THE LAW OF ANCESTRAL HEREDITY 105 



physical characters both in men and in other animals. 

 Assuming and the assumption seems to be a reasonable 

 one that equal fraternal correlations indicate the exist- 

 ence of equal correlations between parents and children, 

 we arrive at the conclusion that the resemblance 

 between parents and their offspring is of much the 

 same kind and amount in the case of mental as it is in 

 the case of bodily characteristics. 



What we may perhaps describe as the main general- 

 ization so far arrived at by biometricians is known 

 as the Law of Ancestral Heredity. This hypothesis 

 supposes, or at least in its original form supposed, that 

 every ancestor of a particular individual contributes 

 its quota to the heritable qualities displayed by that 

 individual. The law also states that the average 

 amount of resemblance between an individual and any 

 particular ancestor is capable of definite numerical 

 expression. Thus the mean amount of correlation 

 between (i) the two parents and the offspring, (2) the 

 four grandparents and the offspring, (3) the eight 

 great-grandparents and the offspring, and so on, is 

 believed to diminish in a geometrical series, which is 

 the same for all organisms and for all characters. The 

 actual amounts of these correlations were expressed by 

 Galton in the form of the series 0-50, 0-25, 0-125, etc. 

 Pearson regards them as being more nearly represented 

 by the more rapidly diminishing series 0-6244, 0-1988, 

 0-0630, etc. 



Now, there can be no doubt that the law as stated 

 above has been disproved in specific instances, and was 

 indeed disproved by the work of Gregor Mendel before 



