10 STATISTICS OF SEX 



child, tin- .">< males will be followed by 18 males and 12 females. The 20 

 females will be followed by 12 males and 8 females. 



The numbers will be the same for Class B, only substituting female 

 for male preponderance. Thus the total outcome will be: 



Class A Class B Total 



2 males 18 8 26 



Male-female 12 12 24 



Female-male 12 12 24 



2 females 8 18 26 



That is, in 100 families of 2 children each, we shall have 52 with 

 children of one sex, and 48 with children of different sexes, instead of 

 50 of each class. 



The result will be yet more decisive when Ave consider families of a 

 greater number of children. Whatever the number of the family, the 

 theory of probabilities and combinations gives a certain distribution of 

 male and female children, which would be the most likely result of pure 

 chance. For example, in families of 3, the most likely chance distri- 

 bution would be three cases in which the children were of different 

 sexes for one in which all three were of the same sex. But, were 

 there any tendency among special parents to a production of chil- 

 dren of one sex, the proportion of families in which all three were of 

 the same sex would be greater than that given by the law of chance 

 distribution. To show the preponderance, let us suppose the tendency 

 to be the same as in the preceding example, and the number of families 

 of 3 children each to be 500, or 250 of each class. The result will be : 



Class A Class B Total 



3 males 54 16 70 



2 males, 1 female 108 72 180 



1 female, 2 males 72 108 180 



3 females 16 54 70 



Assuming no unisexual tendency on the part of parents, the probable 

 result would be a proportion of three families not all of the same sex 

 to one of the same sex. The results would then compare thus: 



Families Actual Probable 



3 children of 1 sex 140 125 



3 children of 2 sexes 360 375 



The result is an excess of 15 unisexual families. 



Let us now pass on to the general problem of which the preceding exam- 

 ples are special cases. We have cited the well-known fact of a general or 

 average unisexual tendency in the male direction among parents of the 

 Semitic race. The question before us is whether this tendency of this race 

 is the same among all parents. What we know to start with is that, if 

 some parents have a tendency greater than the normal to produce male 

 children, then there must be a corresponding tendency among other 



