Heredity and Sex 79 



If, as has been suggested, the determination of sex in 

 general depends upon the inheritance of a Mendelian factor 

 differentiating the sexes, it is highly improbable that the 

 breeder will ever be able to control sex. Male and female 

 zygotes should forever continue to be produced in approxi- 

 mate equality, and consistent inequality of male and 

 female births could result only from greater mortality on 

 the part of one sort of zygote than of the other. Only in 

 parthenogenesis can man at will control sex, and until he 

 can produce artificial parthenogenesis in the higher animals, 

 he can scarcely hope to control sex in such animals. 



Negative as are the results of our study of sex control, 

 they are perhaps not wholly without practical value. It is 

 something to know our limitations. We may thus save 

 time from useless attempts at controlling what is uncon- 

 trollable and devote it to more profitable employments. 



