64 HEREDITY AND ENVIRONMENT 



reptiles, birds and mammals, has been studied 

 and in all cases it is found that their method 

 of responding to stimuli is not at first really 

 purposive and intelligent but by the gradual 

 elimination of useless responses and the 

 preservation (or remembering) of useful ones 

 the behavior may come to be purposive and 

 intelligent. 



Thorndike found that when dogs, cats and 

 monkeys were confined in cages which could 

 be opened from the inside by turning a button, 

 or pressing upon a lever, or pulling a cord, 

 they at first clawed around all sides of the cage 

 until by chance they happened to operate the 

 mechanism which opened the door. There- 

 after they gradually learned by experience, 

 that is, by trial and error, and finally by trial 

 and success, just where and how to claw in 

 order to get out at once. When a dog has 

 learned to turn a button at once and open a 

 door we say he is intelligent, and if he can 

 learn to apply his knowledge of any particular 

 cage to other and different cages, a thing 

 which Thorndike denies, we should be justified 

 in saying that he reasons, though in this case 



