Parallel Paths: A Study in Biology, Ethics, and Art

by T. W. Rolleston

“A considerable initial resemblance,” writes Mr. Beddard in his most valuable though somewhat chaotic work on this subject,[76] “may be fairly set down to other causes [than natural selection]; because it is impossible to believe that a slight move in the required direction would be of sufficient importance to serve as material for the action of natural elimination.”

The most convinced Darwinian will hardly deny that the problem involved in this case is a serious one.

Another singular fact to be noted in this connexion is the “conclusion arrived at by the study of mimetic butterflies in all parts of the world—that the females are far more liable to assume this method of defence than the males.”[77] An instance in point, which has been the subject of much discussion, is that of the yellow and black swallow-tailed butterfly, Papilio meriones, found in Madagascar. The island is supposed to be the original home of the species, and here both sexes are much alike. On the mainland of South Africa, however, while the male has undergone the very slight transformations represented by the species P. merope and P. cenea, the females imitate closely three different species of the Danais butterfly which is protected by its disagreeable taste from the usual enemies of the tribe, and which is altogether unlike in shape and coloration to the swallow-tail. “The new forms,” writes Mr. Poulton, “have arisen at so recent a date that many of the intermediate stages can still be seen, while the parent form has been preserved unchanged in a friendly land, where the keener struggle of continental areas is unknown.”[78] The significance of such a fact as this is obvious. If mimicry arose from fortuitous variations of colouring and of form, males alone might show it in some species, females alone in others, and both in yet others, but it is difficult to understand how we could arrive at the actual condition, and find it either common to both sexes or practically confined to the female. If, on the other hand, mimicry and other similar adaptations are ultimately to be interpreted as the common response of the species to the attack of its foes, it is quite natural that the female, as the egg-bearer, the most important factor in the continuance of the species, should be specially protected. It is probable also that she is most in need of protection, as her functions may render her rather more exposed than the male to attack. That natural selection cannot have been the dominant factor in the case we are considering seems clear; for how could it have acted at all without a somewhat vigorous weeding out of unprotected forms? And, in that case, what would have become of the unprotected males of the species?

Difficulties of this kind have, in different cases, been raised again and again since the publication of the Origin of Species, and have had to be answered so often that there seems good prima facie ground for doubting whether they have ever really been answered at all. The strongest advocates of the pure mechanical theory are obliged, as we have seen, to admit that the drift of contemporary scientific opinion is to place little reliance on casual variation and natural selection and to look for the driving force of evolution in other directions.[79] In the introduction to Strasburger’s Text Book of Botany[80] we find this important passage:—

“The tendency is to assume the existence of a development of the organic world due to original, innate capabilities of the living substance and not dependent on selection. The origin of the large subdivisions of the animal and vegetable kingdoms, the ‘Archetypes,’ would be due to this sort of evolution. These archetypes have been, and are still, continually influenced by the environment, and, by their reaction to external conditions, organisms become more or less directly adapted.... The progressive evolution of the archetypes, as well as the direct adaptations to external conditions shown by them, is independent of selection. The latter does, however, exert an influence on the process of evolution of the organic world, though to a much more limited extent than was formerly supposed.”

It is clear that in these original innate capabilities of the living substance we have a power which alone may fully account for the evolution of the organic world, though natural selection can emphasize and hasten its action. Its nature and limits are still undetermined. Biologists are very chary of expressing this power save in terms of chemistry and physics. Men of science are afraid—sometimes I venture to think even morbidly afraid—of opening any door by which the fantastic horde of arbitrary dogmas and superstitions which they have cast out with so much toil and peril might find their way back into the temple of Knowledge. But philosophy must warn them that in shutting out all forces that cannot be weighed and measured in a laboratory they may be shutting out life itself. And those who strenuously insist on reducing nature to a mechanism often find themselves obliged to let in the mysterious life-force by some more or less clandestine entry in order to make their mechanism work. Thus Nägeli, the originator of the theory of heredity which Weismann has developed, attributes the phenomena of growth and evolution not to natural selection but to “internal forces.”[81] He disclaims for these forces any but a physical and chemical significance; but Professor Eimer, in spite of all disclaimers, cannot get rid of the suspicion, well justified in my opinion, that there is in these forces, as conceived by Nägeli, something purposeful and teleological—admit them, he says in effect, and who knows what we shall next be asked to believe?[82] Yet for Eimer himself we find that, as Schopenhauer says, “the lotus of physics is rooted in metaphysics.” Twice in his work on organic evolution, he refers with approval to the view of “our profound philosopher, Oken,”[83] who regarded all existing beings as members or organs of some vast and transcendental organism whose development conditioned theirs. Eimer even makes a somewhat daring application of this principle to a concrete instance in the physical world, one which we have already referred to, the problem of the inheritance of qualities in ants, bees, etc., when these qualities are possessed and exercised only by individuals who cannot transmit them.

