HEREDITY AND SOCIAL FITNESS. 



A STUDY OF DIFFERENTIAL MATING IN A PENNSYLVANIA 



FAMILY. 



L INTRODUCTION. 



To the student of eugenics, as well as to those whose chief interest 

 is the practical application of its principles, there appears to be urgent 

 need of further research into the mode of inheritance of socially effective 

 traits. In this field, methods of study that handle characters in the 

 mass, without regard to the varied potentialities of the strain to which 

 the individuals belong, can avail but little. The vital questions for 

 those who seek to make eugenics a practical science will always be: 

 Given two parents of known ancestry, with reference to certain traits ; 

 how will these traits be distributed in their offspring? By what pro- 

 cess may traits that represent lower efficiency be eliminated from the 

 strain and such traits established as make for higher efficiency? The 

 laws derived from mass studies afTord no answer to these questions. 

 For their ultimate solution there is needed analysis of the types of 

 matings in families for successive generations and observation of the 

 effects of matings on the inheritance of such fundamental characteris- 

 tics as directly affect the efficiency of the individual. 



This analytical method of study has been followed with success in a 

 number of researches. We have in such histories as those of the 

 Edwards, Jukes, and Kallikak families an account of great strains of the 

 socially fit or the unfit as they have been determined by hereditary 

 causes. In the more recent studies of the Hill Folk and the Nam family, 

 published by this Office, closer analysis was made of the individual 

 and the strain to which he belonged. Evidence was given there of the 

 establishment through selected matings of pure lines of degenerates. 

 The present research has been carried along similar lines with the 

 added attempt to make a roughly quantitative estimate of certain 

 socially effective traits as their transmission was followed from gener- 

 ation to generation. 



We have here the story of two pioneer families traced through five 

 and six generations from their earliest planting on American soil. 

 An effort has been made to express the social efficiency in terms of the 

 leading traits of their members and to view their economic worth as a 

 reaction between these traits and the environment. There are no 

 eminent men and women in these famihes, no notorious criminals; 



