## Regulation In Biological Systems

### Survival

10/5.[concl.]   To make the assumptions clear, here are some simple cases, as illustration.  (Inanimate regulatory systems are given first for simplicity.)

(1) The thermostatically-controlled water-bath.  $E$ is its temperature, and what is desired $(\eta)$ 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 whole regulatory machinery.  $F,$ by its action, tends to lessen the effect of $D$ on $E.$

(2) The automatic pilot.  $E$ is a vector with three components — yaw, pitch, and roll — and $\eta$ 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 $E.$

(3) The bicycle rider.  $E$ is chiefly his angle with the vertical.  $\eta$ 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 summarise 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.

### Reference

• Ashby, W.R. (1956), An Introduction to Cybernetics, Chapman and Hall, London, UK.  Republished by Methuen and Company, London, UK, 1964.  Online.

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