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 prevalent 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, however 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 different races of mankind differ vastly in their powers of resisting the disease, and that those races that have had extended
