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 dealing 
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 
