l(j STATISTICS OF SEX 



list had a miix-Mia] tendency, or if, in the great majority of cases, this 

 tendency \\ as exceedingly small, the effect would not be shown. 



As to this latter case, the fact of any unisexual tendency, however 

 minute, would be of great scientific interest, but of no practical im- 

 portance. It would hardly be worth while for any parent or any com- 

 munity to lay great stress on any cause which would result only in 

 increasing the chances of male or female offspring by 3 or 4 per cent. 

 It seems highly improbable that any very rare or highly artificial cause 

 would produce a unisexual tendency, if no ordinary cause produced it. 

 The absence of any strongly marked unisexual tendency in the families 

 .we have examined, therefore, justifies us in concluding, at least with 

 a high degree of probability, that the causes of sex are beyond artificial 

 control. 



5. THE UNISEXUAL TENDENCY IN MULTIPLE BIRTHS. 



We have next to consider a sort of family in which the conditions are 

 peculiarly favorable for drawing conclusions on the general question of 

 the cause of sex. These are families consisting of children of a single 

 birth in twins or triplets. Considering first the case of twins, we begin 

 with the effects which would result on two extreme hypotheses as to the 

 cause of sex. 



HYPOTHESIS I. Tlie distinction of male and female exists in original 

 germs, antecedent to conception, presumably supplied by the father. 



In this case we should find the same random distribution of twin chil- 

 dren between the two sexes that we find to exist in families of two. In 

 four births of twins we should have one of two males, one of two females, 

 and two bisexual. Only in two ways could this conclusion be avoided. 

 One is by supposing that a germ of either sex is more likely than not to 

 have one of the same sex in physical juxtaposition with it. This view 

 seenis inadmissible because, even if such juxtaposition did exist in any 

 case at any moment, it would not be permanent. The other supposition 

 is that at certain periods there is an abnormal excess of male germs and 

 at other periods a similar excess of female germs in the same father. In 

 the absence of permanent unisexualism on the part of any one father, 

 which was shown in the preceding section, such an inequality can not 

 be permanent. It therefore seems to me that this supposition is also 

 too artificial and unlikely to be considered. We may therefore consider 

 the statistical distribution of twin children between the sexes to afford a 

 test of the above hypothesis. 



