Daisyworld



Daisyworld is a thought experiment describing an ultra-simplified Gaian system: a planet whose only life consists only of daisies with varying colors. It was invented by James Lovelock to answer scientific critiques claiming that for Gaia to establish planetary homeostasis, she must have a guiding intelligence capable of planning for the future and deliberately changing environmental variables. Daisyworld demonstrates that in fact, homeostasis can easily be established without any conscious intent.

The model works because the different species of daisy survive best at different temperatures. Because their dark color allows them to absorb lots of heat from the sun, black daisies do best when the planet is cool. But as they spread across the planet's surface, they lower its albedo so it absorbs more heat. This makes the climate more hospitable for lighter-colored daisies, which would otherwise get too cold as they reflect away so much of the light that lands on them. The spread of white daisies then increases the planet's albedo again, cooling the climate and eventually leading to a balance.

This negative feedback loop allows the daisies to naturally vary their relative abundance in response to changing solar energy input, keeping the planet near an optimum temperature. For example, if the sun gets cooler, the planet's temperature will drop, but this will provide a competitive advantage for darker-colored daisies. As they grow more numerous, the planet's albedo will decrease and it will absorb more heat, pushing it back toward an optimum temperature.

The system has limits. For example, if the sun gets too hot, eventually even a planet covered with only white daisies can't reflect enough heat to keep the planet in the habitable temperature range, and the daisies die out.