EVOLUTION AGAINST DISEASE 139 



ous districts of India, where the Mahomedan and Hindoo 

 population suffer in the same degree as foreigners. This is 

 not the less true for the Malay and Mongol stocks, and for 

 the native (Indian) population of North and South America. 

 The predisposition is least for the Ethiopian race, which, 

 though it by no means enjoys an absolute immunity from the 

 disease, is still effected by it, ceteris parihis, less frequently, 

 less readily, and less severely than other races ; and to this 

 many experiences have unquestionably testified, not only in 

 Senegambia, the West Coast of Africa, Nubia, and other 

 parts of its native habitat, but also in the malarious regions 

 of the tropics, whither they have emigrated. This relative 

 immunity from malarial fever on the part of the Negro race, 

 is an acquired, not a congenital one, as we may learn from the 

 frequent cases of sickness and death from this disease among 

 the children of the Negroes in Senegambia. But the same 

 immunity is enjoyed by the natives of all malarial regions, 

 so far as concerns their native home, and such other localities 

 as are affected by malaria less severely than it ; so that one 

 might almost formulate a general rule that the predisposition 

 to malarial sickness becomes weaker in proportion as the 

 individual has been continuously exposed, from birth to 

 maturity, to more or less severe malarial influences, without 

 suffering from them to any considerable extent." * 



224. The passage last quoted furnishes an example of facts 

 which may be accepted, but inferences which must be dis- 

 puted. The sweeping generalization that the " relative 

 immunity from malarial fever on the part of Negroes is an 

 acquired not a congenital one " is certainly not correct. 

 Characters which appear late in the development of the 

 individual are not necessarily acquired. The superior im- 

 munity, or much of it, exhibited by adult Negroes may be, 

 and probably is, as truly congenital as are their permanent 

 teeth or their beards. That some increase of resisting power 

 may be acquired against malaria by continual residence in its 

 presence is rendered certain by the fact that natives of 

 countries infested by it exhibit greater susceptibility when 

 returning from a residence abroad than do their compatriots, 

 or than they themselves exhibited before they left their 

 homes; but even this acquired character, like all use-acquire- 

 ments, depends on an inborn trait developed by Natural 

 Selection, for Negroes whose race has long been exposed to 

 malaria exhibit greater powers of acquiring it than Europeans. 2 



225. Tubercidosis. Man's evolution against tuberculosis is 



1 Hirsch, vol. i., 243-4. 2 See 290 (footnote). 



