242 THE DESCENT OF MAN. Paet I. 



rejected chiefly because the distribution of the variously 

 coloured races, most of whom must have long inhabited 

 their present homes, does not coincide with correspond- 

 ing differences of climate. Weight must also be given 

 to such cases as that of the Dutch families, who, as 

 we hear on excellent authority, 40 have not undergone 

 the least change of colour, after residing for three cen- 

 turies in South Africa. The uniform appearance in 

 various parts of the world of gypsies and Jews, though 

 the uniformity of the latter has been somewhat exagge- 

 rated, 41 is likewise an argument on the same side. A 

 very damp or a very dry atmosphere has been supposed 

 to be more influential in modifying the colour of the 

 skin than mere heat ; but as D'Orbigny in South 

 America, and Livingstone in Africa, arrived at diame- 

 trically opposite conclusions with respect to dampness 

 and dryness, any conclusion on this head must be con- 

 sidered as very doubtful. 42 



Various facts, which I have elsewhere given, prove 

 that the colour of the skin and hair is sometimes corre- 

 lated in a surprising manner with a complete immunity 

 from the action of certain vegetable poisons and from 

 the attacks of certain parasites. Hence it occurred to 

 me, that negroes and other dark races might have 

 acquired their dark tints by the darker individuals 

 escaping during a long series of generations from 

 the deadly influence of the miasmas of their native 

 countries. 



I afterwards found that the same idea had long ago 



40 Sir Andrew Smith, as quoted by Knox, ' Races of Man,' 1850, 

 p. 473. 



41 See De Quatrefages on this head, • Revue des Cours Scientifiques,' 

 Oct. 17, 1868, p. 731. 



4 " Livingstone's ' Travels and Researches in S. Africa,' 1857, p. 338, 

 329. D'Orbigny, as quoted by Godron, • De l'Espece,' vol. ii. p. 266. 



