THE DEVELOPMENT OF BIOLOGICAL CYBERNETICS

I watched a kestrel from a building high on the Citadel overlooking Plymouth Sound. It hovered at arms' length from the window in a stiff breeze, holding its position for long periods so perfectly that one could not detect the slightest movement of its head. To maintain this static hover, its wings beat quickly, varying a little in frequency and angle to adjust to the buffeting breeze, as it watched intently for any movement of prey on the ground below. It reminded me of Gerard Manley Hopkins' lines from his poem The Windhover: ‘how he rung upon the rein of a wimpling wing’. Occasionally the bird sheared away: ‘then off, off forth on swing’; to return again and take up its position as before, as if to dispel any doubts I might still have of its control in the air. ‘The achieve of, the mastery of the thing!’

In the same way our control systems master the continuous variation in the environment in which we live, holding steady a host of different internal processes against the continuous fluctuation of external change.