STATISTICAL AND PHYSIOLOGICAL LAWS 331 



distribution of hereditary qualities, not physiological general- 

 isations in regard to individuals. There is no mysterious force 

 of filial regression, causing offspring to gravitate towards 

 mediocrity. There is a statistically observed tendency to keep 

 up an average in a stock, and the explanation offered of the 

 fact is that each offspring has a multiple ancestry, and that 

 this soon resolves itself into a mediocre sample of the general 

 population. It may be, however, that there is a fallacy in the 

 theory, namely in the assumption that the degree of resemblance 

 observed is wholly due to heredity. Much resemblance may be. 

 due to similarity in nurture, to non-transmissible somatic modi- 

 fications which are re-impressed generation after generation by 

 peculiarities of environment, nutrition, and function. Pearl 

 (1915) and others have pointed out that heredity is not the 

 sole cause which can lead statistically to a significant correlation 

 between parent and offspring. Conklin (1918, p. 221) writes : 

 " The value of statistics depends upon a proper classification of 

 the things measured and enumerated, and if things which are 

 not commensurable are grouped together the results may be 

 quite misleading and worthless. Unfortunately Galton and 

 Pearson, as well as some of their followers, have not carefully 

 distinguished between hereditary and environmental characters.". 

 Jennings (1910) says : " Galton's laws of regression and ances- 

 tral inheritance are the product mainly of a lack of distinction 

 between two absolutely diverse things, between non-inheritable 

 fluctuations on the one hand" (our " somatic modifications ") 

 "and permanent genotypic differentiations" (our "germinal 

 variations and mutations ") "on the other." 



(b) Galton and Pearson pointed out that the generalisations 

 in question do not hold in lineages where very careful selection 

 has taken place, for in such cases the mean of the ancestry was 

 obviously different from that of the general population. 



(c) The law of ancestral inheritance was a statistical conclu- 

 sion intended to show the proportionate average contribution 



