REGULATION IN BIOLOGICAL SYSTEMS 10/6 



regulatory machinery. F, by its action, tends to lessen the effect 

 of D on E. 



(2) The automatic pilot. £" is a vector with three components — 

 yaw, pitch, and roll — and iq is the set of positions in which these 

 three are all within certain limits. D is the set of disturbances that 

 may affect these variables, such as gusts of wind, movements of the 

 passengers in the plane, and irregularities in the thrusts of the engines. 

 Fis the whole machinery — pilot, ailerons, rudder, etc. — whose action 

 determines how D shall affect E. 



(3) The bicycle rider. E is chiefly his angle with the vertical. 

 ■q is the set of small permissible deviations. D is the set of those 

 disturbances that threaten to make the deviation become large. F 

 is the whole machinery^ — mechanical, anatomical, neuronic — that 

 determines what the effect of D is on E. 



Many other examples will occur later. Meanwhile we can sum- 

 marise by saying that natural selection favours those gene-patterns 

 that get, in whatever way, a regulator F between the disturbances D 

 and the essential variables E. Other things being equal, the better F 

 is as a regulator, the larger the organism's chance of survival. 



Ex. : What variables are kept within limits by the following regulatory mech- 

 anisms: (i) the air-conditioner; (ii) the climber's oxygen supply; (iii) the 

 windscreen-wiper; (iv) the headlights of a car; (v) the kitchen refrigerator; 

 (vi) the phototaxic plant; (vii) sun-glasses; (viii) the flexion reflex (a quick 

 lifting of the foot evoked by treading on a sharp stone) ; (ix) blinking when 

 an object approaches the eye quickly ; (x) predictor for anti-aircraft gunfire. 



10/6. Regulation blocks the flow of variety. On what scale can 

 any particular mechanism F be measured for its value or success 

 as a regulator? The perfect thermostat would be one that, in spite 

 of disturbance, kept the temperature constant at the desired level. 

 In general, there are two characteristics required: the maintenance 

 of the temperature within close limits, and the correspondence of 

 this range with the desired one. What we must notice in particular 

 is that the set of permissible values, 17, has less variety than the set 

 of all possible values in E; for 17 is some set selected from the states 

 of E. If F is a regulator, the insertion of F between D and E lessens 

 the variety that is transmitted from D to E. Thus an essential 

 function of Fas a regulator is that it shall block the transmission of 

 variety from disturbance to essential variable. 



Since this characteristic also implies that the regulator's function 

 is to block the flow of information, let us look at the thesis more 

 closely to see whether it is reasonable. 



Suppose that two water-baths are offered me, and I want to decide 



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