64 Animal Intelligence 



history means that the 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 out. 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 



