THE METHOD OF BIOMETRY 



459 



from them because of the influence of more remote ancestors. The 

 law of Filial Regression is an expression of the fact that in any 

 large group, in which considerable variation occurs, the offspring 

 tend to be hke the average and not like the extremes of the parent 

 generation. In other words, the offspring of average parents are 

 average ; those of parents below the average are below the average ; 

 those of parents above the average are above the average; but the 



Fig. 239. — Diagram illustrating Galton's law of Filial Fiegression. The circles 

 represent the height class to which the parents belong, while the arrow points 

 indicate the average height of their respective offspring. The children of 

 parents that are either below or above the average are nearer the average 



than were the parents. 



(From Walter, "Genetics," copyright, 1922, by The MacmiUan Co., reprinted by 

 permission.) 



offspring of parents that are either below or above the average are 

 nearer the average than were the parents (Fig. 239). The original 

 study of Galton on human height has been supplemented by inves- 

 tigations of inheritance of eye-color, mental ability, length of life, 

 and other characteristics by Karl Pearson, Raymond Pearl, and 

 other biometricians of to-day. 



Pure Lines and Selection. — Galton's observations were made 

 on groups that were not subjected to experimental control. His 



