SOME ASPECTS OF THE BIOLOGY OF HUMAN POPULATIONS 543 



to suppose that the relative fertihties of the most fertile por- 

 tions of the populations in the several main occupational 

 classes, as given by these data, are not safely comparable. 



Public Service 



Manufacturing 

 Agriculture 



Extraction of Minerals 

 J I I I I I I I ' 



0J2 0.4 0.6 0.8 1.0 iJi lA 1.6 1.8 ;i.o 

 Relative Size of Family 



Fig. 9. Bar diagram showing relative average size of family experienced by 

 mothers of 1923 in their reproductive lives up to that date, according to 

 occupation of fathers who were, in 1923, forty-five years of age or over. 



The only essential difficulty with the figures is that the uni- 

 verse of discourse which they encompass is a definitely 

 limited one, and we cannot safely generalize beyond these 

 bounds. 



