5/6 DESIGN FOR A BRAIN 



at first the kitten's behaviour was not homeostatic for skin 

 temperature, it has now become so. Such behaviour is ' adapted ' : 

 it preserves the life of the animal by keeping the essential variables 

 within limits. 



The same thesis can be applied to a great deal, if not all, of 

 the normal human adult's behaviour. In order to demonstrate 

 the wide application of this thesis, and in order to show that 

 even Man's civilised life is not exceptional, some of the surround- 

 ings which he has provided for himself will be examined for their 

 known physical and physiological effects. It will be shown that 

 each item acts so as to narrow the range of variation of his 

 essential variables. 



The first requirement of a civilised man is a house ; and its 

 first effect is to keep the air in which he lives at a more equable 

 temperature. The roof keeps his skin at a more constant dryness. 

 The windows, if open in summer and closed in winter, assist in 

 the maintenance of an even temperature, and so do fires and 

 stoves. The glass in the windows keeps the illumination of the 

 rooms nearer the optimum, and artificial lighting has the same 

 effect. The chimneys keep the amount of irritating smoke in 

 the rooms near the optimum, which is zero. 



Many of the other conveniences of civilisation could, with little 

 difficulty, be shown to be similarly variation-limiting. An attempt 

 to demonstrate them all would be interminable. But to confirm 

 the argument we will examine a motor-car, part by part, in 

 order to show its homeostatic relation to man. 



Travel in a vehicle, as contrasted with travel on foot, keeps 

 several essential variables within narrower limits. The fatigue 

 induced by walking for a long distance implies that some vari- 

 ables, as yet not clearly known, have exceeded limits not trans- 

 gressed when the subject is carried in a vehicle. The reserves 

 of food in the body will be less depleted, the skin on the soles 

 of the feet will be less chafed, the muscles will have endured 

 less strain, in winter the body will have been less chilled, and 

 in summer it will have been less heated, than would have hap- 

 pened had the subject travelled on foot. 



When examined in more detail, many ways are found in which 

 it serves us by maintaining our essential variables within narrower 

 limits. The roof maintains our skin at a constant dryness. The 

 windows protect us from a cold wind, and if open in summer, 



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