Homeostasis

Homeostasis is the maintenance of a stable internal state in a changing environment. Body temperature, blood pressure, blood sugar and the balance of salts in the blood are all held within narrow ranges by networks of sensors and corrective responses.

Origins

The French physiologist Claude Bernard observed in the nineteenth century that the stability of the milieu intérieur, the internal environment, is the condition for free and independent life. The American physiologist Walter Cannon named the process “homeostasis” in 1926 and described it in The Wisdom of the Body (1932). His student Arturo Rosenblueth carried the idea into the founding of cybernetics.

In cybernetics

Homeostasis is negative feedback in living form, and cybernetics treated it as a general principle. W. Ross Ashby’s homeostat (1948) was a machine built to demonstrate it, and his idea of essential variables (the quantities a system must keep within limits to survive) gave the concept a precise form. Stafford Beer applied it to organisations, and James Lovelock and Lynn Margulis to the whole planet in the Gaia hypothesis.

Later thinkers have stressed that living systems also anticipate. Allostasis describes regulation through prediction, changing set points in advance of need, an idea close to Karl Friston’s free energy principle.

Further reading

• Walter Cannon, The Wisdom of the Body (1932)
• W. Ross Ashby, Design for a Brain (1952)