only to recognize the truth that in some way the organization is molded to the new conditions. Though—to illustrations furnished by cultivated plants and domesticated animals—it may be objected that artificial selection has been at work, yet, since artificial selection implies variations, it implies that the selected plants and animals have been modified by external influences, and that the modifications have been inherited and accumulated. And then, if there needs a case in which artificial selection has not come into play, we have a sufficiently striking one in the human race itself. Unless there be adopted the hypothesis (excluded by Lord Salisbury's implied belief) that varieties of men have been independently created, the conclusion is irresistible that their differences have been caused by unlikenesses in their lives carried on in unlike environments. Either their differences are uncaused, which is absurd, or they are differences which have unfitted each variety for its conditions, which is also absurd, or they are differences which have fitted each variety for its conditions; and, if so, they have resulted from the response of the constitution to the conditions themselves: the only supposition which is not absurd. And that this is the necessary interpretation is shown by cases in which—either by the killing off of unfit individuals, or by the effects of habit, or by both—extraordinary adaptations have been produced. There are, as examples, the Fuegians, who in their wretched islands go about naked while the falling snow melts on their bodies; there are the Yakutes—the "iron men," as they are called—who, in their rigorous climate, sleep in the open air and wake covered with hoar-frost; there are the Hindus, constitutionally adjusted to the tropics in such way that they can sleep in the burning sunshine; and, again, there are Indian hill-tribes living comfortably in malarious localities which are fatal not only to Europeans but to Hindus. Moreover, while we thus get proof that organisms fit themselves to their environments, we also get proof that there simultaneously result divergences and re-divergences of races and varieties. Men have spread from some original locality into other localities in all directions; and there have resulted sundry widely unlike families appropriate to their respective habitats, and less unlike breeds diverging within them, such as the Aryan peoples of Europe. This process which the human species shows us is, and always has been, the process with every kind of organism. While we are shown a general cause which has been superposing modifications upon modifications from the beginning, we are also shown how there has arisen a concomitant formation of class within class. The cause we find in operation is a cause of the kind needed to explain the remarkable relations above described.
Thus we have four great groups of observed facts (or five if we include those concerning rudimentary organs) all suggesting the same history, all converging to the same conclusion: their joint significance being immense in comparison with the significance of each group taken by itself. And in the adaptation of organisms to their conditions, directly or indirectly brought about, we have a cause which makes these aggregates of phenomena intelligible. On these mutually-verifying sets of evidences the hypothesis of evolution stands by itself, quite apart from any conclusions respecting its special causes. Hence the meaning of the assertion made above, that even were all theories about the special causes disproved, the doctrine of evolution would remain standing.
And now, having contemplated the observed facts which indirectly support the hypothesis of evolution, let us ask for the observed facts which indirectly support the alternative hypothesis. There are none. Neither in the air, nor on the earth, nor in the water do we find anything implying special creation. Nay, indeed, not only do we see no facts favoring the supposition, but we see a world of facts conflicting with it. From hour to hour incidents showing the uniformity of law and the constant relations of causes and effects generate in us convictions so incongruous with it as to produce instant disbelief of an alleged special creation now occurring. Should any one say that having taken into his room a bowl containing nothing but clear water, he saw a fish suddenly appear in it; or should he say that he had seen near the ground a mass of cloud which, contracting and getting more dense, assumed the form of an unknown animal, what comment should we make? Simply that he was either deluding himself or trying to delude us. We should show by our ridicule that the idea of a special creation, when brought distinctly before us by alleged cases, is too absurd to be entertained.
See, then, the antithesis. While the hypothesis of organic evolution is indirectly supported by great masses of observed facts, the hypothesis of special creation is not only without indirect support from observed facts, but is indirectly contraindicated by the enormous accumulation of observed facts constituting our daily experience.
