ADAPTATION AS STABILITY 5/13 



The stable organism 



5/12. A most impressive characteristic of living organisms is 

 their mobility, their tendency to change. McDougall expressed 

 this characteristic well in the example of S. 5/8. Yet our 

 formulation transfers the centre of interest to the resting 

 state, to the fact that the essential variables of the adapted 

 organism change less than they would if they were unadapted. 

 Which is important : constancy or change ? 



The two aspects are not incompatible, for the constancy of some 

 variables may involve the vigorous activity of others. A good 

 thermostat reacts vigorously to a small change of temperature, 

 and the vigorous activity of some of its variables keeps the 

 others within narrow limits. The point of view taken here is 

 that the constancy of the essential variables is fundamentally 

 important, and that the activity of the other variables is impor- 

 tant only in so far as it contributes to this end. 



5/13. So far the discussion has traced the relation between the 

 concepts of ' adaptation ' and of 4 stability '. It will now be 

 proposed that ' motor co-ordination ' also has an essential con- 

 nection with stability. 



c Motor co-ordination ' is a concept well understood in physio- 

 logy, where it refers to the ability of the organism to combine the 

 activities of several muscles 

 so that the resulting move- 

 ment follows accurately its 

 appropriate path. Con- 

 trasted to it are the concepts 

 of clumsiness, tremor, ataxia, 

 athetosis. It is suggested Figure 5/13/1. 



that the presence or absence 



of co-ordination may be decided, in accordance with our methods, 

 by observing whether the movement does, or does not, deviate 

 outside given limits. 



The formulation seems to be adequate provided that we measure 

 the limb's deviations from some line which is given arbitrarily, 

 usually by a knowledge of the line followed by the normal limb. 

 A first example is given by Figure 5/13/1, which shows the line 

 traced by the point of an expert fencer's foil during a lunge. 



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