SKIN COLOUR 177 



mated with a coloured person, or if it is even more com- 

 plex, clearly then, Nature will have denied those rash 

 Biometricians, who imagined it was all so simple. 



There is yet another feature which introduces a 

 further complexity, and is indeed, the key to the whole 

 problem. Let us try to make it as clear as possible. 

 There is good evidence to show that colour in animals and 

 plants is due to the interaction of two bodies, both 

 colourless. There is reason to believe that one of these may 

 be a ferment and the other a substance upon which the 

 ferment acts. It is possible that the ferment determines 

 the production of actual colour, and the other body — a 

 chromogen — determines whether the colour shall be black 

 or yellow, or some other hue. Colour cannot be produced 

 unless these two substances are simultaneously present 

 in the tissues of the individual, and the nature of the colour 

 and its intensity will depend upon the nature of these 

 bodies. An albino, for instance, may be carrying the 

 chromogens, but no ferment or ferments. Consequently, 

 in the absence of these latter, the skin will be colourless. 

 Now the European skin is not of the nature of the albino 

 skin, and it may possibly carry both chromogens and 

 ferments, and the light coloured skin of the European 

 may be due to the nature of these, or to the 

 presence of colour-reducing or colour- inhibiting factors. 

 In the negro we may also assume that both chromogens 

 and ferments are present, and the nature of these 

 is such that his skin is darkly coloured. Now if the 

 chromogens and ferments of the European and the negro 

 can be brought, by hereditary processes, into chemical 

 contact with each other, they will modify the negro and 

 European colour, and determine some other sort of colour, 

 that of the mulatto. 



Now the crucial point is this. If C stands for the 

 presence of a colour producer (ferment), and c stands for 

 its absence, and if D^ and D^ stand for the presence of 

 two colour determiners (chromogens), and d^ and d- stand 

 for their absence in the negro, then C and 0,0^ and d^ 

 and D- and d- are three allelomorphic pairs, so that 

 Di and d^, and C and c, and D- and d^, cannot occur 

 as pairs respectively in the same gamete. But we 

 have postulated that the European is also carrying 



