(c) Individual Preference.—Owing to our scant information concerning the courtship of animals in a state of nature, Darwin did not succeed in discovering any cases among mammals of decided preference shown by a male for any particular female; and regarding domesticated quadrupeds, “The general impression amongst breeders seems to be that the male accepts any female; and this, owing to his eagerness, is, in most cases, probably the truth.” A few cases of special preference or antipathy in dogs, horses, bulls, and boars, were, however, communicated to him. Concerning birds Darwin remarks that “In all ordinary cases the male is so eager that he will accept any female, and does not, as far as we can judge, prefer one to the other, but ... exceptions to this rule apparently occur in some few groups. With domesticated birds, I have heard of only one case of males showing any preference for certain females, namely, that of the domestic cock, who, according to the high authority of Mr. Hewitt, prefers the younger to the older hens.”
This, however, is at best only a polygamous sort of Preference, which, after all, lacks the essential traits of Individualisation and Exclusiveness. With the long-tailed duck (Harelda glacialis), M. Ekström says, “It has been remarked that certain females are much more courted than the rest. Frequently, indeed, one sees an individual surrounded by six or eight amorous males.” Whether this statement is credible Darwin does not know; but the Swedish sportsmen, he adds, shoot these females and stuff them as decoys.
In female animals, on the other hand, the “overtone” of Individual Preference appears to be more frequently present. Darwin even asserts that “the exertion of some choice on the part of the female seems a law almost as general as the eagerness of the male;” but this is not borne out by the numerous illustrations given by himself, showing that when two or more males are engaged in jealous combat, “the female looks on as a passive spectator,” and finally goes off with the victor, whichever of the rivals he may prove to be, without showing the slightest concern for the vanquished. An Australian forest-maiden might behave similarly under these circumstances, but a civilised maiden would cling to the one who had made the deepest impression on her previous to the combat; and if wounded, would adore him all the more; for in her Love pity is a stronger ingredient than even the love of prowess.
That female birds, however, sometimes exert a choice is admitted even by Mr. A. R. Wallace (Tropical Nature, p. 199); and a few of the cases referred to by Darwin may here be cited: “Audubon—and we must remember that he spent a long life in prowling about the forests of the United States and observing the birds—does not doubt that the female deliberately chooses her mate; thus, speaking of a woodpecker, he says the hen is followed by half a dozen gay suitors, who continue performing strange antics ‘until a marked preference is shown for one.’ The female of the red-winged starling (Agelæus phœniceus) is likewise pursued by several males, ‘until, becoming fatigued, she alights, receives their addresses, and soon makes a choice.’ He describes also how several male nightjars repeatedly plunge through the air with astonishing rapidity, suddenly turning, and thus making a singular noise; ‘but no sooner has the female made her choice than the other males are driven away.’”
Concerning domesticated birds we have seen that that gallinaceous sultan, the domestic cock, shows a decided preference for the younger hens in his harem. But the female is not a bit less frivolous and capricious; for, according to Mr. Hewitt, she almost invariably prefers the most vigorous, defiant, and mettlesome male; hence it is almost useless, he adds, “to attempt true breeding if a game-cock in good health and condition runs the locality, for almost every hen on leaving the roosting-place will resort to the game-cock, even though that bird may not actually drive away the male of her own variety.”
(d) Personal Beauty and Sexual Selection.—Mr. Wallace, who discovered the law of Natural Selection independently of Darwin, admits, as just stated, that “in birds the females do sometimes exert a choice”; but he adds that “amid the copious mass of facts and opinions collected by Mr. Darwin as to the display of colour and ornaments by the male birds, there is a total absence of any evidence that the females admire or even notice this display. The hen, the turkey, and the pea-fowl go on feeding while the male is displaying his finery; and there is reason to believe that it is his persistency and energy rather than his beauty which wins the day.”
Briefly stated, the difference between the views of these two eminent naturalists is this: Darwin believes that in those cases where the sexes are not alike, the differences are due to the males, originally plain, having become modified through Sexual Selection for ornamental purposes; while Mr. Wallace believes that colour is a normal product in animal integuments, proportionate to their vitality, and that the sexual differences in ornamentation are due to the females having been modified through Natural Selection for the sake of protection.
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.”