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.