Many of the so-called instincts in animals are either simple reflexes or 

 combinations of reflexes. It is characteristic of many of the adaptive and 

 useful activities that they are not learned. Young chicks, for example, peck- 

 ing at food or walking about, perform the acts about as well the first time 

 as later. Moreover, all the members of the species normally act in the same 

 way. Apparently instincts depend upon special sets of structures that are 

 characteristic of the species. Yet we know that animals do change their 

 instincts. 



How Do Organisms Change through Experience? 



Changing Instincts A pike was placed in an aquarium with a num- 

 ber of smaller fish. The pike swallowed his neighbors. A glass partition 

 was then put in, separating the pike from the smaller animals. The pike 

 would dart at them, however, and was often stunned by striking the glass 

 plate. But in time he stopped darting after the small fish. Later the parti- 

 tion was removed. Yet the pike always turned aside when he approached 

 one of the little fellows. Nothing now prevented his eating them except his 

 past experience. That is to say, his natural behavior had become modified. 



The bruised pike shuns small fry; a burnt child dreads the fire. Acts 

 which have unpleasant accompaniments come to be avoided. Certain natural 

 impulses become repressed. On the other hand, acts associated with feelings 

 of satisfaction come to be performed more readily. This is the principle that 

 you would use if you tried to teach a dog or a colt a new trick. If you re- 

 ward the animal with praise or a piece of sugar every time it does what you 

 want it to do, it will be more likely to repeat the performance. At last the 

 acquired trick takes the place of the animal's earlier spontaneous behavior. 



A baby crying for food will at first keep on crying until something ac- 

 tually touches his mouth. In a few days he stops crying as soon as he hears 

 his mother's voice. Some will say that the child "recognizes" his mother's 

 voice, or that he "knows" that she is about to feed him. But from observa- 

 tions and experiments with the young of many animals, including babies, 

 we say rather that the sound has become associated with the feeding. And 

 this association of two experiences has modified the natural response. A new 

 stimulus — in this case, a particular sound — now acts as a substitute for the 

 original stimulus to stop the crying or to start the sucking. This new mode 

 of responding, the new trick of behavior, is sometimes called a habit. This 

 familiar word habit is commonly used in a broad (and not always a very 

 exact) sense. But from experiments with many animals, including human 

 beings, we have learned a great deal about how conduct is modified. 



Conditioning The most famous and extensive of these experiments, 

 mostly with dogs, were directed by the Russian physiologist Ivan Petrovich 

 Pavlov (1849-1936). They started from the well-known fact that a dog's 



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