BIOMETRICS 



163 



foot of the height of the mother — i.e., a mother of 5 feet high 

 would have to be reckoned as of the stature 5 feet 5 inches. 

 At first sight Galton's Law of Regression towards 

 mediocrity seems something abnormal and contrary to the 

 fact that children inherit the traits of their parents. But 

 that is due to a misunderstanding. It does not assert that 

 all the children of any given class of parents are mediocre : 

 it asserts only that on the average the children of any given 

 parents will be more mediocre than the parents themselves. 

 It must be well understood that only the average of all 

 the children of a given class is nearer to the general mean. 

 This does not exclude parents of a given class from having 

 children of different types. For instance, fathers of 

 64 inches height have, according to our correlation table, 

 sons of various heights, ranging from 62 inches up to 

 72 inches — some smaller than the fathers, some taller, some 

 of the same height ; but the average of all the sons together, 

 which works out at 66-5 inches, is nearer to P (or 69 inches) 

 than is the height of the fathers, which is 64 inches. It still 

 remains true that fathers of a greater height have on the 

 average sons of greater height than fathers of smaller 

 height. We need only compare the heights of fathers and 

 sons as given in the table (p. 157) in order to see this at 

 once. In fact, we may sum up the contents of the cor- 

 relation table, as H. M. Vernon has done, as follows. The 

 number of children of given parents is : 



All that the Law of Regression says is, that in each instance 

 the sons will on an average be nearer to the medium height, 

 as expressed by the general population, than their fathers. 



