174 NATURAL SELECTION VIII 
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 
