DEVELOPMENT OF BEHAVIOR 319 



vide for its own development. Through the principle of the production 

 of varied movements, and that of the resolution of one physiological 

 state into another, anything that is possible is tried, and anything that 

 turns out to be advantageous to the organism is held and made permanent. 



Thus through development in accordance with the two principles 

 mentioned, the organism comes to react no longer by trial, — by the over- 

 production of movements, — but by a single fixed response, appropriate 

 to the occasion. This is, of course, a great advantage, so long as the 

 conditions remain such as to make the response appropriate. Such 

 fixed responses are the general rule in the adult behavior of higher or- 

 ganisms, and are found to a certain extent in all organisms. In the 

 higher organisms we speak of some of these fixed responses as reflexes, 

 tropisms, habits, and instincts. The methods which we have discussed 

 are not the only possibilities for the development of such responses ; other 

 methods we shall take up later. 



After the responses of the organism have become fixed, conditions 

 may so change that these responses are no longer appropriate. The 

 organism is then in a less advantageous position than one whose behavior 

 is determined more purely by trial movements. There will be now a 

 tendency for the fixed responses to become broken up and for processes 

 of trial to supplant them, until new fixed responses, appropriate to present 

 conditions, are produced. But in many cases the fixed responses are 

 so firmly established as not to give way save after long experience of 

 their lack of efficiency, and often the organism is destroyed by the new 

 environment, before it has developed appropriate responses by which 

 to preserve itself. 



(5) We have thus far considered primarily the methods by which 

 the behavior of a given individual may be modified and made more 

 effective. It needs to be recalled that differences between the behavior 

 of different individuals may appear from other reasons. There are 

 congenital variations among different organisms. Some have naturally 

 a greater delicacy of perception or discrimination than others. Some 

 move more rapidly or in more or less varied ways than others, giving 

 some a more efficient method of reaction without any modification 

 through experience. These congenital variations play a most important 

 part in the question next to be considered. 



(6) Our discussion thus far has related to individuals. The further 

 question arises as to how modifications of behavior may arise in the race 

 as a whole. How does it happen that the behavior of the race becomes 

 changed in the same way as that of the individual, so that succeeding 

 generations show the new method of reacting without acquiring it for 

 themselves ? 



