78 Heredity and Environment 



owing to the intermarriage of cousins of various degrees the 

 actual number of ancestors is much smaller than the theoretical 

 number. For example, Plate says that the late Emperor of Ger- 

 many had only 162 ancestors in the loth ascending generation, 

 instead of 512, the theoretical number. Nevertheless this calcu- 

 lation will serve to show how widespread our ancestral lines are, 

 and how nearly related are all people of the same race. 



Davenport concludes that no people of English descent are 

 more distantly related than 3Oth cousins, while most people are 

 much more closely related than that. If we allow three genera- 

 tions to a century, and calculate that the degree of cousinship is 

 determined by the number of generations less two, since first 

 cousins appear only in the third generation, the first being that 

 of the parents and the second that of the sons and daughters, we 

 find that 3Oth cousins at the present time would have had a com- 

 mon ancestor about one thousand years ago or approximately at 

 the time of William the Conqueror. As a matter of fact most per- 

 sons 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 Law of Filial Regression is the second principle which 

 Galton deduced from his statistical studies, or it may be called 

 the tendency to mediocrity. He found that, on the average, ex- 

 treme peculiarities 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 good fortune if he begets a son who is as richly en- 

 dowed as himself." This so-called law of filial regression is 

 represented graphically in Fig. 25 in which the actual stature of 

 individual parents is shown by the oblique line, the stature of 

 children by the dotted curve, and the mean stature of the race in 

 the horizontal dotted line. 



