4 8 



Heredity and Environment 



gradual elimination of useless responses and the preservation (or 

 remembering) of useful ones the behavior may come to be pur- 

 posive and intelligent. 



Intelligence Develops from Trial and Error. Thorndike found 

 that when dogs, cats or 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. Thereafter 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 intelligence and reason are 

 founded upon memory of many past experiences, of many trials 

 and errors and of a few trials and successes. 



FIG. 21. DIAGRAM OF THE AVOIDING REACTION OF Paramecium. A is a 

 solid object or other source of stimulation. 1-6, successive positions oc- 

 cupied by the animal. The rotation on the long axis is not shown. (After 

 Jennings.) 



