244 Studies in Animal Behavior 



its value in the mating of the lower vertebrates the 

 voice might never have been evolved and man never 

 have become man. 



While the specialization of senses, which, in cer- 

 tain cases at least, has been carried on mainly for 

 sexual purposes, naturally afforded a basis for the 

 elaboration of many instincts, it is practically im- 

 possible to trace in detail how various instincts, sex- 

 ual and other, may have acted and reacted on one 

 another's development. But we can discern enough 

 of the influence of sex differentiation on the evolu- 

 tion of behavior to feel assured of its importance. 

 The necessity of solving the one problem that con- 

 fronts all dioecious animals which do not simply shed 

 their sexual products at random into the water has 

 kept behavior in one sphere up to a certain mini- 

 mum standard. The male must find and impregnate 

 the female, and this fact sets a certain limit to his 

 degeneration, at least in some period of his life. 

 But besides acting as a check to degeneration, the 

 necessity for mating has, in general, been a con- 

 stant force making for the evolution of activity, en- 

 terprise, acuity of sense, prowess in battle, and the 

 higher psychic powers. We cannot pretend accu- 

 rately to gauge its role in the evolution of mind, but 

 it has evidently been a factor of enormous potency. 



