SEXUAL SELECTION 641 



quired in not a few cases at the cost of increased danger 

 from enemies, and even at some loss of power in fighting 

 with their rivals. The males of very many species do not 

 assume their ornamental dress until they arrive at matur- 

 ity, or they assume it only during the breeding season, or 

 the tints then become more vivid. Certain ornamental ap- 

 pendages become enlarged, turgid, and brightly colored 

 during the act of courtship. The males display their 

 charms with elaborate care and to the best effect; and 

 this is done in the presence of the females. The court- 

 ship is sometimes a prolonged affair, and many males and 

 females congregate at an appointed place. To suppose that 

 the females do not appreciate the beauty of the males, is to 

 admit that their splendid decorations, all their pomp and 

 display, are useless; and this is incredible. Birds have 

 ^ne powers of discrimination, and in some few instances it 

 )an be shown that they have a taste for the beautiful. The 

 females, moreover, are known occasionally to exhibit a 

 marked preference or antipathy for certain individual 

 males. 



If it be admitted that the females prefer, or are un- 

 consciously excited by the more beautiful males, then the 

 males would slowly but surely be rendered more and more 

 attractive through sexual selection. That it is this sex 

 which has been chiefly modified we may infer from the 

 fact that, in almost every genus where the sexes differ, the 

 males differ much more from one another than do the fe- 

 males; this is well shown in certain closely allied repre- 

 sentative species, in which the females can hardly be 

 distinguished, while the males are quite distinct. Birds 

 in a state of nature offer individual differences which would 

 amply suf&ce for the work of sexual selection; but we have 

 seen that they occasionally present more strongly marked 

 variations which recur so frequently that they would im- 

 mediately be fixed, if they served to allure the female. 

 The laws of variation must determine the nature of the 

 initial changes, and will have largely influenced the final 



