380 THE MA.INTENANCE OF THE INDIVIDUAL 



But this behavior was only hroufilit about through tlie presentation 

 of food many times in succession at the same time or just after the 

 ringing of the bell, or the use of the colored plate, thus forming 

 an association between food and bell, or food and plate. Eventually 

 when food was not presented but the bell rang, or the plate was 

 shown, saliva would flow from the parotid gland just as if food was 

 present. The reflex established originally with food was changed 

 through association of food with bell or plate. Thus Pavlov estab- 

 lished a law of the conditioned reflex, which may be stated thus : 

 "If a new indifferent external stimulus is many times present along 

 with one which has also a definite response, the subsequent presenta- 

 tion of the new stimulus causes the reflex to be given." 



Conditioned reflexes have been demonstrated in forms as simple 

 as the Ameba, earthworm, crab, snail, octopus, as well as in higher 

 animals. It is, however, unlikely that conditioning plays a very 

 important part in the lives of lower animals. In the case of fishes, 

 reptiles, amphibians, and vertebrates, the "training" which comes 

 through the conditioning of behavior may play a minor part. In the 

 highest vertebrates, apes and men, conditioning undoubtedly plays a 

 very definite part in the learning process. Experiments made in 

 Pavlov's laboratory have shown that while a dog may take from 

 thirty to one hundred trials before it is conditioned to food, a young 

 child may show the same conditioned effect in from ten to twenty-five 

 trials. 



Are Behaviors Adaptive Responses? 



It is easy to show that all responses to stimuli are useful to a plant 

 and, therefore, enable it to adapt itself more easily to the environment 

 in which it lives. The turning of stems and leaves toward light, the 

 "seeking" of roots for water, the twining movements of plants are 

 all well-known examples. 



When it comes to animals, there are two views of their response to 

 stimuli, one mechanistic, the other adaptive. The first considers the 

 organism to be a machine that responds blindly to the various physical 

 and chemical stimuli which impinge upon it, regardless of the conse- 

 quence to the organism. This is much easier to see in simple animals 

 than in more complex ones, because in the latter the behavior of the 

 organism is influenced not only by different combinations of stimuli 

 but also by the reinforcement or weakening of stimuli. The behavior 

 of the organism at a given time will be determined, not by a single 



