232 HEREDITY AND SEX 



wide of the mark if we attempt to draw conclusions 

 concerning the determination of sex itself from devia- 

 tions such as these in the sex ratio, yet it is the mistake 

 that has been made over and over again. We must 

 look to other methods to give us sufficient evidence as 

 to sex-determination. Fortunately we are now in a 

 position to point to this other evidence with some 

 assurance. With the mechanism itself worked out, 

 we are in a better position to explain slight variations 

 or variables that modify the combinations in this way 

 or in that. 



THE ABANDONED VIEW THAT EXTERNAL CONDITIONS 

 DETERMINE SEX 



But before taking up the evidence for sex-determina- 

 tion in man I must briefly consider what I have been 

 bold enough to call the abandoned view that external 

 conditions determine sex. 



Let us dismiss at once many of the guesses that have 

 been made. Drelincourt recorded 262 such guesses, 

 and Geddes and Thomson think that this number has 

 since been doubled. Naturally we cannot consider 

 them all, and must confine ourselves to a few that 

 seem to have some basis in fact or experiment. 



The supposed influence of food has been utilized in 

 a large number of theories. The early casual evidence 

 of Landois, of Mrs. Treat, and of Gentry has 

 been entirely set aside by the careful observations of 

 Riley, Kellogg and Bell, and Cu6not. In the latter 

 cases the experiments were carried through two or even 

 three generations, and no evidence of any influence of 

 nourishment was found. 



