Animal Intelligence 
history means thatlthe chick, when confronted by loneliness 
and confining walls, responds by those acts which in similar 
conditions in nature would be likely to free him. | Some one 
of these acts leads him to the successful act, and the result- 
ing pleasure stamps it in. Absence of pleasure stamps all 
others ou. The case is just the same as with dogs and cats. 
The time-curves are shown in Fig. 18. 
Coming now to the question of differences in intelligence 
between the different animals, it is clear that such differ- 
ences are hard to estimate accurately. The chicks are 
surely very much slower in forming associations and less 
able to tackle hard ones, but the biggest part of the differ- 
ence between what they do and what the dogs and cats do 
is not referable so much to any difference in intelligence as to 
a difference in their bodily organs and instinctive impulses. 
As between dogs and cats, the influence of the difference 
in quantity of activity, in the direction of the instinctive 
impulses, in the versatility of the fore limb, is hard to 
separate from the influence of intelligence proper. The 
best practical tests to judge such differences in general 
would be differences in memory, which are very easily got 
at, differences in the delicacy and complexity attainable, 
and, of course, differences in the slope of the curves for the 
same association. If all these tests agreed, we should have 
a right to rank one animal above the other in a scale of 
intelligence. But this whole question of grading is, after 
all, not so important for comparative psychology as its 
popularity could lead one to think. | Comparative psy- 
chology wants first of all to trace human intellection back 
through the phylum to its origin, and in this aim is helped 
little by knowing that dogs are brighter than cats, or 
whales than seals, or horses than cows. Further, the whole 
question of ‘intelligence’ should be resolved into particular 
