224 HEREDITY AND ENVIRONMENT 



the number of generations less two, since first 

 cousins appear only in the third generation, 

 the first being that of the parents and the sec- 

 ond that of the sons and daughters, we find 

 that 30th cousins at the present time would 

 have had a common ancestor about one thou- 

 sand years ago or approximately at the time 

 of William the Conqueror. As a matter of 

 fact most persons of the same race are much 

 more closely related than this, and certainly 

 we need not go back to Adam nor even to 

 Shem, Ham, or Japheth to find our common 

 ancestor. 



2. The second principle which Galton de- 

 duced from his statistical studies is known as 

 the Law of Filial Regression, or what might 

 be called the tendency to mediocrity. He 

 found that, on the average, extreme peculiari- 

 ties of parents were less extreme in children. 

 Thus, "the stature of adult offspring must on 

 the whole be more mediocre than the stature of 

 their parents, that is to say more near to the 

 mean or mid of the general population"; and 

 again, "the more bountifully a parent is 

 gifted by nature, the more rare will be his 



