THE FACTORS WHICH DETERMINE SEX 649 



slight evidence that the percentage of female births is a little 

 higher among those classes which are best nourished or subject 

 to more favourable circumstances, but the differences are very 

 small. 



Punnett * has examined the statistics collected in the official 

 census of the county of London for the year 1901, with a view 

 to determining the relative proportions of the sexes amongst 

 different classes of society. The following is his summary and 

 conclusion : 



" If the population of London be divided into three portions 

 exhibiting graduated poverty, it is found that the proportion of 

 male to female infants produced [or rather which have sur- 

 vived] is lowest in the poorest portion, highest in the wealthiest 

 portion, and intermediate in the intermediate portion. The 

 proportion of males is highest of all in a number of births taken 

 from Burke 's Peerage, where the nutrition may be supposed to 

 be of the best. From this alternative conclusions may be 

 drawn : that either more favourable conditions of nutrition 

 (1) may result in a large proportion of male births [a conclusion 

 which is contrary to that indicated in the returns mentioned 

 above, but which nevertheless appears to be warranted at first 

 sight], or (2) may have no effect on the proportion of the sexes, 

 or (3) may even result in a relative preponderance of female 

 births, but that in the last two cases the effect is masked by 

 other factors which affect unequally the different strata of 

 society. Such factors are shown to exist in a differential infant 

 mortality, a differential birth-rate, and probably also in a 

 differential marriage-age. These factors all tend to diminish 

 the proportion of males in the poorer portions of the population, 

 and consequently render the first of the above alternative con- 

 clusions improbable. Whether the second or third of the other 

 possible conclusions is to be accepted must remain doubtful so 

 long as we are not in a position to estimate the quantitative 

 effect of the factors given above. From the necessarily rough 

 estimate which he has been able to form, the writer's opinion is 

 that their combined effect would not be sufficiently great to 

 mask a preponderance of female births due to better nutrition, 



1 Punnett, " On Nutrition and Sex-Determination in Man," Proc. Camb. 

 Phil. Soc., voL xii., 1903. 



