94 EVOLUTION 



THE BEGINNINGS OF BEHAVIOUR. Jen- 

 nings has shown that some unicellular animals 

 " behave " in a very definite way. They are 

 not mere automata which rush about as long 

 as their spring keeps unrolling, and they are 

 more than the mere slaves of stimulus. There 

 are some, it is true, which seem to have "only 

 one kind of reaction to every kind of stimulus, 

 only one answer to every question, but there 

 are others whose behaviour is at a higher 

 level, illustrating what may be called " the 

 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 the be- 

 ginnings of behaviour are to be found in the 

 Protozoa, new possibilities must have opened 

 up whenever head-brains were established. 

 For this centralizing of the nervous system 

 must have meant a new integration, a more 

 unified control, of the whole organism. 



We cannot attempt to summarize the 

 discernible steps in the evolution of behaviour, 

 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 expres- 

 sions. We see it rising (whether further or 

 along another line is still under discussion) 



