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, 
