436 HEREDITY AND ENVIRONMENT 



changed by custom and public opinion ; there 

 are also involuntary and biological causes of 

 a deep-seated' nature. Fahlenbeck has made 

 a study of 4.33 noble f amihes 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 

 age of 21 in 39 per cent., while the line ended 

 in infertile marriage in 11 per cent, and in 

 daughters only in 5 per cent. 



Broman points out that most noble families 

 of Europe die out after 100 to 250 years and 

 generally do not live beyond the third gener- 

 ation. The same is true of the families of 

 great scholars, artists and statesmen. Possi- 

 bly one cause of such declining fertility may 

 be found in too great brain activity, but there 

 is no doubt that in many instances it is due to 

 luxurious living. On the other hand bodily 

 fatigue and simple living favor fertility in 

 both animals and men. Wild animals brought 

 into captivity where they have comfortable 

 quiarters and an unwonted abundance of rich 

 food are usually infertile. And the conditions 

 of life of the upper classes of society are al- 



