?6 Heredity and Environment 



There seems to be no reason to doubt that all the extraordinary- 

 differences which organisms show, as well as all of their resem- 

 blances, 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 organ- 

 isms it is not surprising that inheritance 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 sta- 

 tistical study. He was the real founder of the scientific study of 

 inheritance ; he studied characters singly and he introduced quan- 

 titative measures. Galton'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 in- 

 tellectual capacity, artistic faculty, stature, eye color and disease. 

 As a result of his very extensive studies two main principles ap- 

 peared to be established : 



i. The Lazv of Ancestral Inheritance which he stated as fol- 

 lows: 



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 grandparents 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 + 1/16 . . . being 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 = 1/4 + 

 1/8 -f- 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 various prepotencies of sex with respect to different 

 qualities are also presumably eliminated. 



