622 THE DESCENT OF MAN 



ever, possible tliat the males may have selected the more at- 

 tractive females ; and if these transmitted their characters to 

 their offspring of both sexes, the same results would follow 

 as from the selection of the more attractive males by the 

 females. But there is evidence that this contingency has 

 rarely, if ever, occurred in any of those groups of birds in 

 which the sexes are generally alike ; for, if even a few of 

 the successive variations had failed to be transmitted to 

 both sexes, the females would have slightly exceeded the 

 males in beauty. Exactly the reverse occurs under nature; 

 for, in almost every large group in which the sexes gener- 

 ally resemble each other, the males of some few species are 

 in a slight degree more brightly colored than the females. 

 It is again possible that the females may have selected the 

 more beautiful males, these males having reciprocally se- 

 lected the more beautiful females; but it is doubtful 

 whether this double process of selection would be likely 

 to occur, owing to the greater eagerness of one sex than 

 the other, and whether it would be more efficient than se- 

 lection on one side alone. It is, therefore, the most prob- 

 able view that sexual selection has acted, in the present 

 class, as far as ornamental characters are concerned, in 

 accordance with the general rule throughout the animal 

 kingdom, that is, on the males; and that these have 

 transmitted their gradually acquired colors, either equally 

 or almost equally, to their offspring of both sexes. 



Another point is more doubtful, namely, whether the 

 successive variations first appeared in the males after they 

 had become nearly mature, or while quite young. In either 

 case sexual selection must have acted on the male when he 

 had to compete with rivals for the possession of the female; 

 and in botti cases the characters thus acquired have been 

 transmitted to both sexes and all ages. But these charac- 

 ters, if acquired by the males when adult, may have-beea 

 transmitted at first to the adults alone and at some subse- 

 quent period transferred to the young. For it is known 

 that, when the law of inheritance at corresponding agea 

 fails, the offspring often inherit characters at an earlier 

 age than that at which they first appeared in their par- 

 ents.'" Cases apparently of this kind have been observed 

 with birds in a state of nature. For instance, Mr. Blyth 

 has seen specimens of Lanius rufus and of Colymhus glaci- 



™ "Tariatioa of Animals and Plants under Bomeaticatlon, " vol. ii. p. 79. 



