Perhaps the best brief résumé Darwin has made of his views on this subject is given on page 421 of the Descent of Man (London edition, 1885), which may therefore be here cited in full: "If an inhabitant of another planet were to behold a number of young rustics at a fair courting a pretty girl, and quarrelling about her like birds at one of their places of assemblage, he would, by the eagerness of the wooers to please her and to display their finery, infer that she had the power of choice. Now with birds the evidence stands thus: they have acute powers of observation, and they seem to have some taste for the beautiful both in colour and sound. It is certain that the females occasionally exhibit, from unknown causes, the strongest antipathies and preferences for particular males. When the sexes differ in colour or in other ornaments, the males with rare exceptions are the more decorated, either permanently or during the breeding season. They sedulously display their various ornaments, exert their voices, and perform strange antics in the presence of the females. Even well-armed males who, it might be thought, would altogether depend for success on the law of battle, are in most cases highly ornamented; and their ornaments have been acquired at the expense of some loss of power. In other cases ornaments have been acquired at the cost of increased risk from birds and beasts of prey. With various species many individuals of both sexes congregate at the same spot, and their courtship is a prolonged affair. There is even reason to suspect that the males and females within the same district do not always succeed in pleasing each other and pairing.
“What then are we to conclude from these facts and considerations? Does the male parade his charms with so much pomp and rivalry for no purpose? Are we not justified in believing that the female exerts a choice, and that she receives the addresses of the male who pleases her most? It is not probable that she consciously deliberates; but she is most excited or attracted by the most beautiful, or melodious, or gallant males. Nor need it be supposed that the female studies each stripe or spot of colour; that the peahen, for instance, admires each detail in the gorgeous train of the peacock—she is probably struck only by the general effect. Nevertheless, after hearing how carefully the male Argus pheasant displays his elegant primary wing-feathers, and erects his ocellated plumes in the right position for their full effect; or again, how the male goldfinch alternately displays his gold-bespangled wings, we ought not to feel too sure that the female does not attend to each detail of beauty.”
Now it was this very case of the Argus pheasant that first shook Mr. Wallace’s “belief in ‘sexual,’ or, more properly, ‘female’ selection. The long series of gradations by which the beautifully-shaped ocelli on the secondary wing-feathers of this bird have been produced are clearly traced out; the result being a set of markings so exquisitely shaded as to represent ‘balls lying loose within sockets’—purely artificial objects of which these birds could have no possible experience. That this result should have been attained through thousands and tens of thousands of female birds all preferring those males whose markings varied slightly in this one direction, this uniformity of choice continuing through thousands and tens of thousands of generations, is to me absolutely incredible. And when, further, we remember that those who did not so vary would also, according to all evidence, find mates and have offspring, the actual result seems quite impossible of attainment by such means.”
According to Darwin’s own admission (Descent of Man, p. 211), he advanced the theory of Sexual Selection because, in his opinion, Natural Selection did not account for the various ornaments and attractions of the males in question. Mr. Wallace, on the other hand, believes that Sexual Selection does not, while Natural Selection does account for these ornaments; so, in place of Darwin’s view that the beauty of certain male animals leads the females to prefer them to their less ornamented rivals, he substitutes the theory that it is the superior vitality, persistence, and vivacity of the favoured males that fascinate the females, and that masculine beauty is simply a natural result of superior vigour and superabundant health.
Darwin doubtless errs in claiming an æsthetic sense for animals so low in the scale of life as butterflies and other insects, and in attributing to it such extraordinary effects in the development of personal beauty. What Mr. Wallace has done in Tropical Nature is to show simply that it is quite unnecessary to invoke the aid of so questionable an agency as Sexual Selection in order to account for the ornaments of animals; and that the fundamental principle of Darwinism, Natural Selection, accounts for everything.
He maintains that colour is a normal product of organisation, and that not so much its presence as its absence needs accounting for. White and black are comparatively rare and exceptional in nature, while the various tints of red, blue, green, etc., are continually appearing spontaneously and irregularly in the integuments of animals. These irregular colours, if injurious to the species, will be at once eliminated by Natural Selection; but if useful for purposes of identification or protection, they will be preserved and intensified.
Now colour, Mr. Wallace continues, is proportionate to integumentary development, and is most conspicuous in the wings of butterflies and the feathers of birds, for the reason that, just as “the spots and rings on a soap-bubble increase with increasing tenuity,” similarly the delicately-organised surface of feathers and scales is highly favourable to the production of varied colour-effects.
Colour being thus proportionate to integumentary development, we find next that integumentary development is, in turn, proportionate to vigour and vitality; the strongest animals having the largest feathers, scales, horns, etc. Hence the most vigorous and healthy animals are also the most beautiful, the most brilliantly coloured. And this correlation between healthful vigour and beauty is still more strikingly shown in this, that “The colours of an animal usually fade during disease or weakness, while robust health and vigour adds to their intensity. … In all quadrupeds a ‘dull coat’ is indicative of ill-health or low condition; while a glossy coat and sparkling eye are the invariable accompaniments of health and energy. The same rule applies to the feathers of birds, whose colours are only seen in their purity during perfect health; and a similar phenomenon occurs even among insects, for the bright hues of caterpillars begin to fade as soon as they become inactive preparatory to their undergoing transformation. Even in the vegetable kingdom we see the same thing: for the tints of foliage are deepest, and the colours of flowers and fruits richest, on those plants which are in the most healthy and vigorous condition.”
Add to all these considerations that “this intensity of coloration becomes most developed during the breeding season, when the vitality is at a maximum,” and we shall be prepared for Mr. Wallace’s summing up of his case:—
“If now we accept the evidence of Mr. Darwin’s most trustworthy correspondents, that the choice of the female, so far as she exerts any, falls upon ‘the most vigorous, defiant, and mettlesome male’; and if we further believe, what is certainly the case, that these are as a rule the most highly-coloured and adorned with the finest developments of plumage, we have a real and not a hypothetical cause at work. For these most healthy, vigorous, and beautiful males will have the choice of the finest and most healthy females; and will be able best to protect and rear those families. Natural Selection, and what may be termed Male Selection, will tend to give them the advantage in the struggle for existence; and thus the fullest and the finest colours will be transmitted, and tend to advance in each succeeding generation.”
By this strong chain of reasoning (to which my brief >résumé of course cannot do justice) Mr. Wallace shows that Darwin needlessly introduced the principle of Sexual Selection into animal courtship; and at the same time furnishes a new confirmation of Darwin’s compliment that he has “an innate genius for solving difficulties.”
What makes Mr. Wallace’s argument the more cogent is the fact that Darwin himself, in speaking of the lowest classes of animals, explains their beauty on the same principles as those which Mr. Wallace applies to the higher animals. Thus he says: “We can,