280 Animal Intelligence 



Paramecium by Stevenson Smith are easily forgotten learn- 

 ings or long retained excitabilities. Sooner or later clear 

 learning appears, and then, from crabs to fish and turtle, 

 from these to various birds and mammals, from these to 

 monkeys, and from these to man, a fairly certain increase 

 in sheer ability to learn, in the potency of a supposedly 

 constant degree of satisfyingness or annoyingness to influ- 

 ence the connection preceding it, can be assumed. We 

 cannot, of course, define just what we mean by equal satis- 

 fyingness to a mouse and a man, but the argument is sub- 

 stantially the same as that whereby we assume that the 

 gifted boy has more sheer ability to learn than the idiot, so 

 that if the two made the same response to the same situa- 

 tion and were equally satisfied thereby, the former would 

 form the habit more firmly. 



We may, therefore, expect that when knowledge of the 

 structure and behavior of the neurones comprising the con- 

 nection-systems of animals (or of the neurones' predecessors 

 in this function) progresses far enough to inform us of just 

 what happens when a connection is made stronger or weaker 

 and of just what effects satisfying and annoying states of 

 affairs exert upon the connection-system (and in particular 

 upon the connections most recently in activity) the ability 

 to learn will show as true an evolution as the ability to sneeze, 

 oppose the thumb, or clasp an object touched by the hand. 



If my analysis is true, the evolution of behavior is a rather 

 simple matter. Formally the crab, fish, turtle, dog, cat, 

 monkey and baby have very similar intellects and charac- 

 ters. All are systems of connections subject to change by 

 the law of exercise and effect. The differences are : first, in 

 the concrete particular connections, in what stimulates the 

 animal to response, what responses it makes, which stimulus 

 connects with which response, and second, in the degree of 



