122 HUMAN BIOLOGY 



trials, more or less obviously ineffective and wasteful, 

 eventually leads to skillful manipulation of the bottle 

 and the drinking of its contents. 



By comparing the typical performances of human infants 

 at various ages and of representatives of the various classes 

 of primate in like situations, we discover that adaptation by 

 trial and error, in other words bhndly or without insight, is 

 characteristic of all ages and types, but that the quickness of 

 adaptation on the basis of blind trial, and also the prob- 

 ability of indication of insight, tend to increase as develop- 

 ment progresses and also as we progress from the more 

 primitive toward the less primitive primate type. 



(b) Insight. The use of objects as instruments in con- 

 nection with behavioral adaptation is peculiarly significant 

 of insight. Such ability is virtually unknown in the lemurs 

 and tarsiers, so far as one may infer from observational 

 report. It appears in the monkeys, and is obviously more 

 varied and important in the anthropoid apes and in man. 

 The monkey may use a stick to draw within reach objects 

 which are not otherwise obtainable. But when the objective 

 is so placed that the stick must be used to push, direct 

 and pull it around an obstacle through a devious course 

 which sometimes tends away from and again toward the 

 subject, the monkey fails utterly, whereas the ape may 

 succeed. Herein we discover a contrast, if not a transition. 

 Insightless and persistent trial and error may ultimately 

 result in success, whatever the type of primate in question. 

 But ordinarily it is not difficult for the observer to dis- 

 tinguish between blind trial and that which is guided by 

 perception of relation of means to end and of the desired 

 object to the waiting hand of the animal. To the human 

 adult this problem of a roundabout course seems extremely 

 simple; its solution is grasped instantly. But for the infant it 

 is a real problem which prior to a certain stage of develop- 

 ment, attained only after several months, is utterly insolu- 

 ble. Ability to handle a stick deftly and to direct it toward 

 an objective does not assure success: there must in addition 

 be a measure of insight into spatial relations, and the sub- 

 ject must be able to translate its perceptual experience and 

 its insight into adaptive activity. 



