CHAPTER XXVIII 



GALTON'S LAW OF ANCESTRAL HEREDITY AND HIS 

 PRINCIPLE OF REGRESSION 



Galton (1889) was the first to recognize the distinction be- 

 tween alternative and blending inheritance. But he sought 

 nevertheless to unify the two categories of cases and finally 

 formulated in 1897 a generalized "law of ancestral heredity" 

 which he believed would include both. In seekfng such a 

 general law of heredity he had studied a representative case 

 each of blending and of alternative inheritance. The former 

 was found in family statistics of human stature, the latter in 

 the coat color of Basset hounds. The latter we should now 

 describe as a case of Mendelian inheritance involving simul- 

 taneously white spotting, and a color pattern (bi-color). 

 Stature inheritance is well described by Galton 's term, 

 "blending," but is now understood to involve multiple 

 Mendelian factors whose action is cumulative. 



In either case, Galton would have admitted that the entire 

 inheritance is from the parents through the two gametes 

 which unite to form the zygote, so that strictly speaking 

 there is no inheritance from generations more remote than 

 the parents. But he would have maintained quite correctly 

 that a better idea can be had of what the gametes on the 

 average will transmit, if one knows the character of several 

 generations of ancestors than if one knows the character of 

 the parents alone, and in this sense we may be said to inherit 

 from ancestors more remote than our parents. Galton be- 

 lieved that the apparent influence of each generation of an- 

 cestors diminished as its remoteness increased, each more 

 remote generation having only half the influence of the next 

 later one. In his own words: "The two parents contribute 

 between them, on the average, one-half, or (0.5); the four 

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

 parents, one-eighth, or (0.5)^ and so on. Thus the sum of 



246 



