98 Heredity. 



ing effect of external influences, but to the natural selec- 

 tion of congenital variations. 



The fact that our theory requires us to believe that the 

 egg of one of the higher animals is complex beyond our 

 powers of conception, must not be regarded as an argu- 

 ment against the theory, for we are compelled to believe 

 this in any case. The difference between our theory 

 and other attempts to explain the phenomena of heredi- 

 ty, is that it does what no other hypothesis attempts. 

 It furnishes a simple explanation of the manner in which 

 the ovum has acquired its present complexity. 



In the following chapters I shall give some of the 

 reasons for believing that the difference between the 

 functions of the sexual elements which the theory re- 

 quires does actually exist, but even in the absence of this 

 proof it would be natural to conclude that if race modi- 

 fication could be furthered and aided by the divergent 

 specialization of the functions of the two reproductive 

 elements, natural selection would, in all probability, have 

 acted so as to bring such a specialization about. 



We know that the influence of natural selection is 

 constantly exerted to seize upon and perpetuate any ten- 

 dency to division of labor among the organs and tissues 

 and cells of the body, and it is only natural that the 

 successive stages in the specialization of the sexual 

 elements should have been perpetuated like any other 

 useful specialization. 



