NATURAL HISTOEY OF MAN. 439 



in races of men. Take, for example, the colour of the skin, 

 to which the latter class of arguments chiefly applies, and 

 the diversities of which are at least as prominent as those of 

 figure. The extreme contrasts in this case are the Negro 

 and the Albino. The latter is clearly an accidental variety ; 

 but, as such, becomes from its marked characters a valuable 

 exponent of all other varieties of colour. That part of the 

 structure of the skin, which is called the pigment-cell, is 

 evidently capable of undergoing great changes in its secre- 

 tions from climate, manner of life, and those more mysterious 

 causes connected with generation and the hereditary trans- 

 mission of bodily features and peculiarities, the influence of 

 which we everywhere see, but which we cannot yet subject 

 to specific laws. Time is manifestly an element of great 

 importance here. The amount of change of which we have 

 evidence, even within short periods, is the proof of the capa- 

 city for far greater change where time is prolonged, and a 

 community of men so placed as to be exposed continually to 

 the operation of the same physical causes. 



When to these considerations we add the facts upon which 

 we have already so much dwelt, viz. that nature produces 

 frequent varieties in all races as striking as are the extreme 

 diversities amongst them ; and 2ndly, that there is an entire 

 continuity in the gradations which occur in nature from one 

 diversity to another, we present the argument in the most 

 complete form it can assume. Thus, to take a single but 

 striking example of the first case. A Negro may have an 

 Albino offspring without pigment-cells; a fact including 

 at once all those minor varieties of colour which are so fami- 

 liar to us in the same community, and even in the same 

 family. The continuous gradations of colour from the Negro 

 to the native of northern Europe, though less obvious to 

 common knowledge, have been so well substantiated by tra- 

 vellers and men of science, that no remaining doubt can 