Striking as this antithesis is, it becomes still more striking when we contemplate the two hypotheses under another aspect. Lord Salisbury implies that in the absence of observed facts directly proving the formation of a species by natural selection, the hypothesis of natural selection can not be sustained. He says:—"I think Prof. Weismann is justified in saying that we can not, either with more or less ease, imagine the process of natural selection"; and he presently implies that in the absence of positive proof the hypothesis of natural selection is "mere conjecture." Let me in the first place point out that Prof. Weismann's meaning is here seriously misrepresented. In the passage Lord Salisbury refers to, Prof. Weismann says of natural selection:—"We accept it—not because we are able to demonstrate the process in detail; not even because we can with more or less ease imagine it [in detail], but simply because we must, etc." And that this is his meaning is proved by the fact that a previous passage to which he refers by the words "as already indicated," runs as follows:—"For it is really very difficult to imagine this process of natural selection in its details." Surely there is an immense difference between the meaning intended and the meaning ascribed. It is perfectly easy to imagine that a flying cannon-ball will presently fall and do damage, while it may be "very difficult to imagine," "in its details," the damage it will do. But, passing over this, let us now consider whether, in the absence of observed facts proving the production of a species by natural selection, we have warrant for the theory of natural selection.
I have always regretted that Mr. Darwin chose this phrase to describe his hypothesis. The word "selection" connotes a conscious process, and so involves a tacit personalization of Nature. By tacitly personalizing that aggregate of surrounding agencies which we call Nature, it introduces vaguely the idea that Nature may select as a human breeder selects—can select and increase a particular quality—which is true only under certain conditions. Further, it raises the thought of choice—suggests the notion that Nature may or may not operate in the alleged way.
It was partly the consciousness that wrong ideas are called up in these ways which led me, when writing The Principles of Biology, to substitute the phrase "survival of the fittest"—partly, I say, because, as is shown in § 164 of that work, the phrase naturally emerges when we contemplate, from a purely physical point of view, the phenomena of life and death in connection with surrounding actions. My belief is that had Mr. Darwin used this phrase, many misunderstandings of his theory would never have arisen, and many objections to his inferences would have been excluded. Among other excluded objections would have been that raised by Lord Salisbury, who thinks that, lacking a basis of observed facts, the hypothesis of natural selection has no basis. For if we substitute the phrase "survival of the fittest," it becomes manifest that the process is a necessary one. To see this it needs but to affirm the opposite and say that the law is survival of the unfittest—that those creatures which were fit to live have died, and those have lived which were unfit to live. These statements embody a contradiction. Hence survival of the fittest is inevitable—is just as certain a truth as a mathematical axiom, which we accept because the negation of it is inconceivable.
Heredity, otherwise manifest, being clearly proved by the experience of breeders, survival of the fittest necessarily implies that those individuals which have structures best adapted to their environments, will, on the average, have better adapted posterity than the rest; and that so the fitness to the environment will be maintained. A further unavoidable corollary is that if the habitat changes in character, or if there occurs a migration to another habitat, the most unfitted will disappear in a greater proportion than the least unfitted; and that from destruction of the most unfitted in successive generations, there will result a continually-diminished unfitness to the new habitat, until there is reached a fitness for it. These are inferences which it is impossible to escape.
Whether by this process a particular variation will be perpetuated and increased, is quite another question. The answer depends on the answer to another question—in what degree, all things considered, does the particular variation conduce to maintenance of life? But while the survival and multiplication of individuals having some advantageous modification of structure, is not a necessary result, the survival and multiplication of individuals having natures, or aggregates of characters, which best fit them to the requirements of their lives, is a necessary result; and it is a necessary truth that this involves the establishment of a varied structure where this in a predominant degree aids them in fulfilling the vital requirements of their lives.
Mark, now, how the strong contrast set forth in the preceding section is thus strengthened. We saw that the evolution-hypothesis is indirectly supported by five great classes of observed facts; and that the perpetual adaptation and re-adaptation of constitution to conditions is a general cause of the kind required to account for these facts. Here we see that, of the special causes which effect adaptation, the chief one, survival of the fittest, is not only one the operation of which we can clearly conceive, but one which it is impossible to conceive as not operating. On the other hand, we saw that there are absolutely no observed facts which yield indirect support to the hypothesis of special creation; but that, contrariwise, all the observed facts of daily experience, proving a constant order among phenomena, negative the hypothesis. And we also saw that while the process of special creation can not be rationally conceived, the negation of it is perfectly conceivable. Thus, bringing the contrast to a focus, it appears that the one is credited both a posteriori and a priori, and the other is discredited both a posteriori and a priori. No stronger contrast in credibility can well be imagined.
