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THE POPULAR SCIENCE MONTHLY 



ferences which organisms show, as well as all of their resemblances, are 

 due to differences or resemblances in the hereditary and environmental 

 factors which have been operative in their development. But in view 

 of this universal variability of organisms it is not surprising that in- 

 heritance has seemed capricious and uncertain — " a sort of maze in which 

 science loses itself." 



B. STATISTICAL STUDY OF INHERITANCE 



Francis Galton was one of the first who attempted to reduce the 

 mass of conflicting observations on heredity and variation to some 

 system and to establish certain principles as a result of statistical study. 

 He was the real founder of the scientific study of inheritance, he cre- 

 ated characters singly and he introduced quantitative measures. Gal- 

 ton's researches, which were published in several volumes, consisted 

 chiefly in a study of certain families with regard to several selected 

 traits, viz., genius or marked intellectual capacity, artistic faculty, stat- 

 ure, eye color and disease. As a result of his very extensive studies two 

 main principles appeared to be established : 



1. The Law of Ancestral Inheritance which he stated as follows: 



The two parents contribute between them on the average one half of each 

 inherited faculty, each of them contributing one quarter of it. The four grand- 

 parents contribute between them one quarter, or each of them one sixteenth; and 

 so on, the sum of the series 1/2 + 1/4 +'1/8 -f- 1/16 . . . beting equal to 1, as 

 it should be. It is a property of this infinite series that each term is equal to the 

 sum of all those that follow: thus 1/2 = 1/8 + 1/16 +'...,1/4 = 1/8 + 1/16 + 

 . . ., and so on. The prepotencies of particular ancestors in any given pedigree 

 are eliminated by a law which deals only with average contributions, and the vari- 

 ous prepotencies of sex with respect to different qualities are also presumably 

 eliminated. 



Parents 



Grand Pts 



Gt G'd Pts 

 Gt G\ Gd Pts 



Fig. 48. Scheme to Illustrate Galton's " Law of Filial Regression " as 

 Shown in the Stature of Parents and Children. The mean height of all parents 

 is shown by the dotted line between 68 and 69 inches. The circles through which 

 the diagonal line runs represent the heights of graded groups of parents and the 

 arrow heads indicate the average heights of their children. The offspring of under- 

 sized parents are taller and of oversized parents are shorter than their respective 

 parents. (From Walter.) 



