222 



Prof. K. Pearson. 



[Mar. 19, 



At first sight this seems to indicate that for this case there is no ancestral 

 influence, where we should expect by increasing the number of DK's in the 

 grandparentage to increase the number in the offspring. But this criticism 

 is not valid, for, in the population we are dealing with, it is clear that DR is 

 the modal or mean group, and that, accordingly, it is perfectly neutral in 

 determining the regression or correlation of the gametic character. In 

 other words, the deviations of the DR ancestry from the mean population 

 gametic character are all zero and accordingly they have no weight in 

 causing the offspring to deviate from the population norm. They have, 

 in fact, no more effect on the offspring than, in the case of stature, a number 

 of mediocre ancestors have in raising or lowering the average deviation of 

 the offspring from the general population mean. 



Lastly, turning from the gametic constitution to the somatic character, 

 I have represented in the fourth and fifth columns of Table II the extent 

 to which the dominant character is present in the ancestry, and in the 

 accompanying table one sees the effect on the offspring : — 



No. of grandparents with 

 dominant character. 



Percentage of offspring with 

 dominant character. 



4 



89 



3 



78 



2 



59 



1 



33 











It will thus be obvious that, judging solely by the patent, that is the 

 somatic character of the grandparentage, there is a very marked influence 

 of the ancestry on the heritage ; that, if we select ancestry by somatic 

 character only, we shall expect an influence on the offspring varying from 

 to 90 per cent, in intensity, according to the nature of the selection. 



I think, therefore, that to deny the influence of ancestry — at any rate 

 that influence in the sense in which the biometrician uses the term — is to 

 deny the application of Mendelism to populations mating at random. 



If we start with a population in which the proportions of DD's, DR's, and 

 RR's are not those of a simple hybridisation, but given by 



p (DD) + 2q (DR) + s ( RR), 



then after the first generation of random mating the population will be 



( p + 2q + sf {p> + qf (DD) + 2 (p + q) (s + q)(p + 2q + sf (DR) 



+ (p + 2q + s) 2 (s + q) 2 (RB,), 



