24 HEREDITY AND SOCIETY 



the Scott brothers, the Thurlow brothers, the two 

 Wordsworth groups and the two pairs of Wesley 

 brothers. It seems clear that in the second and third 

 groups we have usually to consider persons who are 

 exceptions to their social surroundings and naturally 

 belong to the classes where the satisfactory perform- 

 ance of daily duties rarely brings with it any public 

 notice. 



This aspect of our subject leads us to inquire into 

 the sociological meaning of the groups of men of 

 differing types and professions which we recognize in 

 our midst. Owing to the localized geographical dis- 

 tribution of the various branches of industry through- 

 out the country, we have probably whole classes of 

 persons, more or less distinct from each other in 

 physical and mental qualifications, where marked ad- 

 ministrative, commercial, industrial or technical ability 

 have been segregated, and exist, duly graded, from top 

 to bottom of the group. 



This differentiation of type, as an essential concomi- 

 tant of civilization, is probably the origin of the class 

 distinctions which exist among us, and which, sometimes 

 crystallizing out into a " caste " system, have existed as 

 far as we can tell in every civilization. It is evident 

 that a much higher and more certain proportion of 

 ability of any required sort can be obtained through 

 persistent social association, with its corollary of like- 

 to-like mating, rather than by any chance system of 

 general settlement and mingled intermarriage. 



Very little work has yet been undertaken to throw 

 light on the sociological principles which underlie these 

 questions, but all the evidence available goes to show 



