1/5 THE PROBLEM 



the opposite way. The salivary response to the sound of a bell 

 cannot, therefore, be due to a mechanism of fixed properties. 



A rat selected at random for an experiment in maze-running 

 can be taught to run either to right or left by the use of an appro- 

 priately shaped maze. Further, once trained to turn to one side 

 it can be trained later to turn to the other. 



Perhaps the most striking evidence that animals, after training, 

 can produce behaviour which cannot possibly have been inborn 

 is provided by the circus. A seal balances a ball on its nose for 

 minutes at a time; one bear rides a bicycle, and another walks 

 on roller skates. It would be ridiculous to suppose that these 

 reactions are due to mechanisms both inborn and specially per- 

 fected for these tricks. 



Man himself provides, of course, the most abundant variety of 

 learned reactions: but only one example will be given here. If 

 one is looking down a compound microscope and finds that the 

 object is not central but to the right, one brings the object to 

 the centre by pushing the slide still farther to the right. The 

 relation between muscular action and consequent visual change 

 is the reverse of the usual. The student's initial bewilderment 

 and clumsiness demonstrate that there is no neural mechanism 

 inborn and ready for the reversed relation. But after a few days' 

 practice co-ordination develops. 



These examples, and all the facts of which they are representa- 

 tive, show that the nervous system is able to develop ways of 

 behaving which are not inborn and are not specified in detail by 

 the gene-pattern. 



1/5. Learned behaviour has many characteristics, but we shall 

 be concerned chiefly with one: when animals and children learn, 

 not only does their behaviour change, but it changes usually for 

 the better. The full meaning of ' better ' will be discussed in 

 Chapter 5, but in the simpler cases the improvement is obvious 

 enough. ' The burned child dreads the fire ' : after the experi- 

 ence the child's behaviour towards the fire is not only changed, 

 but is changed to a behaviour which gives a lessened chance of 

 its being burned again. We would at once recognise as abnormal 

 any child who used its newly acquired knowledge so as to get 

 to the flames more quickly. 

 To demonstrate that learning usually changes behaviour from a 



3 



