Just as man can improve the breed of his game-cocks by the selection of those birds which are victorious in the cockpit, so the strongest and most vigorous males, or those provided with the best weapons, have prevailed in the state of nature over their feebler and more cowardly competitors. Just as man can give beauty, according to his own standard of taste, to his male poultry, by selecting special birds for their plumage, their port, their wattles, or their hackles, so female birds in a state of nature have by a long-continued choice of the more attractive males added to their beauty and their ornamental adjuncts. In these two ways, Darwin believed, a limited selection has slowly developed weapons like the horns of buffaloes, the antlers of stags, the tusks of boars, and the spurs of game-birds, together with the courage, strength, and pugnacity always associated with such special organs. It has also developed the ornamental plumage of the peacock, the argus pheasant, and the birds of paradise; the song of the lark, the thrush, and the nightingale; the brilliant hues on the face of the mandrill; and the attractive perfume of the musk-deer, the snakes, and the scented butterflies. Wherever one sex possesses any decorative or alluring adjunct not equally shared by the other, Darwin attributed this special gift either to the law of battle, or to the long and slowly exerted selective action of their fastidious mates. The germ of the doctrine of sexual selection is to be found, like so many other of Charles Darwin's theories, in a prophetic passage of his grandfather's 'Zoonomia.' Stags, the Lichfield physician tells us, are provided with antlers 'for the purpose of combating other stags for the exclusive possession of the females, who are observed, like the ladies in the time of chivalry, to attend the car of the victor. The birds which do not carry food to their young, and do not therefore marry, are armed with spurs for the purpose of fighting for the exclusive possession of the females, as cocks and quails. It is certain that these weapons are not provided for their defence against other adversaries, because the females of these species are without this armour. The final cause of this contest among the males seems to be that the strongest and most active animal should propagate the species, which should thence become improved.'