492 HEREDITY AND SEX 



offspring of one sex rather than of the other ? Is the relative 

 age of the two parents of any importance ? Does the health 

 and vigour of the parent matter ? 



Age of Parents. — Hofacker (1823) and Sadler (1830) inde- 

 pendently published statistics referring to about two thousand 

 births, which favoured the conclusion that when the male parent 

 is the older the offspring are preponderatingly male, and vice 

 versa ; but this has not been confirmed, far less established, and 

 the experiments of Schultze tell strongly against its validity. 



At the same time, if the gametes are for a while indifferent 

 or unbiassed in regard to the sex which they will express, or if 

 there is a selective process which decides whether the gametes 

 determined towards femaleness or those determined towards 

 maleness will survive, it may be that the absolute and relative 

 ages of the parents are not without influence. 



Comparative Vigour. — A widespread idea among breeders is 

 that the sex of the offspring tends to be that of the more vigorous 

 parent. But when we try to analyse the concept of comparative 

 vigour, we find ourselves knee-deep in vagueness. Nor do the 

 facts bear out the conclusion. Thus it is usually said that con- 

 sumptive mothers produce a great excess of daughters, whereas 

 the theory of the influence of comparative vigour, as stated by 

 Girou and others, would lead us to expect the opposite. 



According to Starkweather, " sex is determined by the superior 

 parent, and the superior parent produces the opposite sex"; 

 but the concept of " superiority " is even more vague and useless 

 than that of greater vigour. Van Lint has tried to rehabihtate 

 this theory, maintaining that when the spermatozoon is stronger 

 than the ovum, the result is a female, and conversely. There 

 does not seem to be any basis for this view. 



An interesting question, which deserves further inquiry, is 

 whether a prepotent sire has, along with his tendency to transmit 

 his somatic qualities, a tendency to bias the offspring towards his 

 own sex, or towards femaleness ; or, more generally, whether 