Authoritative expositions of the process of natural selection afford no basis for that burlesque of it with which Lord Salisbury amused the public. The Origin of Species does not assume, as a requisite, the chance meeting of similarly varied individuals; and in Chapters III. and VI. of Mr. Wallace's Darwinism, where are assigned evidences which have accumulated since Mr. Darwin wrote, there are described processes quite other than that which Lord Salisbury describes. After referring to artificial selection, and implying that the success of breeders in producing a desired variety depends on their skill "in bringing the right mates together," he goes on to ask:—
Even in the absence of the expositions above referred to, knowledge of familiar facts should have excluded this representation of the requirements. The contents of stud-books and herd-books might have been expected to suffice. It needs but to remember the care with which is specified a descent from some noted sire which lived several generations ago, to recognize the prevailing belief that a variation existing in a particular animal is transmitted in a greater or less degree to posterity, quite apart from the possession of the same variation by the animal with which it is mated; and this belief is held by men who, as breeders, stake large profits on its truth. How, then, can it be said that without the union of two similarly varied individuals, "the new breed would never even begin, let alone the question of its perpetuation after it had begun." And here, to show still more clearly how experience negatives Lord Salisbury's assumption, let me give some evidence furnished not by domestic animals, but by human beings. Referring to a controversy which I have recently been carrying on with Prof. Weismann, Dr. Lindsay Johnson, F.R.C.S., who practices as an ophthalmic surgeon, and who tells me that the experience of other oculists verifies his own, testifies to the transmission of acquired myopia through several generations. He says (I quote with his permission):—
And he sends me a genealogical tree showing that in a family of six children descending from long-sighted ancestry on both sides, four remained normal-sighted, but two, who were miniature painters, became myopic. Of these one, marrying a normal-sighted wife, had two children, of whom one was myopic; and the other, marrying also a normal-sighted wife, had three children, all myopic. Two of these three married normal-sighted wives, and among their children there was in each case one who had become myopic, while the rest are as yet too young to display the defect, for it never occurs until after eight years old. That the inherited trait is in this case one caused by use, and not one arising spontaneously, does not affect the issue. There is proof that a modification of structure existing in one parent may descend to children when no similar modification is possessed by the other parent; and, further, that this modification may be re-transmitted, also without the aid of the second parent: facts which negative Lord Salisbury's assumption.
Let us now consider what is the corollary as respects modification of varieties and formation of species. Travelers tell us that the Bushmen are so long-sighted that they can see as far with the naked eye as a European can with a telescope. Allowing for some exaggeration, it is safely to be inferred that they have marvelous powers of discerning objects at great distances. How has this trait arisen? Small men as they are, wandering about in single families, Bushmen have to guard against enemies, brute and man, and must be ever on the alert to kill or snare animals serving for food. To identify distant moving objects as such or such, is therefore essential to the preservation of life. Here is one who, perhaps from some advantageous variation in the forms of the lenses, or in the adjusting muscles, or in the retinal elements, has vision so keen that he recognizes a man, or a lion, or a springbok, when its distance is half a mile greater than that at which other Bushmen can recognize it. What happens? He is enabled the sooner to take measures for his safety, or to make preparations for a hunt; and in either case has an increased chance of preserving life. By his wife, who has but the ordinary keenness of vision, he has children, some of whom, if not all of whom, inherit this peculiarity; and for the same reasons as before, these have, other things equal, better chances of surviving than the rest. If among their descendants some have the peculiarity in an increased degree, if some inherit it in the same degree, and others in smaller degrees in consequence of intercrossing, there will be a tendency, in virtue of the more frequent survival of individuals who are wholly inheritors or partially inheritors, to increase the distance-vision of the tribe: the stirp will spread more than other stirps. So that even were there no other way of establishing a variation save inheritance from a single varying individual, we may see how it will, if of life-saving efficiency, become established.
