NIloIJTKK ARTICLES AND DISC VSSlON 



ON THE INHERITANCE OF TRICOLOR COAT IN 

 GUINEA-FIGS, AND ITS RELATION TO GAL- 

 TON'S LAW OF ANCESTRAL HEREDITY 1 



In 1889 the late Francis Galton formulated a "law of ancestral 

 heredity" which he believed would prove to be of general 

 applicability in as much as he had already applied it with 

 gratifying results to two widely different categories of cases, viz.. 

 the height of man and the color of dogs. The law as stated by 

 Galton is : 



The two parents contribute between them, on the average one-half, 

 or (0.5) of the total heritage of the offspring; the four grandparents, 

 one-quarter, or (0.5) 2 ; the eight great-grandparents, one-eighth, or 

 (0.5) 3 , and so on. 



The validity of Galton 's law has since been seriously called in 

 question, though neither of his two eases has yet received a 

 wholly satisfactory explanation, but sufficient progress has been 

 made in the study of heredity to show the unsoundness of the 

 basic principle on which Galton 's generalization rested. In 

 reality there is no such thing as "ancestral" inheritance; for we 

 inherit from our parents only, not from our more remote an- 

 cestors. It is true that a knowledge of the more remote ancestry 

 may help us to understand better what we have inherited from 

 our parents, but it is clear that such knowledge of the ancestors 

 will not enable us to predict the character of their descendants in 

 the precise manner outlined by Galton. In a specific case, the 

 inheritance of albinism in mice, I made in 1903 a test of the 

 comparative value of Galton 's law and Mendel's law in predict- 

 ing the character of offspring, with the result that Mendel's law 

 gave predictions closely according with observation, whereas 

 predictions based on Galton 's law proved wholly unreliable. 



As regards height, however, and other size characters. Gal- 

 ton's law is quite as good a basis for predicting the result of 

 particular matings as is Mendel's. Indeed it is not clear that 

 either of them is applicable to such cases as human stature. 



