220 THE DESCENT OF MAN. 



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 conclusion on this head must 

 be considered as very doubtful, f 



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. J It has long been known that 

 negroes, and even mulattoes are almost completely exempt 

 from the yellow fever, so destructive in tropical America. 

 They likewise escape to a large extent the fatal intermit- 

 tent fevers that prevail along at least 2,600 miles of the 

 shores of Africa, and which annually cause one-fifth of the 

 white settlers to die and another fifth to return home 

 invalided. || This immunity in the negro seems to be partly 

 inherent, depending on some unknown peculiarity of con- 

 stitution and partly the result of acclimatization. Pouchetl" 

 states that the negro regiments recruited near the Soudan 



* See De Quatref ages on this head, ' ' Revue des Cours Scien- 

 tifiques," Oct. 17, 1868, p. 731. 



f Livingstone's "Travels and Researches in S. Africa," 1857, pp. 

 338, 339. D'Orbigny, as quoted by Godron, "De 1'Espece," vol. ii, 

 p. 266. 



% See a paper read before the Royal Soc. in 1813 and published in 

 his Essays in 1818. I have given an account of Dr. Wells' views in 

 the Historical Sketch (p. 16) to uiy " Origin of Species." Various 

 cases of color correlated with constitutional peculiarities are given in 

 my " Variation of Animals under Domestication," vol. ii, pp. 227,335. 



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



I Maj. Tulloch, in a paper read before the Statistical Society , April 

 20, 1840, and given in the " Athenaeum," 1840, p. 353. 



TT" The Plurality of the Human Race " (translate), 1864, p 60. 



