THE ELEMENTS OF COLOUR. I03 



produce upon Mankind some modifications of 

 colour, and of features. But we know also 

 that such changes are extremely slow. 

 Colour is in all the lower animals one of 

 the least constant — that is to say, one of 

 the most variable, — of external characters; 

 and under circumstances of domestication 

 changes of colour are sometimes sudden, 

 and are connected with causes altogether 

 unknown. But we have no evidence to 

 show that human colour is liable to changes 

 of a like kind. On the contrary, all ex- 

 perience seems to point to the conclusion 

 that varieties of complexion can only be 

 established very gradually, and we have no 

 absolute proof that a change from white 

 to negro blackness is possible at all. A 



