26 SEXUAL DIMORPHISM 



Another objection of Mr. Wallace's is that each bird finds 

 a mate under all circumstances ; in other words, that failure 

 to please one female does not imply failure to please all. 

 But, nevertheless, it would seem probable, especially in 

 polygamous animals, that some males are fathers on a much 

 larger scale than others. 



Again, he considers it very improbable that through 

 thousands of generations all the females of a species should 

 always have had the same taste with regard to every detail 

 in the nuptial adornment of their mates. This is certainly a 

 valid objection, or at least appears to be so. The criticism 

 of Mr. Romanes is that it is not very safe to infer what 

 sentiments may be in the mind of a hen. We have evidence 

 that the preferences of females with regard to male attrac- 

 tions are very conservative in our own species, but it is 

 certainly difficult to conceive that the female Argus pheasant 

 should have the power or the opportunity of appreciating 

 minute differences in the perfection of the ocelli on the 

 wing-feathers of the male. 



Mr. Wallace argues that the principal cause of the greater 

 brilliancy of male animals in general, and of male birds in 

 particular, is, that they do not stand so much in need of 

 protection by concealment as the females do. Therefore 

 natural selection is more active in repressing in the female 

 those bright colours which are normally produced in both 

 sexes by general laws. More than this, natural selection 

 promotes the development of heightened colour in the males, 

 because this is correlated with health and vigour, and the 

 healthy and vigorous males are preserved by natural 

 selection. 



With regard to the display which, according to Mr. 

 Romanes, is the strongest of all Mr. Darwin's arguments in 

 favour of sexual selection, Mr. Wallace says that there is no 

 evidence that the females are in any way affected by it. On 