But there is another way in which variations become established. Creatures inhabiting the same region as the Bushmen furnish an illustration. The general structure of the giraffe is interpretable only as resulting from the co-operation of both factors in the production of species: the selection of variations and the inheritance of acquired characters. But there is one trait of structure attributable to natural selection alone. The giraffe has a prehensile tongue, almost snakelike in form. This it curls round the small branches of trees and pulls them into its mouth. So that, other things equal, a giraffe with an unusually long tongue is able to obtain twigs and clusters of leaves that are beyond the reach of those not similarly endowed; and, when food is scarce, has an advantage. As with the long-sighted Bushman so with the long-tongued giraffe, descendants wholly or partially inheriting the variation will form a prosperous and increasing stirp. But now observe that besides extraordinary variations there are the ordinary variations—variations such as those occurring in the sizes of the hands among ourselves. Let us suppose the average length of the giraffe's tongue to be one foot, and that there are all degrees of greater lengths up to thirteen inches, and all degrees of smaller lengths down to eleven inches: the numbers above and below the average being assumed equal. In the prehension of the highest branchlets a number of the shorter-tongued will fail where a number of the longer-tongued succeed. As every creature multiplies up to the limits set by the means of subsistence, herds of giraffes must be from time to time underfed. At such times the short-tongued ones must be more underfed than the long-tongued ones. The difference of feeding may not be such as to produce in a direct way greater mortality in the one class than in the other, but it may readily tell indirectly. Especially will there be more deaths of the weaker adults, and the less vigorous young they have produced, when the herd is chased by carnivores. Those which are a yard or two behind the rest lose their lives; and a very small defect in the constitutional state of the adults, or the strength of the young, may entail the slight difference in speed implied. So that, other things equal, more of the short-tongued and their offspring will die than of the long-tongued and their offspring. Hence, without any special choice of mates, it will result that in the next generation the average of length of tongue will be greater. Through subsequent generations the same process will go on increasing this advantageous variation, until some limit is reached at which disadvantages check it, or at which the life-sustaining advantages from some other variation become greater.
So that in the absence of any such improbable events as those Lord Salisbury supposes to be necessary, there are two co-operating ways in which survival of the fittest establishes in a species a useful modification of structure.
The great length of time required for the production of species by the evolutionary process, is supposed by Lord Salisbury to furnish a reason for disbelief. In support of his argument he cites Lord Kelvin's conclusion that life can not have existed on the Earth more than a hundred millions of years. Respecting Lord Kelvin's estimate it may be remarked that the truth of a conclusion depends primarily on the character of the premises; that mathematical processes do not furnish much aid in the choice of premises; that no mathematical genius, however transcendent, can evolve true conclusions out of premises that are either incorrect or incomplete; and that while putting absolute faith in Kelvin's reasonings, it is possible to doubt the data with which he sets out. Suppressing criticism, however, let us accept in full the hundred million years, and see what comes of it. Lord Salisbury argues:—
I will not stop to criticise the assumption that the jelly-fish is a remote ancestor of man; but, accepting all his data, will simply inquire how far Lord Salisbury's conclusion is warranted by them. As introductory to the criticism, I can not do better than quote another passage from the early essay named at the outset: merely remarking that the physiologist referred to as adverse in 1852, would not be thus referred to now. After remarking that those who know nothing of the science of life may naturally "think the hypothesis that all races of beings, man inclusive, may in process of time have been evolved from the simplest monad, a ludicrous one," the passage continues:
