ANIMAL AND RATIONAL INTELLIGENCE 213 



come to trace them in outline. But, dealing here 

 with questions of comparative intelligence, it is 

 obvious that we must restrict our definition of 

 intelligence to its simplest phase. Only on this 

 condition do we find common exercise in the life of 

 animals and of men, to be attributed to common power, 

 which we name mental power, or intelligence, in 

 contrast with physical power, appearing in a sensori- 

 motor system common to all organic life. Allowing 

 for the facts on which we conclude that there are in 

 the life of the higher mammals manifestations of 

 intelligence, amounting in some cases to distinct acts 

 of reasoning, l these, taken at their highest valuation, 

 are much beneath what we mean by the powers of a 

 rational life. So great is this contrast, that the 

 difference between the brain of the ape, or of the 

 dog, and the human brain, great as it is, is insig 

 nificant in comparison with the distance which 

 separates the lives of these animals from the life of 

 the ordinary man, even if uncivilised man be taken 

 as our standard of human capability. 



Evidence fails when we look for independent action 

 of Intelligence in animals. We do not find any of 

 them in their natural state rise above interpretation 

 of signs : we do not see in their history, accumulation 

 of knowledge for its own sake. In their use of means 

 for attainment of ends naturally desired by them, we 

 do not find them capable of any considerable adapta 

 tion, such as would obviate difficulties, still less such 

 as would increase facilities. Even when, after long 

 training, an animal has been brought to render great 

 service by its aptitude, or to perform surprising feats, 

 1 Wallace s Darwinism, p. 426. 



