THE EVOLUTION OF INTELLIGENCE 119 



the elephant brushing off flies with a branch held in his trunk, 

 or the alleged instances of monkeys using stones to crack nuts, 

 are but sporadic examples of probably accidental achievements 

 which in no case lead on to any general ability to make use of 

 utensils in a discriminating way. One must not, in this con- 

 nection, confuse with intelligent actions the remarkable in- 

 stinctive manipulations which many animals are capable of, 

 nor the tricks which they may have been taught by long and 

 painful effort. The elaborate nests which many birds build are 

 amazing instances of utilizing the most varied materials in 

 highly complicated forms. Similarly, the beavers accomplish 

 the most astonishing results with the materials which they 

 employ and there are abundant reports of their adaptability 

 to changing conditions which, if well established, are certainly 

 suggestive of highly intelligent reactions. Here again, how- 

 ever, the experimental zoologist who has studied most care- 

 fully the instinctive activities of animals will be most hesitant 

 to ascribe individual intelligence comparable to that of man 

 in interpretation of these animal reactions. Certain it is that, 

 generally speaking, the primates are much more skillful than 

 other animals in adapting themselves to shifting conditions 

 and that, even among them, the evidence of anything compa- 

 rable with a human process of inference, or a process of ab- 

 stracting, or of generalizing, is very, very slight. In any case, 

 the issue which is raised here again must be clearly understood, 

 to wit, that beyond the adjustments which are innate, inherited, 

 and unlearned by the individual are those which represent his 

 individual acquirement independent of such inherited tend- 

 encies. The latter is the field of individual intelligence. 



As was indicated earlier in this paper, there is a wide gen- 

 eral correspondence between the degree of intelligence mani- 

 fested by animal forms and the structure of the nervous system. 

 In particular, intelligence in its narrower and more specific 

 sense, as distinguished from instinct, appears to be rather a 