Suppose we pursue the comparison indicated in the last sentence. Lord Salisbury invites us to reflect on "the prodigious change" required to transform his hypothetical jelly-fish into a man. He appears never to have reflected upon "the prodigious change" which in a few months transforms the human ovum into an infant. The contrast in structure may not be absolutely as great, since, in the course of the change from infancy to maturity, there is not only increase of size but some increase of structural development. In their essentials, however, the two organizations are alike: differences of proportion and finish chiefly distinguishing them. Let us, then, compare the embryological changes with the evolutionary changes, in their amounts and in the times taken by them. The nine months of human gestation, more exactly stated, is 280 days, that is 6,720 hours or 403,200 minutes. Thus, then, the total change from the nucleated cell constituting the human ovum to the developed structure of the infant just born, is divisible into 403,200 changes each occupying a minute. No one of these changes is appreciable by the naked eye, or even by a micrometer. Turn now to the other member of the comparison. Let us suppose the total change between the primitive Protozoon, or nucleated cell, and the human being proceeding from it, to be divided into increments of change, equal in their number to those gone through by the fœtus. To compare the two sets of changes we divide 100,000,000 years by 403,200. What is the result? We get nearly 250 years as the interval available for an amount of change equal to that which the fœtus undergoes in a minute. Another way of presenting the facts yields results still more striking. Many creatures of superior types take more than a year to reach the reproductive age, and even among insects there are some which retain their larval forms for a longer period. But, bearing in mind that even among the Vertebrata the immense majority of species reach the reproductive age in a year, while some of them, as the inferior Rodents, reproduce in a shorter term, and remembering that throughout the lower divisions of the undetermined phylogenetic series preceding the vertebrates, consisting of relatively small and simple creatures, the succession of generations was probably more rapid, we may fitly, contemplating the whole series, take a year as the equivalent for a generation. If so, it follows that to achieve the transformation of the Protozoon into Man, it requires only that in the space of 250 generations the change shall be as great as that which the human fœtus undergoes in a minute; or, otherwise stating the fact, it requires that each generation shall differ from the last by as much as the fœtus differs from itself after an interval of a fourth of a second.
Should it be urged that the successive stages of the transformation gone through by the infant do not represent fully the stages of transformation gone through in progressing from the primitive nucleated cell to the human being, but that there have been periods of excursive modification on various sides of the direct line, and periods in which there was no advance, or in which there was even some retrogression, it would still result that if, in one generation, there occurred as much change of form as the fœtus undergoes in a minute, the remaining 240 odd generations might be set aside for non-progressive changes: a sufficiently wide margin.
One more misconception embodied in Lord Salisbury's address remains to be noted—not a misconception peculiar to himself, but one which men at large entertain. Speaking of the groups of chemical elements, he says:—
This passage obliges us to infer that Lord Salisbury supposes the theory of evolution to be concerned only with things that "breed." If the molecules of matter were "organic beings," he says, "the comfortable word 'evolution'" might be thought to suggest a solution; but since they are not organic beings, evolution has no place. Apparently, then. Lord Salisbury thinks evolution is concerned only with animals and plants. It is difficult to believe that, well acquainted as he is with the science of the day, he really means that which his words imply. We seem almost bound to assume an inadvertence of expression or a lapse of thought. Still as his statement and his apparent belief have been put before a million or two of readers, it seems needful to do something toward dissipating the misapprehension caused, by briefly indicating what is meant by evolution as rightly understood.
The Cosmos as a whole and in all its parts has reached its present state either supernaturally or naturally; and if naturally then not living things only but all other things have come naturally to be what they are. A doctrine which alleges evolution for the animate world and assumes creation of the inanimate world is absurd. Evolution, if alleged at all, must be alleged as coextensive with all existence—save that which is undergoing the reverse process of dissolution.
One who sees that our interpretations must leave us for ever Ignorant concerning the data of the process—the space and the time, the matter and the motion, as well as the ultimate energy manifested through them—may yet rationally seek a proximate interpretation. If things of all kinds, inorganic, organic, and superorganic, have become what they are, not supernaturally but naturally, the implication is that their present state is the outcome of preceding states; and that the genesis of changes throughout the past has been of like nature with the genesis of changes at present. What, then, is the most dominant trait common to successions of changes?
