Chap. V. 
INTELLECTUAL FACULTIES. 
159 
The lower animals, on the other hand, must have 
their bodily structure modified in order to survive under 
greatly changed conditions. They must be rendered 
stronger, or acquire more effective teeth or claws, in 
order to defend themselves from new enemies ; or they 
must be reduced in size so as to escape detection and 
danger. When they migrate into a colder climate they 
must become clothed with thicker fur, or have their 
constitutions altered. If they fail to be thus modified, 
they will cease to exist. 
The case, however, is widely different, as Mr. Wal- 
lace has with justice insisted, in relation to the intel- 
lectual and moral faculties of man. These faculties are 
variable ; and we have every reason to believe that the 
variations tend to be inherited. Therefore, if they were 
formerly of high importance to primeval man and to 
his ape-like progenitors, they would have been per- 
fected or advanced through natural selection. Of the 
high importance of the intellectual faculties there can 
be no doubt, for man mainly owes to them his pre- 
eminent position in the world. We can see that, in 
the rudest state of society, the individuals who were the 
most sagacious, who invented and used the best weapons 
or traps, and who were best able to defend themselves, 
w r ould rear the greatest number of offspring. The tribes 
which included the largest number of men thus endowed 
would increase in number and supplant other tribes. 
Numbers depend primarily on the means of subsistence, 
and this, partly on the physical nature of the country, 
but in a much higher degree on the arts which are there 
practised. As a tribe increases and is victorious, it is 
often still further increased by the absorption of other 
tribes . 2 The stature and strength of the men of a tribe 
2 After a time the members or tribes which are absorbed into another 
tribe assume, as Mr. Maine remarks (‘ Ancient Law,’ 1861, p. 131), that 
they are the co-descendants of the same ancestors. 
