33^ BRAINS OF RATS AND MEN 



reflex, instinct — which in general are good for the 

 organism exhibiting them. It is easy, therefore, to see 

 why these tendencies are the strongest kind of inter- 

 nally determined impulsions. The impulse, not being 

 intelligently directed, persists even when in a particu- 

 lar case it may be harmful, as seen when the moth 

 repeatedly sears its wings in the flame. 



These impulsions are coeval with life, and they 

 have persisted throughout the entire course of organic 

 evolution. They face backward in that they have 

 been shaped by biological agencies, such as natural 

 selection during the previous evolutionary history of 

 the species, or by habit during the individual life. 

 They face forward in that they are adaptive or di- 

 rected (in general) toward some useful end, to wit, the 

 welfare of the individual or the species. 



Reflex behavior in any particular instance is, ac- 

 cordingly, the result of some adequate stimulus act- 

 ing upon an internal organization which has been so 

 fabricated during its own past history as to prede- 

 termine the nature of the ensuing reaction. The 

 stable pattern of the internal structure at the moment 

 is, therefore, a causative factor in determining the 

 dynamic pattern of the behavior. It is not a mystic 

 "force" (Warren, 1923). 



This primitive sort of impulse is an expression of a 

 definite trend or "set" of behavior patterns in modes 

 which have been established and stabilized in pre- 

 vious racial and individual experience and which, 



