22 THE TREND OF THE RACE 



aptitudes, disposition and character as they are in their form and 

 features. 



The extent to which our human differences are hereditary 

 is a matter about which there is much difference of opinion. Con- 

 cerning the peculiarities of features and complexion which are 

 characteristic of racial subdivisions and which may be seen very 

 frequently to run in members of a family there is little oppor- 

 tunity for disagreement. Stature, strength, endurance, eyesight 

 and temperament, since they are obviously influenced by the 

 environment are frequently considered as affected more by the 

 environment than through variations in hereditary constitution. 

 We cannot test the matter experimentally as we might in deaHng 

 with characters of corn or wheat, but it is possible to investigate 

 the subject by statistical methods. Professor Karl Pearson and 

 several of his associates of the Galton Laboratory of the Univer- 

 sity of London have tested the relative influence of heredity and 

 environment in a number of human traits such as eyesight, height, 

 weight and intelligence. Their method is to ascertain the degree 

 of similarity existing between certain characteristics occurring in 

 parent and offspring and among the siblings of the same family. 

 These similarities may be expressed numerically by a coefficient 

 of correlation. Coefficients of correlation were worked out also 

 for various environmental differences. These correlations if based 

 on a sufficient number of cases will afford a measure of the in- 

 fluence exerted by the environment. Then the correlations 

 between relatives may be compared with those correlations which 

 are the result of environmental influence. In the study of the 

 relative influence of heredity and environment on defects of vision 

 Barrington and Pearson ascertained that the coefficient of corre- 

 lation between parent and offspring and between siblings for 

 keenness of vision was from .4 to .6 which is much the same value 

 as that which is found for other hereditary traits. They measured 

 the correlations of keenness of vision and refraction with environ- 

 mental conditions in a large number of school children living 

 under a variety of circumstances, and found that these correla- 

 tions were very small. In other words, the eyesight of children 



