ON THE INHERITANCE OF THE SEX-RATIO. 
By DAVID HERON, M.A. 
It has been suggested that the approach to equality in male and female births 
is an illustration in some mysterious manner of Mendel's theory of heredity. 
Observers have actually counted the number of males and females born in divers 
species with the conception that the approach to equality thus rendered manifest 
illustrates in some way Mendelian principles. I am not prepared to say it does 
not, because I have failed to grasp the manner in which those principles are 
applied to this case. If the demonstration depends, however, on the equality 
of the male and female births, their sensible inequality* in the case of man requires 
some further explanation ; it is a case wherein environment or a priori, perhaps, 
race causes permanent and fairly constant deviations from equality. The aim 
of the present paper is to show that, as far as the writer can judge, there is no 
inheritance, Mendelian or other, of the sex-ratio. So far it confirms the results of 
Dr F. A. Woods stated in the previous paper, but the method of approaching the 
problem differs from his. No assumption is made as to the existence of a Gaussian 
distribution for the frequency, and the sex-ratio for the family of each individual is 
directly calculated and tabled. The paper further deals with the case of horse as 
well as man. There is no difficulty in extending the investigations to cattle and 
dogs from the herd and studbook retui"ns, but the negative results provided by 
two such different species seem sufficient to demonstrate that the non-inheritance 
of sex is fairly widespread. 
The material is the following : 
(i) Data from a series of schedules on the size of families issued by Professor 
K. Pearson. Unfortunately this material proved less ample for this special purpose 
than we had anticipated. For although marriages must have existed at least 
15 years in both generations for a schedule to be filled in, it happened in a 
very large number of the cases that the families in both generations did not 
provide the number (four) of children which .seemed the least upon which a deter- 
mination of sex-ratio could be made. Only 348 cases were taken from this 
source. 
* See C. J. and J. N. Lewis : Natalitij and Fecundity, 1906. 
