BEGINNINGS OF INTELLIGENCE 165 



a consideration of the role of pleasure and pain as agents of 

 accommodation. 



The tendency of animals to repeat acts which result in 

 pleasure and to discontinue or inhibit acts which bring them 

 pain is a fundamental feature of behavior on the utility of 

 which it would be superfluous to comment. But why do 

 animals behave in this fortunate manner, and how did they 

 come to acquire the faculty of so behaving? To our ordinary 

 plain way of thinking it appears sufficient to say that a dog 

 eats meat because he likes it, and that he runs away from the 

 whip to avoid its painful incidence upon his integument. 

 These acts are such natural and obvious things to do under 

 the circumstances that to inquire why the animal does what 

 it likes and avoids what is disagreeable may seem a sort 

 of philosophic quibble which only a mind "debauched by 

 learning" would think of indulging in. But a little con- 

 sideration will show that we have here a real and very 

 knotty problem, or rather set of problems, of the greatest 

 importance to the student of genetic psychology. 



There are few better illustrations of the modification of 

 behavior through experiences of pleasure and pain than that 

 afforded by the behavior of young chicks, which has been 

 so well studied by Lloyd Morgan. A young chick when 

 first hatched has the instinct to peck at all sorts of objects 

 of about a certain size. If an object is a little too large the 

 chick may hesitate. Should it venture to peck at the object 

 and derive a pleasant taste from it the hesitation in the pres- 

 ence of similar objects becomes reduced and will finally 

 disappear. If the chick in the course of its pecking seizes 

 a caterpillar having a nauseous taste it is much less apt to 

 seize a similar caterpillar a second time. The painful or 

 unpleasant experience it derives in some way inhibits further 

 action toward that class of objects. 



