CHAPTER 5 



Adaptation as Stability 



5/1. The concept of ' adaptation ' has so far been used without 

 definition; this vagueness must be corrected. Not only must 

 the definition be precise, but it must, by S. 2/10, be given in terms 

 that can be reduced wholly to primary operations. 



5/2. The suggestion that an animal's behaviour is ' adaptive ' 

 if the animal 4 responds correctly to a stimulus ' may be rejected 

 at once. First, it presupposes an action by an experimenter and 

 therefore cannot be applied when the free-living organism and 

 its environment affect each other reciprocally. Secondly, the 

 definition provides no meaning for ' correctly ' unless it means 

 4 conforming to what the experimenter thinks the animal ought 

 to do '. Such a definition is useless. 



Homeostasis 



5/3. I propose the definition that a form of behaviour is adaptive 

 if it maintains the essential variables (S. 3/14) within physiological 

 limits. The full justification of such a definition would involve 

 its comparison with all the known facts — an impossibly large 

 task. Nevertheless it is fundamental in this subject and I must 

 discuss it sufficiently to show how fundamental it is and how 

 wide is its applicability. 



First I shall outline the facts underlying Cannon's concept of 

 1 homeostasis '. They are not directly relevant to the problem 

 of learning, for the mechanisms are inborn; but the mechanisms 

 are so clear and well known that they provide an ideal basic 

 illustration. They show that: 



(1) Each mechanism is c adapted ' to its end. 



(2) Its end is the maintenance of the values of some essential 



variables within physiological limits. 



(3) Almost all the behaviour of an animal's vegetative system 



is due to such mechanisms. 

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