234 THE DESCENT OF MAN. [Part 1. 



are almost completely exempt from the yellow fever, which 

 is so destructive in tropical America, has long been known. 44 

 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 fiftn to return home in- 

 valided. 45 This immunity in the negro seems to be partly 

 inherent, depending on some unknown peculiarity of con- 

 stitution, and partly the result of acclimatization. Pou- 

 chet 46 states that the negro regiments, borrowed from the 

 Viceroy of Egypt for the Mexican War, which had been 

 recruited near the Soudan, escaped the yellow fever al- 

 most equally well with the negroes originally brought 

 from various parts of Africa, and accustomed to the cli- 

 mate of the West Indies. That acclimatization plays a 

 part is shown by the many cases in which negroes, af- 

 ter having resided for some time in a colder climate, 

 have become to a certain extent liable to tropical fevers. 47 

 The nature of the climate under which the white races 

 have long resided, likewise has some influence on them ; 

 for, during the fearful epidemic of yellow fever in Deme- 

 rara during 1837, Dr. Blair found that the death-rate of 

 the immigrants was proportional to the latitude of the 

 country whence they had come. With the negro the im- 

 munity, as far as it is the result of acclimatization, implies 



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 'Va- 

 riation of Animals under Domestication,' vol. ii. pp. 227, 335. 



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



45 Major Tulloch, in a paper read before the Statistical Society, April 

 5s0, 1840, and given in the 'Athenaeum,' 1840, p. 353. 



46 ' The Plurality of the Human Race ' (translat.), 1864, p. 60. 



47 Quatrefages, 'Unite de l'Espece Humaine,' 1861, p. 205. "Waltz, 

 ' Introduct to Anthropology,' translat. vol. i. 1863, p 124. Livingstone 

 gives analogous cases in his ' Travels.' 



