io8 THE EVOLUTION OF MAN 



non-adaptive to variation in environment. This is as true of 

 man as of animals. 



Again broadly speaking, it must be recognized that the 

 range and complexity of animal instincts bears some relation 

 to the organization of the central nervous system, but the rela- 

 tion is a highly complicated one. Certain arthropods, for 

 example, like the ant, the bee, the spider, the wasp, have amaz- 

 ingly elaborate instincts, although the pattern of the nervous 

 system is relatively simple. On the other hand, certain of the 

 mammals whose nervous system simulates that of man himself 

 are equipped with instincts of a seemingly less complicated and 

 remarkable character. Unequivocal tropisms, as might be 

 expected, are generally more striking and presumably more 

 frequent in creatures of simpler type than in those higher up 

 the scale. As is natural, instincts tend to follow patterns ap- 

 propriate to the particular environment in which the animal 

 thrives. Birds thus develop nesting instincts, which are quite 

 different in form from any correlative instincts of fishes. The 

 latter, on the other hand, develop spawning instincts, which 

 vary in some essential particulars from the reproductive in- 

 stincts of the birds and mammals. In discussing intelligence 

 it is highly essential to keep constantly in mind these inherited 

 forms of behavior and to distinguish them sharply from acts 

 acquired by the creature of its own initiative. 



With this brief background of general impressions regard- 

 ing instinctive and reflex endowment of animals, we may turn 

 attention to their more strictly intelligent behavior. At this 

 point we are thrown back on two types of evidence whose 

 relative value is estimated quite differently by different scien- 

 tists. We have, on the one hand, the observations of the out- 

 door naturalist, who undertakes to describe the behavior of 

 animals as seen under the typical conditions of nature. On 

 the other hand, we have the experimental school, which has 

 attempted to study and analyze the behavior of animals under 



