FERTILISATION IS DECISIVE 485 



statistics in support of the theory that when the male parent 

 is the older the offspring are preponderatingly male, and that 

 when the female parent is the older the offspring are pre- 

 ponderatingly female. In short, the sex of the offspring depends 

 on the relative ages of the parents. Statistical evidence has been 

 found supporting and contradicting this theory. Schultze's 

 experiments on mice tell strongly against it. 



Yet it seems fair to notice, that if the germ-cells remain for 

 some time undetermined in regard to the sex which they will 

 express' — if, in other words, they retain for some time the poten- 

 tiality of either — there is no a priori reason against the theory 

 that the absolute and relative ages of the parents may have 

 influence. 



Or, again, even if there are two kinds of egg-cells and two kinds 

 of sperm-cells, which are from the first determined towards 

 female-production or towards male-production, the age of the 

 parent may favour the production of one kind rather than of 

 the other, or may favour the survival of one kind rather than 

 of the other. 



It is hazardous for the inexpert to draw conclusions from 

 statistics, but there seems evidence in mankind of a correlation 

 between the age of the mother and the sex of the child. The 

 younger mothers tend to have more female children ; the older 

 mothers tend to have more male children. On this the self- 

 regulating balance of sex in a nation depends. When females 

 are scarce — for instance, in a colony — they mate early, and 

 supply the demand for girls. When men are scarce — for instance, 

 after war — there are more late marriages, and therefore more boys. 



In connection with the general importance of age as a repro- 

 ductive factor, reference should be made to the remarkable work 

 of Dr. Matthews Duncan, Fecundity, Fertility, Sterility, and 

 Allied Topics (Edinburgh, 1866). 



By many authors, e.g. Girou, and at various dates, the 

 theory has been propounded that the sex of the offspring tends 



