242 
THE DESCENT OF MAN. 
Part L 
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, £ Eaces of Man,’ 1850, 
p. 473. 
41 See De Quatrefages on this head , 6 Eevne des Cours Scientifiques,’ 
Oct. 17, 1868, p. 731. 
42 Livingstone’s ‘ Travels and Kesearches in S. Africa, ’ 1857, p. 338, 
329. D’Orbigny, as quoted by Godron, ‘ De l’Espece,’ vol. ii. p. 266. 
