The Descent of Man 19 



iilly more sober plumage of the hens has been produced by 

 natural selection, killing off the more brilliant ones exposed 

 during incubation to trying conditions. 



Now as Mr. Wallace disposes of Mr. DarAvin's views by his 

 objections, so Mr. Darwin's remarks tend to refute Mr. Wal- 

 lace's positions, and the result seems to point to the existence 

 of some unknown, innate, and internal law which determines 

 at the same time both coloration and its transmission to 

 either or to both sexes. At the same time these authors, 

 indeed, show the harmony of natural laws and processes one 

 with another, and their mutual interaction and aid. 



It cannot be pretended that there is any evidence for 

 sexual selection except in the class of Birds. Certain of the 

 phenomena which Mr. Darwin generally attributes to such 

 selection must be due, in some other classes, to other causes, 

 and there is no ijvoof 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 gToup. Mr. 

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

 their sexual characters have been produced by such sexual 

 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, 

 therefore, 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, indeed, 

 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 some- 

 what singular reasoning to deduce from these facts the con- 



