PROBLEM I. The Simplest Forms of 



Instinctive behavior. The spider spins 

 its web in a most elaborate design; if 

 you have ever read a description of how 

 it is done vou will know how compli- 

 cated the process is. You are obliged to 

 struggle over even an explanation of how 

 it is done. How could the spider learn 

 to do it? If a young spider which has 

 never seen a web is placed by itself, it 

 will in time spin a web like the one spun 

 by its parents. If it is raised with spiders 

 of another species which use a different 

 design it does not imitate what goes on 

 around it; it spins the kind its parents 

 spun. This is pretty good evidence that 

 the spider did not learn how to spin its 

 web. 



Web spinning is obviously unlearned, 

 but it is more than a simple reflex. It 

 seems to be the product of a reflex act 

 followed by a second reflex of a slightly 

 different kind and a third and so on until 

 the web is completed. When the first 

 thread has been spun, it serves as a new 

 stimulus and the second step is per- 

 formed. This provides a different stimu- 

 lus and the third reflex is set off. The 

 spider's reflexes go on in regular order. 

 We can use the term instinctive behavior 

 for such a chain or series of reflexes. 

 Each act of the instinctive behavior is an 

 inborn and unlearned response. The ani- 

 mal acts according to a pattern with 

 which it seems to have been born. 



Instinctive behavior requires no intelli- 

 gence. It is clear that instinctive behavior 

 is unlearned. Furthermore, experiments 

 furnish evidence that animals do not 

 show thought or intelligence in instinc- 

 tive behavior. Wells, Huxley, and Wells 

 in their book The Science of Life tell 

 of an interesting experiment which shows 



Behavior in Animals 



M 



Fig. 248 A wasp's nest is built by a succession 

 of reflex acts. How can we know that the wasp's 

 behavior is instinctive, not learned? (American 



MUSEUM OF NATURAL HISTORY) 



that intelligence does not enter into in- 

 stinctive behavior. The bush turkey 

 hatches from an egg laid at the bottom 

 of a heap of decaying plant material. 

 After breaking through the shell, the 

 young bird wriggles up and out at the 

 top of the heap. Then it shakes itself 

 and runs off, seemingly to find protec- 

 tion. It is doing the correct thing. But is 

 it doing the correct thing because it is 

 using thought and intelligence? The an- 

 swer is given by the following observa- 

 tions. The young bird was caught and 

 again placed at the bottom of the pile 

 from which it had just wriggled. It 

 stayed there without a struggle. It was 

 born with a pattern of behavior for 

 wriggling upward as it left the shell, and 

 it did that. But there is no pattern for 

 doing this a second time. If the baby 

 bush turkey in the experiment had not 

 been rescued, it might have remained 

 under the pile of decaying material. It 

 was not using intelligence when it pushed 

 its way out the first time, it was just 

 performing an inborn, unlearned act. 

 Because of this and other similar obser- 



