THE STATISTICAL STUDY OF HEREDITY IN MAN 475 



ber 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 30th cousins at the present time 

 would have had a common ancestor about one thousand 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 or even Shem, Ham, 

 or Japheth, to find our common ancestor." 



Galton's data in the light of genetics. — The two main laws of Gal- 

 ton seem to us, in the light of our present knowledge of genetics, to be 

 peculiarly barren. The laws are true enough, but throw little or no 

 light upon the mechanism of heredity. They and the laws of Mendel 

 are not contradictory; in fact, each type of laws could be transmuted 

 into terms of the other. The main differences between Galton's and 

 Mendel's laws of heredity are (a) that Galton's laws do not distinguish 

 between genotypic and phenotypic differences; (6) character differ- 

 ences are often not capable of being arranged in graded series at all, 

 but are qualitatively different and without intergrades, thus being 

 unsuitable for statistical study; (c) the statistical method often loses 

 sight of the exceptional cases, which are usually the most interesting 

 and instructive. 



On the whole, it may be said that Galton's work is now considered 

 as chiefly of historical value. It served a useful purpose mainly in 

 that it definitely called attention to the fact of heredity in man, a fact 

 that was at the time hardly recognized in political, educational, and 

 sociological circles. 



