174 NATURAL SELECTION vin 



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therefore, have become the subjects of natural selection. 

 For it is evident that such qualities would be for the well- 

 being of man, would guard him against external enemies, 

 against internal dissensions, and against the effects of incle- 

 ment seasons and impending famine, more surely than could 

 any merely physical modification. Tribes in which such 

 mental and moral qualities were predominant would there- 

 fore have an advantage in the struggle for existence over 

 other tribes in which they were less developed would live 

 and maintain their numbers, while the others would decrease 

 and finally succumb. 



Again, when any slow changes of physical geography or 

 of climate make it necessary for an animal to alter its food, 

 its clothing, or its weapons, it can only do so by the occur- 

 rence of a corresponding change in its own bodily structure 

 and internal organisation. If a larger or more powerful 

 beast is to be captured and devoured, as when' a carnivorous 

 animal which has hitherto preyed on antelopes is obliged from 

 their decreasing numbers to attack buffaloes, it is only the 

 strongest who can hold, those with most powerful claws 

 and formidable canine teeth that can struggle with and over- 

 come such an animal. Natural selection immediately comes 

 into play, and by its action these organs gradually become 

 adapted to their new requirements. But man, under similar 

 circumstances, does not require longer nails or teeth, greater 

 bodily strength or swiftness. He makes sharper spears, or a 

 better bow, or he constructs a cunning pitfall, or combines in 

 a hunting party to circumvent his new prey. The capacities 

 which enable him to do this are what he requires to be 

 strengthened, and these will, therefore, be gradually modified 

 by natural selection, while the form and structure of his 

 body will remain unchanged. So, when a glacial epoch comes 

 on, some animals must acquire warmer fur, or a covering of 

 fat, or else die of cold. Those best clothed by nature are, 

 therefore, preserved by natural selection. Man, under the 

 same circumstances, will make himself warmer clothing, and 

 build better houses, and the necessity of doing this will react 

 upon his mental organisation and social condition will ad- 

 vance them while his natural body remains naked as before. 



When the accustomed food of some animal becomes scarce 



