72 PRODUCTION OF NATIONALITY 



frequently marry at home, bring up their famiHes at 

 home and after a time return themselves. Germany 

 must have lost permanently some part of the most 

 valuable element in her stock, leaving the residuum 

 a little more docile, with fewer windows open to the 

 fresh air of the great world. 



The same conscious preferences act negatively. 

 Military nations do not attract and would not for 

 long retain immigrants of other dispositions. How 

 far and to what extent the actual stock is being 

 modified in different countries, I cannot judge, and 

 I do not know of exact work bearing on the subject. 

 Theoretically, at least, we must suppose processes 

 of internal selection to be active in the different 

 isolated areas. All marriages are not fertile nor 

 fertile to the same degree. The percentage of chil- 

 dren produced from a given number of nubile 

 persons differs in countries according to factors 

 depending on the national character and environ- 

 ment. Prudential restraint upon marriage obviously 

 differs from country to country according to the 

 social, political and economic conditions that favour 

 or impede early marriages in rural or urban popula- 

 tion, or in one class or the other. A hundred nubile 

 couples in one environment might have the same 

 percentage of children as the same hundred in another 

 environment, but the incidence of the fertility would 

 almost certainly differ ; precisely the same couples 

 would not marry in the two cases. Actually we should 

 expect that not only the incidence of fertility, but 

 the actual percentage fertility would differ, especially 

 if we take into consideration the habit of setting 

 deliberate limits to fertility. Many able writers have 



