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 mania fairly certain increase 
in sheer ability to learn, i 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 arinoying 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 
