Inquiry Into Inquiry

Requisite Variety

11/1.   In the previous chapter we considered regulation from the biological point of view, taking it as something sufficiently well understood.  In this chapter we shall examine the process of regulation itself, with the aim of finding out exactly what is involved and implied.  In particular we shall develop ways of measuring the amount or degree of regulation achieved, and we shall show that this amount has an upper limit.

11/2.   The subject of regulation is very wide in its applications, covering as it does most of the activities in physiology, sociology, ecology, economics, and much of the activities in almost every branch of science and life.  Further, the types of regulator that exist are almost bewildering in their variety.  One way of treating the subject would be to deal seriatim with the various types;  and chapter 12 will, in fact, indicate them.  In this chapter, however, we shall be attempting to get at the core of the subject — to find what is common to all.

What is common to all regulators, however, is not, at first sight, much like any particular form.  We will therefore start anew in the next section, making no explicit reference to what has gone before.  Only after the new subject has been sufficiently developed will we begin to consider any relation it may have to regulation.

Regulation In Biological Systems

Survival

10/7.[concl.]   When considering this second form [of defence] 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 purpose he is born with eyes, and for this purpose he learns how to use them.  Nevertheless, the end result of this skill, if successful, is shown by his essential variables, such as his blood-volume, remaining within normal limits, much as if the duel had not occurred.  Information flows freely to the non-essential variables, but the variety in the distinction “duel or no-duel” has been prevented from reaching the essential variables.

Through the remaining chapters we shall be considering this type of active defence, asking such questions as:  what principles must govern it?  What mechanisms can achieve it?  And, what is to be done when the regulation is very difficult?

Regulation In Biological Systems

Survival

10/6.[concl.]   In general, then, an essential feature of the good regulator is that it blocks the flow of variety from disturbances to essential variables.

10/7.   The blocking may take place in a variety of ways, which 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 to the essential variable 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 precisely for the carrying out of this method.