212 Heredity. 



the duties of a nurse with exemplary care and vigilance, 

 gently leading back the young to the nest when they 

 stray too far. Yet the male is more brilliantly colored 

 than the female, and his colors are especially brilliant 

 and conspicuous during the breeding season. 



I shall show farther on that the males of domesticated 

 breeds of fowls and pigeons are more conspicuous and 

 diversified than the females, but as fancy pigeons are 

 reared in confinement, and are protected from every 

 danger, this cannot be due to the natural selection of 

 the best-protected females. 



We musk conclude, then, that the brilliant plumage 

 of male birds is due to some more general and funda- 

 mental cause than the one proposed by Wallace, since 

 female reptiles which do not incubate, and female fishes 

 which are even less exposed to danger than the males, 

 and female domesticated birds which are thoroughly 

 protected from enemies, all follow the same law. 



The fact that many structures which are not at all 

 conspicuous are confined, like gay plumage, to male 

 birds, also indicates the existence of an explanation more 

 fundamental than the one proposed by Wallace, and this 

 latter explanation gives no reason why the females of 

 allied species should so often be almost exactly alike 

 when the males are very different. 



Darwin's Explanation. , 



Darwin has given a different explanation, and he 

 believes that the greater modification of males through, 

 out the animal kingdom is chiefly due to sexual selec- 

 tion. He has devoted more than five hundred pages 

 to the development of this idea in his essay on sex- 

 ual selection (Descent of Man, Part II.), and. he has 

 marshalled an overwhelming array of facts with mas- 



