242 
THE DESCENT OF MAN. 
Part 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, ilS 
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 exag'g e ' 
rated , 41 is likewise an argument on the same side. 
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 Afiica, arrived at diame- 
trically opposite conclusions with respect to dampness 
and dryness, any conclusion on this head must be com 
sidered as very doubtful . 44 
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 iron 1 
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 individual 5 
escaping during a long series of generations iron 1 
the deadly influence of the miasmas of their native 
countries. 
I aiterwards found that the same idea had long a S° 
4(1 Sir Andrew Smith, as quoted by Knox, ‘ Paces of Man,’ 
p.473. 
41 See De Quatrefages on this bead, ‘ Revue des Cours Scicnti£<l lieB ’ 
Oct. 17, 18G8, p. 731. 
4 - Livingstone’s 1 Travels and Researches in S. Africa,’ 1857, p- ^ ’ 
329. D’Orbigny, as quoted by Godron, * De l’Espcce,’ vol. ii. P- 
