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46 COLOR AND SEX. In explanation of these remarkable difierenees of form and habit, we have first Darwin's theory of " sexual se- lection." This is based upon the ardor in love, the cour- age and rivalry of the males, and also upon the powers of perception, taste, and will of the female. The spurs of the male, for example, are supposed to have been developed through the battles of the males. At first a mere knob, they were an advantage to the bird possessing them, enabling him to defeat his rivals. The successful male would be more likely to have offspring who would inherit the tendency of their father to have spurs, and thus, by selection, the unspurred cocks would gradually be replaced by those better armed. This is known as the " law of battle." But the bright colors and gay plumes of the cock have originated, under this theory, through the taste of the female, who, it is assumed, would be more likely to accept the attentions of a bird pleasing in her eye than one who was less strikingly adorned. This has been termed by Lloyd Morgan "■ preferential mating." Wallace has accepted the law of battle as an effective agent in producing certain characters, but considers it natural, rather than sexual selection, and he denies the existence of any important evidence proving female selec- tion. He therefore attributes many secondary sexnal characters to a surplus of vital energy, which, because of a bird's perfect adaptation to the conditions of its exist- ence, can expend itself in the production of bright colors and ornamental plumes ^vitllOut injur}^ to their owners. That is to say, Wallace ascribes to the action of natural selection any secondary sexual character which is of prac- tical use to the male in conflicts with a rival, but denies the female any part in the matter of pairing. Darwin, as I have said, attributes to the female an aesthetic taste which renders the brilliant colors or display of the