CHAPTER V 



Malaria. — Man's evolution against malaria is more 

 striking and conspicuous than that occasioned by any 

 other disease, and this for two reasons. Firstly, because 

 in many districts infested by its microbes, it is so pre- 

 valent and virulent that no one resident in them escapes 

 infection unless he is immune, or death unless he is 

 resistant ; the elimination of the unfit has therefore 

 been very thorough, and presumably it has been very 

 prolonged, since in such districts the inhabitants, how- 

 ever much they may have warred among themselves, 

 have dwelt secure, protected by their deadly climate 

 from the fate that has befallen so many aboriginal tribes 

 — e. g, the aborigines of Great Britain, — extermination 

 by immigrant hordes. Evolution against malaria has 

 therefore been very considerable. Secondly, the illness 

 occasioned by the disease is of a very sudden and 

 marked character, and therefore observers are easily 

 able to contrast its effects on individuals of different 

 races, and to perceive how much more resistant are 

 those races which have had prolonged experience of it 

 than those to which it is strange. 



So considerable has the evolution against malaria 

 been in various parts of the world that it is scarcely 

 necessary to bring forward evidence in proof of it. 

 Nothing indeed can be plainer than that diflferent races 

 of mankind differ vastly in their powers of resisting the 

 disease, and that those races that have had extended 



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