270 



FOUNDATIONS OF BIOLOGY 



evoked. As a result of the statistical treatment of data, 

 Galton formulated two principles of heredity which may be 

 briefly stated as follows: 



Law of Ancestral Inheritance. The two parents contribute 

 between them, on the average, one half of each inherited 



Inches 

 73 J 



72 



71 



70 



69 



68 



67 



64 



Mean height ofaU parents rjt ' 



X 



FIG. 137. Scheme illustrating Galton's law of filial regression, as shown 

 in the stature of parents and children. The circles represent the height of 

 graded groups of parents and the arrow heads show the average heights of 

 their children. The length of the arrows indicates the amount of ' regression ' 

 toward mediocrity. (From Walter.) 



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. 



Law of Filial Regression. On the average any deviation 

 of the parents from the racial type is transmitted to the 

 progeny in a diminished degree; the deviation from the racial 

 mean being two thirds as great as that of the progenitors. 

 (Fig. 137.) 