A thing ever being modified and re-modified diverges more and more from its original condition: accumulated changes produce transformation. What is the general nature of that progressive transformation which constitutes evolution? The first answer to this question was suggested on observing the changes passed through by every unfolding plant and animal. Immeasurably as do the multitudinous kinds of organisms differ from one another, yet the unfoldings of them proceed in similar ways. The detailed changes gone through are infinitely varied, but the general change is the same for all. It has since become apparent that the abstract formula expressing this transformation in all living things, also expresses the transformation which is, and has been, in progress everywhere. The Solar System, in passing from its primitive state to its present state, has exemplified it; and, if we accept Lord Kelvin's conclusion respecting the dissipation of its energy and consequent ultimate fate, it will continue to exemplify it. The transformation of the Earth from those early stages in which its surface began to solidify, down to its present stage, has likewise conformed to the general law. Among living things it is conformed to not only in the unfolding of every organism, but also, if we draw the conclusion pointed to above, by the organic world in general, considered as an aggregate of species. The phenomena of mind, in rising from its lowest forms in inferior creatures up to its form in Man, and again in rising from the lowest human form to the highest, illustrate it. It is again illustrated by the successive stages of social progress, beginning with groups of savages and ending with civilized nations. And we see it no less displayed in all the products of social life—in language, in the industrial arts, in the development of literature, in the genesis of science.
Is this inductive generalization capable of deductive verification? Does this uniformity of process result from uniformity of cause? The answer is—Yes. As the changes universally in progress now and through all past time have resulted in transformations having certain common traits, so also, in the actions everywhere producing them, there are certain common traits. However vast or however minute, every aggregate is like every other aggregate in being subject to the actions of outer things and in having parts that act on one another. Be it the Solar System, which by its motion through space shows that the Stellar Universe around influences it, and which shows that its component bodies influence one another, or be it an infusorium exposed to currents and to living things in the surrounding water, and made up of interdependent organs, we are equally shown that external incident forces affect everything, and that everything is affected by the mutual actions of its parts. But if there is a fundamental unity in the relations of aggregates to their environments and of their components to one another, there must also be a fundamental unity in the processes of change set up in all cases. Hence, then, a certain community of character in the transformations gradually produced. The empirical generalization indicated above as reached by contemplation of phenomena of various orders, becomes a rational generalization on finding that throughout these various orders of phenomena a like cooperation of causes inevitably works out similar observed effects. It is not by accident but by necessity that these transformations of all kinds have common traits.
This is not the place in which to explain and illustrate this universal law of transformation and these universal causes of transformation. Here I am concerned merely to indicate their scope, and to say that the Doctrine of Evolution, rightly conceived, has for its subject-matter not the changes exhibited by the organic world only, but also the changes which went on during an enormous period before life began, and the changes which have gone on since life rose to its highest form, and Man, passing into the associated state, gave origin to the endlessly varied products of social life. It has for its subject-matter the entire cosmic process, from nebular condensation down to the development of picture-records into written language, or the formation of local dialects; and its general result is to show that all the minor transformations in their infinite varieties are parts of the one vast transformation, and display throughout the same law and cause—that the Infinite and Eternal Energy has manifested itself everywhere and always in modes ever unlike in results but ever like in principle.
How utterly different the popular conception of evolution is from evolution as rightly conceived will now be manifest. The prevailing belief is doubly erroneous—contains an error within an error. The theory of natural selection is wrongly supposed to be identical with the theory of organic evolution; and the theory of organic evolution is wrongly supposed to be identical with the theory of evolution at large. In current thought the entire transformation is included in one part of it, and that part of it is included in one of its factors. From his place of vantage Lord Salisbury might have done much to dissipate these delusions; but, unhappily, both his language and his arguments have tended to do the reverse.—Nineteenth Century.
Prof. Weismann proposes germinal selection as the name of a hypothesis supplementary to that of natural selection, by which he explains an apparent protection of useful variations from their first appearance, so that when wanted for natural selection they are always at hand.
- Inaugural Address to the British Association, 1894.
- Carpenter, Principles of Comparative Physiology, p. 474.