Regulator R very much smaller (a common case in biology), the
Law of Requisite Variety is Likely to play a dominating part. Its
Importance is that, if R is fixed in its channel capacity, the law
Places an absolute limit to the amount of regulation (or control)
That can be achieved by R, no matter how R is re-arranged inter-
Nally, or how great the opportunity in T. Thus the ecologist, if his
Capacity as a channel is unchangeable, may be able at best only to
Achieve a fraction of what he would like to do. This fraction may
Be disposed in various ways — he may decide to control outbreaks
Rather than extensions, or virus infections rather than bacillary—
But the quantity of control that he can exert is still bounded. So too
The economist may have to decide to what aspect he shall devote
His powers, and the psychotherapist may have to decide what
Symptoms shall be neglected and what controlled.
The change in the point of view suggested here is not unlike that
Introduced into statistics by the work of Sir Ronald Fisher. Before
Him, it was taken for granted that, however clever the statistician,
A cleverer could get more information out of the data. Then he
Showed that any given extraction of information had a maximum,
And that the statistician’s duty was simply to get near the maxi-
Mum— beyond that no man could go. Similarly, before Shan-
Non’s work it was thought that any channel, with a little more
Skill, could be modified to carry a little more information. He
Showed that the engineer’s duty is to get reasonably near the max-
Imum, for beyond it no-one can go. The law of Requisite Variety
Enforces a similar strategy on the would-be regulator and control-
Ler: he should try to get near his maximum— beyond that he can-
Not go. Let us therefore approach the very large system with no
Extravagant ideas of what is achievable.
245
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
RE GU LA TI N G TH E V ER Y LA R GE SY STE M
Before we proceed we should notice that when the system is
Very large the distinction between D, the source of the distur-
Bances, and T, the system that yields the outcome, may be some-
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What vague, in the sense that the boundary can often be drawn in
A variety of ways that are equally satisfactory.
This flexibility is particularly well-marked among the systems
That occur on this earth (for the terrestrial systems tend markedly
To have certain general characteristics). On this earth, the whole
Dynamic biological and ecological system tends to consist of
Many subsystems loosely coupled (S.4/20); and the sub-systems
Themselves tend to consist of yet smaller systems, again more
Closely coupled internally yet less closely coupled between one
Another; and so on. Thus in a herd of cattle, the coupling between
Members is much looser than the couplings within one member
And between its parts (e.g. between its four limbs); and the four
Limbs are not coupled as closely to one another as are the mole-
Cules within one bone. Thus if some portion of the totality is
Marked out as T, the chief source D of disturbance is often other
Systems that are loosely coupled to T, and often sufficiently sim-
Ilar to those in T that they might equally reasonably have been
Included in it. In the discussion that follows, through the rest of
The book, this fact must be borne in mind: that sometimes an
Equally reasonable demarcation of T and D might have drawn the
Boundary differently, without the final conclusions being affected
Significantly. Arbitrary or not, however, some boundary must
Always be drawn, at least in practical scientific work, for other-
Wise no definite statement can be made.
When the system T is very large— when the organism as
Regulator faces a very large and complex environment with lim-
Ited resources— there are various ways that may make regulation
Possible. (If regulation is not possible, the organism perishes— an
Extremely common outcome that must not be forgotten; but this
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Case needs no detailed consideration.)
Sometimes regulation may be made possible by a re-defining of
What is to be regarded as acceptable— by a lowering of standards.
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