46o THE GRAMMAR OF SCIENCE 



{d) That, almost as a corollary from {c), inheritance in 

 a line through one sex is prepotent over inheritance in the 

 same degree with a change of sex. That a man in eye- 

 colour more closely resembles his paternal than his 

 maternal grandfather ; a woman more closely resembles 

 her maternal grandmother than her paternal grandmother. 

 Again, a nephew is more like his paternal uncle than his 

 paternal aunt ; a niece like her maternal aunt than her 

 maternal uncle. 



Such principles as these will show how definite and 

 important are the results which can be drawn from a 

 quantitative study of heredity.^ But we must be very 

 cautious when we are dealing with such cases how we 

 proceed from observed numerical prepotency to reason on 

 its causes. Thus the reader may have noticed that I 

 have omitted in the above table the inheritance of cephalic 

 index from father to son and to daughter. The mean 

 value of these coefficients as deduced from North American 

 Indians is .137. We might argue from this that the 

 mother is prepotent. But Dr. Boas in sending me the 

 data for these Indians wrote : — 



I am afraid that your results may bring out the looseness of family 

 relations. I should not be surprised if the relation between father 

 and child were much lower than that between mother and child, 

 because often another person is actually the father of the child. 



Thus the reduction in the intensity of heredity from 

 somewhere about .3 to .137 does not here signify the 

 prepotency of the mother. We have reached, instead, a 

 measure of conjugal fidelity in the race, and we can (after 

 exercising a little algebraic ingenuity) assert that in about 

 54 per cent of cases the Indian woman is not faithful to 

 her putative husband ! 



Again, the average intensity of heredity in coat-colour 

 for the sire and offspring in the case of Basset bloodhounds 



1 The social consequences are also very significant ; insanity in a woman's 

 maternal aunt should, for example, be a more serious barrier to matrimony 

 than insanity in her maternal uncle, though both may be serious enough. 

 Gout in a man's father's father is of more consequence to him than when it 

 occurs in his mother's father. 



