210 SEXUAL SELECTION : BIRDS. Part JI, 



Before proceeding, I may remark that under the 

 present and two next classes of cases the facts are so 

 complex, and the conclusions so doubtful, that any one 

 who feels no especial interest in the subject had better 

 pass them over. 



The brilliant or conspicuous colours which charac- 

 terise many birds in the present class, can rarely 

 or never be of service to them as a protection ; 

 so that they have probably been gained by the males 

 through sexual selection, and then transferred to the 

 females and the young. It is, however, possible that 

 the males may have selected the more attractive fe- 

 males ; 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 some 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 exceeded to a slight degree the males 

 in beauty. Exactly the reverse occurs under nature ; 

 for in almost every large group, in which the sexes 

 generally resemble each other, the males of some few 

 species are in a slight degree more brightly coloured 

 than the females. It is again j^ossible that the females 

 may have selected the more beautiful males, these males 

 having reciprocally selected the more beautiful females ; 

 but it is doubtful whether this double process of selec- 

 tion would be likely to occur, owing to the greater 

 eagerness of one sex than the other, and whether it 

 would be more efficient than selection on one side 

 alone. It is, therefore, the most probable view that 

 sexual selection has acted, in the present class, as far 

 as ornamental characters are concerned, in accordance 



