Social Environment and Eugenics 95 



ured, A glance at the tables will show that 

 density of population and other environmental 

 factors are measured at approximately the 

 average date of birth of the noted men, and 

 that the measurement so taken is regarded 

 as indicative of the formative environment 

 through the years of immaturity. It might be 

 questioned whether this procedure is allowable 

 in view of the shifting population of the United 

 States, and the rapidly changing conditions. It 

 is therefore necessary to ascertain the relevant 

 facts. 



The number of persons who grow up in the 

 locality in which they are born is much larger 

 than is popularly supposed. Recent censuses 

 (1870-19 10) find only from twenty to twenty- 

 four per cent of the native population outside 

 of the state of birth. Of course a part of those 

 remaining are children, some of whom will 

 move before maturity; yet not a large propor- 

 tion, since migrants are more likely to be adults 

 than children.^ It is therefore safe to assume 

 that from one-half to three-quarters of the pop- 

 ulation grow up in the same state in which they 

 are born. Of those who move, a good part do 



1 For the case as to foreign immigrants see Abstract of 

 Thirteenth Census of the United States, pp. 124-125. 



