2 min read


Simulating homeostasis

James Lovelock's Daisyworld is a computer model of Gaia's homeostatic regulation of planetary climate. It features a coupled interaction between an idealized biota and its environment. Like our world, Daisyworld is steadily forced by a sun gradually gaining in strength. However, Daisyworld's biota consisted of only two species--black daisies that thrive when it’s cool and white daisies that thrive when it’s hot. Seeded with both, Daisyworld starts out cool but is gradually heated by a warming sun. Yet due to their different albedos, or indexes of reflectivity, the black and white daisies feed back upon that global warming to different effect.

The low-albedo black daisies heat the planet further by absorbing the sun’s rays, while the high-albedo white daisies cool the planet by reflecting that same radiation back to space. The black daisies thrive at first under the initially cool conditions that suppress the growth of the white daisies. But as the black daisies proliferate, the planet warms up enough to favor the spread of white daisies and to suppress the growth of black daisies. The growing tide of white daisies diminishes the blanket of black daisies while also reflecting heat away from the planet. These counter-effects settle down or regulate the positive amplification between the sun and the black daisies that had been driving up the temperature.

When the model is set into motion, Daisyworld soon maintains the temperature of its virtual climate at a steady level despite the increasing strength of its sun. It does so automatically, with no goal in mind but only the mutual interplay of negative and positive feedbacks: “No foresight or planning is required by the daisies only their opportunistic local growth when conditions favor them” (Lovelock). The systemic interplay between the black and white daisies models the mutual coupling of two Gaian feedback loops, either of which can exert a negative--that is, regulatory or stabilizing--effect on the other to achieve and conserve a virtual homeostasis. Daisyworld's climate remains stable until the model’s solar forcing becomes too great for the system to control. Driven past that tipping point, Daisyworld life goes extinct.

--adapted from Bruce Clarke, Gaian Systems: Lynn Margulis, Neocybernetics, and the End of the Anthropocene, forthcoming in 2020 from the University of Minnesota Press.

Also see Daisyworld at Wikipedia.