88 CONTROLLED NATURAL SELECTION 



Finally, it will be well to classify secondary 

 sexual characters in the light of this new 

 theory. 



MONO-SEXUAL CHARACTERS : 



1. Characters that are adaptations to a mono- 

 sexual environment ; for instance, associated 

 with a food supply confined to one sex, with 

 copulation, with the rearing of young, with 

 the recognition or finding of one sex by the 

 other, &c. 



2. Characters whose purpose is to control 

 Natural Selection within the pair, value marks; 

 for instance, attracting colour, sound, scent, 

 &c. confined to the male. 



It must be clearly understood that the second 

 cause of mono-sexual characters is, like the 

 first, an environmental character. It is the 

 result of selection by enemies, which selec- 

 tion has been shown to be one of the most 

 important factors of a species' specific en- 

 vironment. For this reason it should not, 

 theoretically, be given a major heading in 

 the classification of the causes of mono-sexual 

 characters. There is, however, a side issue 

 which to some extent justifies this arrange- 

 ment ; for the species behaves towards enemies 

 in a particular manner. 



It adjusts this selection by enemies so that, 



