' CONTROL OF HEREDITY: EUGENICS 451 



In Massachusetts the birth rate of the foreign 

 born is twice that of the native population while 

 the death rate is about the same for both. The 

 same is true of the older families in many parts 

 of the world. 



Professor Cattell has recently made a sta- 

 tistical study of the families of 917 Ameri- 

 can men of science and he finds that the 

 average size of family of the parents of these 

 men was 4.66 children, whereas the average 

 size of family of these men is 2.22 children. 

 In one generation the fertility of these lines 

 has been reduced by more than half. The 

 causes of this decline are chiefly voluntary 

 being assigned to health, expense and other 

 causes. 



But the causes of sterility are not only so- 

 cial and voluntary ones, which could be 

 changed by custom and public opinion; there 

 are also involuntary and biological causes of 

 a deep-seated nature. Fahlenbeck has made 

 a study of 433 noble families of Sweden which 

 have become extinct in the male line, and he 

 shows that the last male died unmarried in 

 45 per cent, of these families, and before the 



