almost entirely of very simple sensuous factors. In order for a butterfly or a humming-bird to admire its gorgeously appareled mate, it is not necessary that it should be capable of taking delight, like ourselves, in a Claude or a Rubens; it is enough that it should possess a nervous organization pleasurably affected by certain forms and colors in the same way as it is pleasurably affected by sweet fruits or the nectar of flowers. Nothing more than this need be postulated in order to establish the facts for which Mr. Darwin has contended with such wealth of illustration in the second part of the "Descent of Man."
It may be worth while, then, to examine a single large class of animals, in which the æsthetic nature is highly developed, for the purpose of discovering whether they do really afford proof of a sensibility to form, color, or musical sound. It must be remembered that even in our own race the sense of beauty in children, savages, and the uncultured classes, hardly rises above this simple level. We must not, of course, expect to find an appreciation of musical harmony, of imitative pictorial skill, of elaborate ornamentation, among birds or insects. We must be content if we see evidence of a love for red, blue, and yellow, for sweet perfumes and pleasant flavors, for symmetrical forms and simple patterns, for ringing notes and trilled resonances. The class of birds probably shows external marks of such tastes in a higher degree than any other; and, though many of them have been set forth by various writers elsewhere, it will perhaps repay the trouble to collect them into a single paper in order to show their bearing upon the general æsthetic sensibility of the class, as well as upon the specific question of sexual selection. For this purpose I shall first take for granted the fact of such selection, and afterward endeavor to justify it by analogy from known human practice.
Beginning with the lowest of the special senses, taste, we find ample evidence that very many birds have a strong liking for sugar. In confinement, canaries and parrots eagerly devour it in the manufactured form. In the wild state humming-birds, sun-birds, honey suckers, lories, and many other species, feed off the nectar of flowers, more or less mixed with insects. Mr. Webber, an American naturalist, found that the ruby-throats of the United States were attracted by a cup of sirup, and numerous other birds display a strong liking for the same mixture. Fruits, which have been developed especially to suit the tastes of birds, almost always contain an abundance of sugary juices; while the kernels within their stones are generally bitter, so as to prevent their winged allies from devouring the actual seed. Hence we may infer that all the vast tribes of toucans, hornbills, macaws, plantain-eaters, birds-of-paradise, and fruit-pigeons, possess a taste for sugar sufficiently strong to have produced the separate evolution of these sweet seed-coverings in a hundred different families of plants throughout the whole world. Indeed, the strength of the evidence thus afforded can not be overrated, when we remember that
