i66 THE FIRST PRINCIPLES OF HEREDITY 



of given individuals and their fertility. For instance, he 

 found by biometrical calculations for man that tall women 

 procreate faster than small women, also that dark-eyed 

 people are more fertile than light-eyed. This would 

 naturally lead to a gradual modification of the race into 

 the direction of the more prolific tj^pe. " Genetic Selec- 

 tion," as this process has been called, is then, we see, an 

 active force in producing a progressive change of type, 

 and must, if there is differential fertility between various 

 types, lead to a differentiation of such types. But, further, 

 that fertility really varies Pearson was able to demonstrate 

 in various cases. Thus he found, e.g., that of 176 Shirley 

 poppies, with 4,443 capsules, arranged in the following 

 array. 



Bands /5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 

 Frequency i 11 32 56 148 363 628 925 954 709 397 iS5 5^ 12 i 



the poppies with twelve and thirteen stigmatic bands — i.e., 

 those with the greatest frequency — were the most fertile ; 

 those with eleven and fourteen bands w^ere less fertile, and 

 those with the extreme number of bands on either side 

 had practically no seeds at all. " Fertility is, then," 

 according to Pearson, " not only uniformly distributed 

 among all individuals, but for stable races there is a strong 

 tendency for the character of maximum fertility to become 

 one with the character which is the type " (i.e., that of the 

 greatest frequency). In a new environment a change of 

 the old centre of fertility may take place, and other types 

 of character previously less fertile may now become more 

 fertile. 



There is one more point to be mentioned in connection 

 with these problems, which we have only lightly touched 

 upon. The modification of the character of the race in a 

 given direction can take place only if the fertility of a 

 given type of individuals is inherited — i.e., if all the 

 successive generations of that type exhibit the same 



