5/13 ADAPTATION AS STABILITY 



started at X\ moves to A r and goes past it to X". Then x remains 

 almost constant and y changes until the representative point 

 reaches C. Then y stops changing, and x changes towards, and 

 reaches, its resting value X. The system has now reached a state 

 of equilibrium and no further changes occur. This account is just 

 a transcription into words of what the field defines graphically. 



Now the shape and features of any field depend ultimately on 

 the real physical and chemical construction of the ' machine ' 

 from which the variables are abstracted. The fact that the line 

 of behaviour does not run straight from A to R must be due to 

 some feature in the 4 machine ' such that if the machine is to 

 get from state A to state R, states B and C must be passed 

 through of necessity. Thus, if the machine contained moving 

 parts, their shapes might prohibit the direct route from A to R; 

 or if the system were chemical the prohibition might be thermo- 

 dynamic. But in either case, if the observer watched the machine 

 work, and thought it alive, he might say : ' How clever ! x 

 couldn't get from A to R directly because this bar was in the 

 way; so x went to B, which made y carry x from B to C; and 

 once at C, x could get straight back to R. I believe x shows 

 foresight.' 



Both points of view are reasonable. A stable system may be 

 regarded both as blindly obeying the laws of its nature, and also 

 as showing skill in getting back to its state of equilibrium in spite 

 of obstacles.* 



5/13. The second property is shown when an organism reacts to 

 a variable with which it is not directly in contact. Suppose, 

 for instance, that the diagram of immediate effects (S. 4/12) is 

 that of Figure 5/13/1; the variables have been divided by the 

 dotted line into ' animal ' on the right and ' environment ' on 

 the left, and the animal is not in direct contact with the variable 

 marked X. The system is assumed to be stable, i.e. to have 



* I would like to acknowledge that much of what I am describing was 

 arrived at independently by G. Sommerhoff. I met his Analytical Biology 

 only when the first edition of Design for a Brain was in proof, and I could do 

 no more than add his title to my list of references. Since then it has become 

 apparent that our work was developing in parallel, for there is a deep similarity 

 of outlook and method in the two books. The superficial reader might notice 

 some differences and think we are opposed, but I am sure the distinctions are 

 only on minor matters of definition or emphasis. The reader who wishes to 

 explore these topics further should consult his book as a valuable independent 

 contribution. 



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