CHAP. X.] SEXUAL SELECTION. 319 



males as happened most to resemble the females of another 

 species ! 



From the foregoing facts and considerations it seems to 

 follow that we must of necessity admit the action of some 

 internal force. It cannot be pretended that there is any 

 evidence for sexual selection except in the class Birds. 

 Certain of the phenomena which Mr. Darwin generally 

 attributes to such selection must be due to other causes, 

 and there is no proof that sexual selection acts, even amongst 

 birds. 



But in other classes, as we have seen, sexual characters 

 are as marked as they are in the feathered group. Need of an 



~r\ internal 



Thus, with regard to certain apes, Mr. Darwin force. 

 himself says, &quot; Several authors have used the strongest 

 expressions in describing these resplendent colours, which 

 they compare with those of the most brilliant birds &quot; (vol. ii. 

 p. 293). And yet there are no grounds for believing that 

 female apes select, while there are very strong reasons 

 against a belief in the exercise of any such selective action. 

 Mr. Darwin, indeed, argues that birds select, and assumes 

 that their sexual characters have been produced by such 

 selection, and that, therefore, the sexual characters of beasts 

 have been similarly evolved. But we may turn the argu 

 ment round, and say that sexual characters not less strongly 

 marked exist in many beasts, reptiles, and insects, which 

 characters cannot be due to sexual selection ; that it is, there 

 fore, probable the sexual characters of birds are not due to 

 sexual selection either, but that some unknown internal 

 cause has equally operated in each case. The matter, in 

 deed, stands thus. Of animals possessing sexual characters 

 there are some in which sexual selection cannot have acted ; 

 others in which it may possibly have acted ; others again 

 in which, according to Mr. Darwin, it has certainly acted. 

 It is a somewhat singular conclusion to deduce from this 

 that sexual selection is the one universal cause of sexual 

 characters when similar effects to those it is supposed to 

 cause take place in its absence. 



