256 THE DESCENT OF MAN 



with corresponding differences of climate. Some little 

 weight may be given to such cases as that of the Dutch 

 I families, who, as we hear on excellent authority," have not 

 j undergone the least change of color after residing for three 

 i centuries in South Africa. An argument on the same side 

 may likewise be drawn from the uniform appearance in 

 various parts of the world of gypsies and Jews, though the 

 uniformity of the latter has been somewhat exaggerated." 

 A very damp or a very dry atmosphere has been supposed 

 to be more influential in modifying the color of the skin 

 than mere heat; but as D'Orbigny in South America, and 

 Livingstone in Africa, arrived at diametrically opposite 

 conclusions with respect to dampness and dryness, any con- 

 clusion on this head must be considered as very doubtful." 

 Various facts, which I have given elsewhere, prove that 

 the color of the skin and hair is sometimes correlated 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 from the deadly influence 

 of the miasma of their native countries, during a long series 

 of generations. 



I afterward found that this same idea had long ago 

 occurred to Dr. Wells." It has long been known that ne- 

 groes, and even mulattoes, are almost completely exempt 

 from the ygllow-feveiL, so destructive in tropical America." 

 They likewise escape to a large extent the fatal intermittent 



" Sir Andrew Smith, as quoted by Knox, "Eacea of Man," 1850, p. ilZ. 



^ See De Quatrefages on this head, "Revue des Cours Scientifiques, " Oct. 

 11, 1868, p. 131. 



** Livingstone's "Travels and Researches in S. Africa," ISSI, pp. 338, 329. 

 D'Orbigny, as quoted by Godron, "De I'Esp^ce," vol. ii. p. 266. 



'* See a paper read before the Royal Soo. in 1813, and published in his 

 Essays in 1818. I have given an account of Dr. Wells's views in the Historical 

 Sketch (p. xvi.) to my "Origin of Species." Various cases of color correlated 

 with constitutional peculiarities are given in my "Variation of Animals 

 wnder Domestication," vol. ii. pp. 227, 335. 



" See, for instance, Nott and Gliddon, "Types of Mankind," p. 68. 



