tradition: the evidence of biology 



using animal. The instruments used by human beings are of 

 two chief kinds. The first I shall call motor or effector instru- 

 ments — for example, hammers, cutlery, motor-cars, mega- 

 phones and guns, instruments which increase, sometimes 

 prodigiously, our repertoire of motor activity. Instruments of 

 the second kind can be described as sensory accessories: 

 spectacles, ear-trumpets, radio sets, thermometers, appliances 

 which increase beyond all former bounds the competence of 

 one''s ordinary senses. (Not all instruments fall into these two 

 categories: clothes, for example, do not.) Man is not quite 

 uniquely an instrument-using animal; but the odd examples of 

 the use of tools by lower animals are so rare that each one is 

 treasured and made a fuss of. The Galapagos woodpecker, a 

 sort of finch, uses a thorn held in its beak to prise insects from 

 the bark of trees. Many animals make houses or shelters, 

 but these are tools of a kind I shall not be concerned with 

 here. 



I propose to use the terms invented by the great actuary 

 A. J. Lotka to distinguish between the organs that we are born 

 with and organs that are made: e?idosomatic instruments for 

 eyes, claws, wings, teeth and kidneys, exosomatic instruments 

 for telescopes, toothpicks, scalpels, balances and clothes. 

 Although there is a very obvious distinction between instru- 

 ments of these two kinds, the distinction is much less obvious 

 biologically than it is to the unaided power of common sense. 

 The two kinds of instrument serve the same biological func- 

 tions, and each can to some extent deputize for the other. Even 

 in a quite narrowly biological sense, man is a flying animal: he 

 can fly faster, farther and higher than birds, if not yet with 

 quite the same finesse. It is also important to remember that 

 exosomatic instruments Sive functionally parts of the body, even 

 if they are anatomically separate and distinct. All sensory tools 

 like spectacles, Geiger counters and spectrophotometers report 

 back at some stage and by some route through the ordinary 



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