PURPOSE OF SONG 149 



be left without their complement of pairs just 

 because this male mistook the voice Of that, 

 and avoided it when there was no necessity for 

 doing so. So that just as from the point of 

 view of " recognition " each female must be able 

 to distinguish the voice of its own kind, so 

 likewise the warning can only be adequate 

 providing that the sounds are specifically distinct. 

 A point, however, arises here in regard to 

 closely related forms. Some species require 

 similar food and live under similar conditions of 

 existence ; they meet in competition and fight 

 with one another ; and, if they did not do so, the 

 food-supply of a given area would be inadequate 

 to support the oiFspring of all the pairs inhabiting 

 that area. Generally speaking, the more closely 

 related the forms happen to be, the more severe 

 the competition tends to become ; and it may be 

 argued that in such cases a similar song would 

 contribute to more effective distribution and in 

 some measure provide against the necessity of 

 physical encounter ; that, in fact, it would stand 

 in like relation to the success of all the 

 individuals concerned, as does the song to the 

 individuals of the same species. But we must 

 bear in mind that the primary purpose of song 

 is to direct the females to those males that 

 are in a position to breed ; and to risk the 

 possibility of prompt recognition in order that 

 the males of closely related species should fight 

 the less, would be to sacrifice that which is 

 indispensable for a more remote and less 

 important advantage. 



