THE EVOLUTION OF INTELLIGENCE 121 



tion of institutions, to preserve tradition and modify its 

 coercive influence by rational discussion, and incidentally it has 

 afforded him the most powerful single tool for creative indi- 

 vidual thinking. 



The striking character of the difference between typical 

 human processes of inference and those by which animals ac- 

 quire wholly new reactions may be illustrated by a single 

 example. Here is a dog shut up in a cage with his food just 

 outside the door. To open the door and satisfy his hunger 

 involves pulling a cord which lifts a latch. No matter how 

 obvious the arrangement to human vision, the dog may thrash 

 about for a long time in the neighborhood of the cord, biting 

 and clawing the various parts of the cage, until by accident he 

 may seize the cord in his teeth and forthwith escape. A human 

 being having once found a single act which would thus open 

 the door would ordinarily require no second experience in- 

 stantly to repeat the success. But the animal may need many 

 such trials before establishing the correct response, showing 

 that there is very slow discernment, or possibly none, of the 

 real relation of the cord to the opening of the door. 



Now human beings do many things quite similar to the ran- 

 dom activities of the animal in the cage. Many a child at- 

 tempting to solve a mathematical problem does exactly the 

 same thing and comes upon the correct result, if at all, quite 

 accidentally and as the outcome of a kind of mental fumbling. 

 Indeed, all elaborate thought processes inevitably have in them 

 much of this more or less haphazard experimental venturing. 

 But the point is that once the human being clearly sees the rela- 

 tion involved, he can immediately repeat successfully the pro- 

 cess and generally carry over the principle to other similar but 

 not identical problems. It is doubtful if animals ever do just 

 this thing. Even their powers of imitation are far less than is 

 commonly supposed. 



So, despite the structural similarity of the brain of man and 



