Tuesday, May 27, 2008


"HOMEODYNAMICS - One of the dominating motifs in biological thinking was provided by the physiologist Claude Bernard in Paris in the 1850s. Bernard, who among many other discoveries carried out some of the earliest systematic studies on what were later to become known as enzymes and hormones, saw living systems as explicable neither by vitalism (the belief that there existed some special 'life forces' beyond the reach of chemistry or physics) nor by mechanism. "He regarded stability as a major organising physiological principle, and emphasised the constancy of what he described as the milieu interieur - the 'internal environment' - of multicellular organisms, their tendency to work to regulate this environment in terms of temperature, acidity, ionic composition and so forth.

This capacity he saw as providing a stable context in which the individual cells of the body can function with a minimum of disruptive turmoil. "Seventy years later the American physiologist Walter Cannon generalzed Bernard's concept by introducing the term homeostasis - the tendency of a regulated system to maintain itself close to some fixed point, like the temperature of a room controlled by a central heating system and a thermostat. No modern textbook account of physiological or psychological mechanisms fails to locate itself within this homeostatic metaphor. But the metaphor of homeostasis contrains our view of living systems. "Lifelines are not purely homeostatic: they have a beginning at conception, and an end at death. Organisms, and indeed ecosystems, develop, mature and age.

The set oints of homeostatic theory are not themselves constant during this trajectory but change over time. The organism switches its own thermostat. Organisms are active players in their own fate, not simply the playthings of the gods, nature or the inevitable workings-out of replicator-driven natural selection. To understand lifelines, therefore, we need to replace homeostasis with a richer concept, that of homeodynamics."

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