314 THE ACTION OF NATURAL 



selection immediately comes into play, and by its 

 action these organs gradually become adapted to their 

 new requirements. But man, under similar circum- 

 stances, 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 se- 

 lection," 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 cover- 

 ing 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 him- 

 self warmer clothing, and build better houses ; and 

 the necessity of doing this will react upon his mental 

 organization and social condition will advance them 

 while his natural body remains naked as before. 



When the accustomed food of some animal becomes 

 scarce or totally fails, it can only exist by becoming 

 adapted to a new kind of food, a food perhaps less 

 nourishing and less digestible. " Natural selection " 

 will now act upon the stomach and intestines, and all 

 their individual variations will be taken advantage of, 

 to modify the race into harmony with its new food. 

 In many cases, however, it is probable that this can- 

 not be done. The internal organs may not vary quick 

 enough, and then the animal will decrease in numbers, 



