2o6 MENDELISM chap. 



behaves as though it were due to a Mendelian 

 factor. 



Even this fact is of considerable importance, for 

 it at once suggests that the present systems of classi- 

 fication of eye-colours, to which some anthropologists 

 attach considerable weight, are founded on a purely 

 empirical and unsatisfactory basis. Intensity of 

 colour is the criterion at present in vogue, and it is 

 customary to arrange the eye-colours in a scale of 

 increasing depth of shade, starting with pale greys 

 and ending with the deepest browns. On this 

 system the lighter greens are placed among the 

 blues. But we now know that blues may differ from 

 the deep browns in the absence of only a single 

 factor, while, on the other hand, the difference 

 betwefen a blue and a green may be a difference 

 dependent upon more than one factor. To what 

 extent eye-colour may be valuable as a criterion of 

 race it is at present impossible to say, but if it is 

 ever to become so, it will only be after a searching 

 Mendelian analysis has disclosed the factors upon 

 which the numerous varieties depend. 



A discussion of eye-colour suggests reflections of 

 another kind. It is difficult to believe that the 

 markedly different states of pigmentation which 

 occur in the same species are not associated with 

 deep-seated, chemical differences influencing the 

 character and bent of the individual. May not these 

 differences in pigmentation be coupled with and so 

 become in some measure a guide to mental and 

 temperamental characteristics ? In the National 

 Portrait Gallery in London the pictures of cele- 

 brated men and women are largely grouped accord- 



