156 



THE PRINCIPLES OF HEREDITY 



259. The following table shows the amount of child 

 sickness and mortality among the whites in India : 



STRENGTH, SICKNESS, AND MORTALITY OF CHILDREN 

 IN THE ARMY OF INDIA. 



260. It is not necessary to pursue this subject any farther. 

 The facts are indisputable. No one doubts that races which 

 dwell within the area infested by any prevalent and death- 

 dealing disease are more resistant to it than races from 

 beyond the area. The only possible question is as to how 

 this difference in resisting-power arose. It is commonly 

 said to be due to "acclimatization," a word which, when 

 applied to races, even by the ignorant, is practically a 

 synonym for evolution. A race that has undergone accli- 

 matization is of course one that has undergone evolution. 

 But this acclimatization, this evolution, is popularly supposed 

 to result from the accumulation of acquired traits. It is now 

 sufficiently clear that this is not the case. On the contrary, 

 it is due solely to Natural Selection. We have already 

 maintained that Natural Selection can act only when varia- 

 tions are spontaneous that is when they are not caused by 

 the influence of the environment. The study of disease, as 

 we shall now proceed to show, demonstrates this point very 

 clearly. 