“We must regard,” he writes, “the different forms of bees, queens, drones, workers, as discontinuous organs of one whole, which have been evolved from a single indifferent ancestral form.... Only thus can we explain to ourselves the fact that the peculiarities of the workers, notwithstanding that they do not reproduce, are inherited.”[84]

When we are asked to believe in physico-chemical laws of such a nature that they enable the habits of life of a worker-ant or bee to react upon the germ-cells of the queen, just as the exercise of an organ, on Lamarckian principles, affects the reproductive cells of the creature to which it belongs, it becomes plain enough that for modern investigators the so-called mechanical and the so-called psychic conceptions of the universe are really running out at the same point. The gulf between these conceptions, which seemed to yawn so widely after Darwinism, was a mere illusion, arising from a point of view now left behind.

To resume the argument of the foregoing chapters. We have seen that at the basis of all theories of evolution lies the fact of the responsive powers of living protoplasm. But what does it respond to? That is the question of questions. To put it accurately in relation to the process of evolution we must ask, To what do the determinants in the germinal cells of plants and animals respond? To what call did unicellular organisms respond when they first began to interchange chromatin with each other? To what, when they began to divide and form new organisms? To what, when multicellular organisms began to specialize certain cells for reproduction, and these cells to mature themselves for fusion by throwing out half their chromosomes? And when the higher plants and animals came on the scene, reproducing their kind under conditions which make strongly for the fixity of species, how are we to interpret the response of protoplasm when we see organs and structures melt away, and others grow, giving rise to the innumerable types which yield us the existing world with its overwhelming richness and variety of life? Weismann tells us that the response is only to differences in the amount of nutriment obtainable by the various determinants of the germ cell, and has but a fortuitous connexion with the results attained. We have seen the inadequacy of this theory, in the light of the many adaptations such as that of which the fish, Anableps, with its bifocal eyes, and the double sexual organs of terrestrial snails, are types. Lamarck and Darwin, besides the belief in fortuitous variation, held that heritable characters arise from exercise of function. Innumerable cases can be quoted in favour of this explanation, but we have seen instances in which it is absolutely untenable, and yet where the required response takes place just the same. The influence of light and colour tells on the colouring of animals, and impartially protects them when they are preyed upon, or helps them to secure their prey; and this influence is frequently explainable by chemical or electric agencies originating in the environment of the animal, acting on the blood, and thus influencing pigmentation of the skin,[85] but chemistry is helpless to account for the manner in which nature shapes the contour of the wing of a tropical butterfly and paints upon it the veinings of a leaf, or protects a harmless fly by giving it a resemblance to a stinging one, or protects a caterpillar by making it look like a vicious and dangerous reptile. Yet all these protective arrangements are evidently, at bottom, facts of the same order. Protoplasm lives and responds not only discretely in the lowest unit perceptible by the microscope, but collectively in the connected groups of these units called multicellular organisms, and in the disconnected groups of these organisms called species. It really responds not to the exercise of function or to the play of physical forces, but to vital tendencies of the organism. There seems an expansive force in nature which, though working strictly under the dominion of physical laws, is capable of using the combinations brought about by those laws for the preservation and development of life. It is in love with life, it is ever pressing toward action and self-realization, and all roads are one to it if they lead to that end. In it are included the very chemical and physical agencies which it obeys, and also that something beyond which eludes the analysis of the laboratory.