Ex. 3: What would be an appropriate definition of “lethal”, if C’s attack were
Invariably fatal to M?
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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
What is it survives, over the ages ? Not the individual organ-
Ism, but certain peculiarly well compounded gene-patterns, par-
Ticularly those that lead to the production of an individual that
Carries the gene-pattern well protected within itself, and that,
Within the span of one generation, can look after itself.
What this means is that those gene-patterns are specially likely
To survive (and therefore to exist today) that cause to grow,
Between themselves and the dangerous world, some more or less
Elaborate mechanism for defence. So the genes in Testudo cause
The growth of a shell; and the genes in Homo cause the growth of
A brain. (The genes that did not cause such growths have long
Since been eliminated.)
Now regard the system as one of parts in communication. In the
Previous section the diagram of immediate effects (of cat and
Mouse) was (or could be regarded as)
C → M
We are now considering the case in which the diagram is
D → F → E
In which E is the set of essential variables, D is the source of dis-
Turbance and dangers (such as C) from the rest of the world, and
F is the interpolated part (shell, brain, etc.) formed by the gene-
Pattern for the protection of E. (F may also include such parts of
The environment as may similarly be used for E’s protection—
Burrow for rabbit, shell for hermit-crab, pike for pike-man, and
Sword (as defence) for swordsman.)
For convenience in reference throughout Part III, let the states
of the essential variables E be divided into a set η ∇ those that cor-
respond to “organism living” or “good”— and not- η ∇ those that
Correspond to “organism not living” or “bad”. (Often the classifi-
Cation cannot be as simple as this, but no difficulty will occur in
Principle; nothing to be said excludes the possibility of a finer
Classification.)
To make the assumptions clear, here are some simple cases, as
Illustration. (Inanimate regulatory systems are given first for sim-
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Plicity.)
The thermostatically-controlled water-bath. E is its temper-
ature, and what is desired ( η) is the temperature range between,
say 36 ° and 37 °C. D is the set of all the disturbances that may
Drive the temperature outside that range— addition of cold water,
Cold draughts blowing, immersion of cold objects, etc. F is the
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Whole regulatory machinery. F, by its action, tends to lessen the
Effect of D on E.
The automatic pilot. E is a vector with three components—
yaw, pitch, and roll— and η 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. F is the whole machinery— pilot, ailerons, rudder, etc.—
Whose action determines how D shall affect E.
The bicycle rider. E is chiefly his angle with the vertical. ,1
Is the set of small permissible deviations. D is the set of those dis-
Turbances 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-pat-
Terns 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 mecha-
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