Nisms: (i) the air-conditioner; (ii) the climber’s oxygen supply; (iii) the wind-
Screen-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.
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, η, has less variety than the set
of all possible values in E; for η 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 essen-
Tial function of F as a regulator is that it shall block the transmis-
Sion of variety from disturbance to essential variable.
Since this characteristic also implies that the regulator’s func-
Tion 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
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A N I N T R O D UC T I O N T O C Y B E R NE T I C S
R EG U LA TIO N IN BI OL OG I CA L SY STEMS
Decide which to buy. I test each for a day against similar distur-
Bances and then look at the records of the temperatures; they are
As in Fig. 10/6/1:
Information about the times reaching the essential variables. In
The same way, the skilled provider for a family may go through
Difficult times without his family realising that anything unusual
Has happened. The family of an unskilled provider would have
Discovered it.
In general, then, an essential feature of the good regulator is
That it blocks the flow of variety from disturbances to essential
Variables.
The blocking may take place in a variety of ways, which
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Prove, however, on closer examination to be fundamentally the
Same. Two extreme forms will illustrate the range.
One way of blocking the flow (from the source of disturbance
D to the essential variable E) is to interpose something that acts as
A simple passive block to the disturbances. Such is the tortoise’s
Shell, which reduces a variety of impacts, blows, bites, etc. to a
Negligible disturbance of the sensitive tissues within. In the same
Class are the tree’s bark, the seal’s coat of blubber, and the human
Skull.
At the other extreme from this static defence is the defence by
Skilled counter-action— the defence that gets information about
The disturbance to come, prepares for its arrival, and then meets
The disturbance, which may be complex and mobile, with a
Defence that is equally complex and mobile. This is the defence of
The fencer, in some deadly duel, who wears no armour and who
Trusts to his skill in parrying. This is the defence used mostly by
The higher organisms, who have developed a nervous system pre-
Cisely for the carrying out of this method.
When considering this second form we should be careful to
Notice the part played by information and variety in the process.
The fencer must watch his opponent closely, and he must gain
Information in all ways possible if he is to survive. For this pur-
Pose he is born with eyes, and for this purpose he learns how to
Use them. Nevertheless, the end result of this skill, if successful,
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