THE UNIQUENESS OF THE INDIVIDUAL 



endosomatic senses, and motor instruments are functional, and 

 functionally intelligible, only when they are used. It is not 

 spectacles, but spectacles worn and looked through, that are 

 instruments of vision, and the hammer is only a tool when it is 

 wielded by the hand. (I think it was Wilfred Trotter who said 

 that when a surgeon uses a simple instrument like a probe or 

 seeker, which is merely an extension of the fingers as stilts are 

 extensions of legs, he actually refers the sense of touch to its 

 tip.) The relationship between instrument and user may be 

 very remote, as it is with guided missiles and with engines 

 designed to work without attention, but their conduct is built 

 into them by human design and, in principle, their functional 

 integration with the user is just the same. It is for this reason 

 I deplore the habit of describing the brain as a kind of calcul- 

 ating machine; the truth is that a calculating machine is a kind 

 of exosomatic brain. It performs brain-like functions, much as 

 cameras have eye-like and clothes have skin-like functions, and 

 motor-cars the functions endosomatically performed by legs. 

 We may indeed learn something about the brain by studying 

 calculating machines, as we have learned something about the 

 eye by studying lenses; but it need not be so: the internal- 

 combustion engine has no lessons to teach us about how 

 muscles work. 



Biologists in the nineteenth century were much impressed by 

 the fact that exosomatic instruments undergo a systematic 

 secular change that is somewhat analogous to ordinary bio- 

 logical evolution. Just as legs and ears have changed in the 

 course of time, so also have bicycles, microscopes, radio sets 

 and cars. The evolution of both endosomatic and exosomatic 

 organs is gradual in synoptic view, but somewhat discontinuous 

 on closer inspection. Novelties arise in both, not in the entire 

 population but in a limited number of its members, and may or 

 may not spread thereafter through the whole. Both modes of 

 evolution are "integrative"' in the sense that they start or pro- 



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