HEREDITY 



527 



to enable us to predict what, on the average, should be the 

 product of this selected ancestry. 



Inheritance complex. The heritage from the parent is not 

 therefore a simple thing, but rather a complex stream, or, more 

 properly, two streams that meet from different directions, each 

 made up of currents contributed from many tributaries. How 

 much now has each tributary (ancestor) contributed to the 

 general and composite mixture that we call the heritage ? 



Galton l made the first attempt to answer this question, and 

 announced as the law of ancestral heredity that the two immedi- 

 ate parents contributed between them one half (0.5) of the 

 effective heritage, the grandparents one fourth (o.5) 2 , the great- 

 grandparents one eighth (o.5) 3 , and so on, so that the effective 

 contributions of the successive generations would be represented 

 by the fractions \, \, \, -jL, etc., and the total heritage would 

 be represented by the sum of these fractions, which, extended 

 to infinity, would equal I, thus accounting for the total heritage. 



This general law applies to generations, not to individual 

 ancestors, and these fractions should be still again divided by the 

 number of ancestors in each generation in order to determine 

 the fractional share contributed by each individual ancestor. 

 The following table exhibits the fractional contribution of each 

 generation and of each individual ancestor according to the law 

 of ancestral heredity as stated by Galton. 



EFFECTIVE HERITAGE CONTRIBUTED BY EACH GENERATION AND BY 



EACH SEPARATE ANCESTOR ACCORDING TO THE LAW OF 



ANCESTRAL HEREDITY AS STATED BY GALTON 



1 Galton, Natural Inheritance, pp. 134-137 ; Proceedings of the Royal Society, 

 LXI, 402. 



