518 INHERITANCE OF MENTAL TRAITS 



The Law of Filial Regression. — From Table 1 it 

 will be seen that superior parents tend to have children 

 who are also superior, but less superior than themselves; 

 and that inferior parents tend to have children who are 

 inferior, but less so than themselves. This illustrates the 

 " law of filial regression, " which was first formulated 

 by Francis Galton. It is merely a statement of the fact 

 that the offspring of parents who are exceptional in a 

 particular trait tend to be less exceptional in that trait 

 than their parents. The law holds for complex traits 

 like height or intelligence, but not for simple traits like 

 eye-pigment, color-blindness, etc. 



Mental Resemblance of Twins. — Both in physical 

 and mental traits a much higher coefficient of resem- 

 blance has been found for twin-pairs than for ordinary 

 sibs, namely .70 to .90 for twins as compared with .50 

 for sibs. Twins, however, are believed to be of two kinds, 

 those originating from two eggs separately fertilized and 



