5/9 ADAPTATION AS STABILITY 



external forces acting upon it. This is true for an ordinary 

 stone just as much as for the most complex substances; and 

 its truth should be recognised also for the animal organism. 

 Being a definite circumscribed material system, it can only 

 continue to exist so long as it is in continuous equilibrium 

 with the. forces external to it: so soon as this equilibrium 

 is seriously disturbed the organism will cease to exist as the 

 entity it was.' 



(Pavlov.) 



McDougall never used the concept of ' stability ' explicitly, but 

 when describing the type of behaviour which he considered to 

 be most characteristic of the living organism, he wrote: 



4 Take a billard ball from the pocket and place it upon the 

 table. It remains at rest, and would continue to remain so 

 for an indefinitely long time, if no forces were applied to it. 

 Push it in any direction, and its movement in that direction 

 persists until its momentum is exhausted, or until it is 

 deflected by the resistance of the cushion and follows a new 

 path mechanically determined. . . . Now contrast with this 

 an instance of behaviour. Take a timid animal such as a 

 guinea-pig from its hole or nest, and put it upon the grass 

 plot. Instead of remaining at rest, it runs back to its hole; 

 push it in any other direction, and, as soon as you withdraw 

 your hand, it turns back towards its hole ; place any obstacle 

 in its way, and it seeks to circumvent or surmount it, rest- 

 lessly persisting until it achieves its end or until its energy 

 is exhausted.' 



He could hardly have chosen an example showing more clearly 

 the features of stability. 



Survival 



5/9. Are there aspects of ' adaptation ' not included within the 

 definition of ' stability ' ? Is ' survival ' to be the sole criterion 

 of adaptation ? Is it to be maintained that the Roman soldier 

 who killed Archimedes in Syracuse was better ' adapted ' in his 

 behaviour than Archimedes ? 



The question is not easily answered. It is similar to that of 

 S. 3/4 where it was asked whether all the qualities of the living 

 organism could be represented by number; and the answer must 

 be similar. It is assumed that we are dealing primarily with 

 the simpler rather than with the more complex creatures, though 



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