CHAPTER VII. 



Natural Selection (continued) — Its Influence on the Corporeal Side of Man — 

 Disease, a Necessary Evil — Active Operation of Natural Selection in con- 

 sequence of Instability of the Environment — Perfect Adaptation impos- 

 sible — Illustrations. 



We have now to consider how far natural selection operates 

 on the corporeal side of man, and this question is, from the 

 medical point of view, of even greater importance than how far 

 it influences the mental side, since the great majority of the 

 diseases with which we have to do are diseases of the body. 



That natural selection has always been actively at work on 

 primitive man is evidenced by the stationary state of the 

 population. For, since the human race tends to increase in 

 geometric ratio, the population can only be kept at a fixed 

 level by a terrific destruction of life, and such destruction must 

 necessarily, on the whole, be a destruction of the least fit. 

 Warfare has doubtless been the chief check to increase. If we 

 look into the past history of man we see one continued conquest 

 of the weaker. Tribe has conquered tribe, nation, nation ; and 

 often enough such conquest has led to the actual extermina- 

 tion of the conquered. This may arise in a threefold 

 way — (i) by actual violent destruction, (2) through long- 

 continued subsequent oppression, or (3) through the inability 

 of the conquered to adapt themselves to the mode of life of 

 the conquerors ; thus, the coloured races often die out in con- 

 tact with the white man, not so much from destruction in 

 actual warfare as from an inability to adapt themselves to his 

 ways. 



Among savage races the continued warfare has doubtless, on 

 the whole, led to a survival of the corporeally fittest, although 

 sagacity has certainly played a not inconsiderable part in the 

 result. Among the civilized, however, victory rather belongs to 



