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_.