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.  is its temperature, and what is desired is the temperature range between, say 36° and 37°C.  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.  is the whole regulatory machinery.  by its action, tends to lessen the effect of on

(2) The automatic pilot.  is a vector with three components — yaw, pitch, and roll — and is the set of positions in which these three are all within certain limits.  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.  is the whole machinery — pilot, ailerons, rudder, etc. — whose action determines how shall affect

(3) The bicycle rider.  is chiefly his angle with the vertical.  is the set of small permissible deviations.  is the set of those disturbances that threaten to make the deviation become large.  is the whole machinery — mechanical, anatomical, neuronic — that determines what the effect of is on

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 between the disturbances and the essential variables   Other things being equal, the better is as a regulator, the larger the organism’s chance of survival.