CHAPTER XIX 

 DEVELOPMENT OF BEHAVIOR 



It is not the primary purpose of the present work to treat the problems 

 of development, but rather to give an analysis of behavior as we now find 

 it. But the results of this analysis furnish a certain amount of evidence 

 as to how development may have occurred; this it will be well to set 

 forth briefly. We shall consider first the development of behavior in 

 the individual, then its development in the race. In unicellular organ- 

 isms the first, perhaps, includes the second. 



The primary facts for development in behavior are two principles 

 to which our analysis of the chief factors in behavior have led us. One 

 of these is that behavior is based fundamentally on the selection of varied 

 movements. The other is the law in accordance with which the resolu- 

 tion of one physiological state into another becomes readier and more 

 rapid through repetition. 



In making use of the law of the readier resolution of physiological 

 states after repetition in the study of development, it needs to be kept 

 in mind that this law has been rigidly demonstrated for the lower organ- 

 isms only in scattered instances. It has been shown to be valid in cer- 

 tain unicellular organisms, but in these cases it has not been shown that 

 the modifications induced are lasting, as must be the case if this law plays 

 a part in the development of behavior. In the lowest metazoa the law 

 has Hkewise been demonstrated only for a few cases. In the flatworm 

 and the Crustacea we find the law clearly exhibited in the form that is 

 necessary in order that it may play a part in the permanent modification 

 of behavior. 



On the other hand, the fact that the law remains undemonstrated 

 for many of the lowest organisms by no means indicates that it is not here, 

 valid. We lack proper experiments to show whether it exists or not. 

 It is exceedingly difficult to carry out experiments that shall actually 

 test this matter in the lowest animals. The view that this law is univer- 

 sally valid in organic behavior is thoroughly consistent with all that we 

 know of the behavior of lower organisms, and the fact that it has actually 

 been demonstrated in certain cases favorable for experimentation in 

 unicellular organisms raises a presumption of its general validity. The 



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