Darwin, as we know, was the great demonstrator—though not the first conceiver—of the law of natural selection,[118] and on this he might have cried “_Nunc dimittis_” and retired, so to speak, leaving someone else to find out the other law; but instead of that he went on and demonstrated that too. This other law, the evidence for which is really overwhelming, and has never been met by anything better than a conceited over-estimation of human superiority, wrapped up in a cloud of wrong reasoning, is that of sexual selection, which implies that, in the choice of their mates, animals, like ourselves, are guided by some sort of preference; and as this with them—again like ourselves—is usually determined by the element of beauty, the most beautiful partners are being constantly selected, and species in consequence become more and more beautiful. This process, however, is usually confined to the males, they being the eager wooers, whilst the females only wait to be courted, and then shyly and modestly choose—such, at least, is the supposition. This masculine beauty is often inherited by that sex only to which it is so useful, but in other cases it is transmitted to the female also. Thus, to take birds, where the results of the law of sexual selection are on the whole most pronounced, we have, on the one hand, the pheasants and birds of paradise, where the male alone is resplendent, whilst in the trogons, parrots, and many other species the beauty is common to both the sexes. As is well known, the males of various highly ornate birds are accustomed to make the most extraordinary display of their beauty before the females, making the most of the parts most richly decorated, assuming just such attitudes as are required in order to give these their full advantage, and, in fact, taking pains and trouble in a high degree and of a very special and peculiar kind, which must either be directed to an end which seems perfectly plain and apparent, or else so much waste of time—due to no special cause and without any particular meaning—an alternative which the opponents of sexual selection do not in the least mind accepting.