For other arguments which may be advanced against Mr. Darwin’s theory of sexual selection, reference may be made to Mr. Wallace’s criticisms in ‘Tropical Nature’ and ‘Darwinism.’ We have sufficient evidence that females are pleased or excited by the males’ display of their sexual colours,[1512] and are charmed by their songs. But Mr. Darwin’s theory presupposes, amongst many other things, that almost all the females of a species, over a wide area and for many successive generations, prefer exactly the same modification of the colour, or ornament or sounds.[1513] Moreover, if the secondary sexual characters are due to female choice, how shall we explain the strange fact that the taste of the females varies so much that there are scarcely two species in which the standard of perfection is exactly the same? This difficulty did not escape Mr. Darwin. “It is a curious fact,” he says, “that in the same class of animals sounds so different as the drumming of the snipe’s tail, the tapping of the woodpecker’s beak, the harsh trumpet-like cry of certain waterfowl, the cooing of the turtle-dove, and the song of the nightingale, should all be pleasing to the females of the several species.” And further, “What shall we say about the harsh screams of, for instance, some kinds of macaws; have these birds as bad taste for musical sounds as they apparently have for colour, judging by the inharmonious contrast of their bright yellow and blue plumage?”[1514] The theory now suggested accounts fully for this difference in taste. The immense variability of the secondary sexual characters is precisely what might be expected, if their object is to make it easier for the sexes to find and recognize each other. And it is natural that the females should be pleased by colours, odours, or sounds which, by the association of ideas, are to them the symbols of the most exciting period of their lives. On the other hand, we know that differently coloured races of the same species may be disinclined to pair together.[1515] And here, I think, we may draw an important conclusion. The great stability of the secondary sexual characters which we find in wild species, but certainly not in animals under domestication, seems to be due chiefly to the fact that those males which most typically represent the peculiarities of their species have the best chance of finding mates. * * * * *