EVOLUTION AGAINST DISEASE 135 



216. Or is the doctrine of the causation of variations by 

 the direct action of the environment on the germ-plasm the 

 true doctrine ? Do all diseases, lethal or non-lethal, produce 

 racial degeneration ? 



217. The evidence is decisive. The doctrine of spontane- 

 ous variations, and therefore of evolution by the agency of 

 Natural Selection, is beyond doubt the true doctrine. There 

 is not an iota of evidence that any race whatsoever has 

 undergone degeneration through the action of any disease, 

 nor that the acquirement of immunity during any number of 

 generations has resulted in an evolution of inborn immunity. 

 On the contrary, every race, that has been exposed to a lethal 

 disease, is resistant to that particular disease precisely in 

 proportion to its past experience of it. When the disease is 

 one against which immunity cannot be acquired, the race has 

 undergone an evolution of inborn immunity ; thus Europeans 

 who have suffered severely from tuberculosis for thousands 

 of years, resist infection by it, or when infected recover from 

 it more easily than African Negroes who have suffered less, 

 and much more easily than American Indians, who until 

 lately had no experience of the disease. When the disease 

 is one against which immunity can be acquired, the race has 

 undergone an evolution of the power of acquiring immunity, 

 never of inborn immunity ; thus English children, whose race 

 has long been afflicted by measles and whooping-cough, con- 

 tract those maladies as easily as Polynesians to whom they 

 were familiarized only during the last century. But, whereas 

 English children, as a rule, recover readily, 'Polynesians perish 

 in great numbers. When the disease is non-lethal no effect 

 on the race can be observed. Thus Polynesians are infected 

 as easily and recover as easily, but not more nor less easily, 

 than Englishmen from chicken-pox. 



218. It is easy to give chapter and verse. We have only 

 to glance at the evidence relating to a few of the more 

 important diseases. Malaria. Man's evolution against 

 malaria is more striking and conspicuous than that oc- 

 casioned by any other disease, and that for two reasons. 

 First, because, in many districts infested by its microbes, it 

 is so prevalent and virulent that no man resident in them 

 escapes infection unless he is immune nor death unless he is 

 resistant. The elimination of the unfit therefore has 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, pro- 

 tected by their deadly climate from the fate that has befallen 



