CHAPTER XVII 



SEX REVERSALS 



IN the older literature dealing with sex-determina- 

 tion the idea is often expressed that the sex of the 

 embryo is determined by the environmental condi- 

 tion under which the embryo develops. In other words, 

 the young embryo has no sex, or is indifferent, and its 

 fate is determined by its environment. It is unnecessary 

 to go over again the evidence from which this idea origi- 

 nated, since practically all of it has been shown to be 

 defective in one way or another. 



In recent years there has been some discussion con- 

 cerning the reversal of sex, which means, by implication, 

 that a male, already determined as such, can become 

 changed into a female, and vice versa. It has even been 

 suggested that, if this can be shown to occur, the genetic 

 interpretation of sex is discredited or even overthrown. 

 It is scarcely necessary to point out that there is nothing 

 in the theory of sex as determined by sex-chromosomes 

 or genes contradictory to the idea that other influences 

 may so affect the development of the individual as to 

 change or even reverse the balance normally determined 

 by the genes. To fail to appreciate this is to fail entirely 

 in grasping the ideas that underlie the theory of the gene ; 

 for this theory postulates no more than that in a given 

 environment such and such effects are expected as a 

 result of the genes present. 



It is no more surprising that a genetic male might, in 

 an abnormal environment, turn into a female, or vice 

 versa, than that an individual might at one stage of its 



