GREAT STEPS IN EVOLUTION 93 



of stimulus, only one answer to every ques- 

 tion, but there are others whose behaviour 

 is at a higher level, illustrating what may be 

 called "jthe method of trial and error." They 

 "try" one kind of reaction after another, 

 until, in some cases, they give the effective 

 response. 



But while we cannot doubt that 



of beh^vi'mi 1 ** Qrp tn ^ fnnnH in 



. r new possibilities must have opened 



up whenever head-brains were established. 



For thift pftnt.ra,]"g.o.f tliP nprvnijfl ,syatprn 

 must hfl-Yfi meant, a. npw int.eg^flif.jftj^ a. more 

 unified control, of the whole organism. 



We cannot attempt to summarize the 

 discernible steps in the evolution of beha- 

 viour, but we wish to press home the fact that 

 what we are so familiar with to-day is the 

 long result of time. We see behaviour rising, 

 along one line, to its wonderful instinctive 

 expressions. We see it rising (whether fur- 

 ther or along another line is still under dis- 

 cussion) into_ intelligent. eyprflsajflTi ,whera 



is P ftT TreptMfrl inference. Finally, in 

 with his conceptual inferences, intel- 

 ligent -foehavioi^r becomes rflt ional conduct. 



PROGRESS ALONG MANY LINES. In his 

 interesting "Evolution of Plants," Dr. Scott 

 refers to the important fact that at a time so 

 remote as the Devonian period, when there 



