Progress of a Daisyworld-Simulation with many breeds and a medium scale iteration level

Daisyworld simulation is an analogy which shows that life which is adapted to certain kind of environmental conditions by its mere existence slightly (or more) regulates its own environment toward living conditions which are suitable for life. Life has to do so because otherwise the species in borderline conditions could not live at all but would die away if they could not affect their own living conditions toward better. The point here is that if this effect spreads to the environment, like in the Daisyworld example, or if the effect comes via affecting the environment, then life really regulates the living conditions - also in our own planet Earth too - toward what is beneficial to life.

Simulation timeline

At the beginning of the simulation, Daisyworld is so cold that only a few black daisies, and almost no white daises, can survive. Whenever the planet's temperature decreases, the black flowers tend to predominate, they absorb a little heat from the sun, which causes the planet's temperature to rise, allowing a greater proliferation of black daisies, more absorption of heat, and so on. As the planet becomes hotter white daisies begin to breed as well, and eventually the planet reaches a point of temperature equilibrium. Any increase in temperature is combated by a greater proportion of white daisies; any decrease leads to more black daisies. Such a system is remarkably stable against varying solar input; the entire planet maintains homeostasis. Eventually the external temperature becomes too high for the daisies to oppose, and heat overwhelms the planet.

When the simulation is run without the daisies, the planet's temperature proceeds in sync with that of the sun. With the daisies, at the beginning of the simulation there is enhanced warming, and at the end of the simulation enhanced cooling, resulting in a close to equilibrium temperature for most of the simulation. In this way the daisies are modifying the climate to make conditions more hospitable for themselves. However, the Daisyworld system exhibits hysteresis: for some solar constants, the planet has two distinct stable states, typically no life and one almost 100% occupied with life.

Later extensions of the Daisyworld simulation included rabbits, foxes and other species. One of the more surprising findings of these simulations is that the larger the number of species, the greater the improving effects on the entire planet (i.e., the temperature regulation was improved). These findings lent support to the idea that biodiversity is valuable, and sparked the modern biodiversity debate.

Daisyworld has attracted a substantial amount of criticism. It bears scant resemblance to Earth; the system requires an ad-hoc death rate (?) to sustain homeostasis; and the paper blurs the distinction between species-level phenomena and individual level phenomena. However, Daisyworld arguably demonstrates that biologically mediated homeostasis does not require a teleological explanation.

References and implementations

A version of the Daisyworld simulation, with several shades of gray daisies, was included in the Maxis video game SimEarth. Orson Scott Card's novel Xenocide also makes several references to Daisyworld.

See also

• Gaia theory (science)
• Gaia philosophy

External references and links

• (The original paper by Watson and Lovelock introducing the Daisyworld model.)
• Modeling the Gaia Hypothesis: DaisyWorld A test applet of a basic Daisyworld model using a 2D cellular automata.
• A web-based implementation of the Daisyworld model
• Java Applet for daisyworld on a 2D space
• Spatial Daisyworld Model Java Applet and explanation of Daisyworld with evolution
• Modeling Daisyworld including the equations used for it
• A Unix/X11 simulation of Daisyworld.
• Daisyworld Flash Animation Student friendly flash animation illustrating the Daisyworld Computer model found at ThinkQuest.org
• Card, O.S., Xenocide (science fiction novel, sequel to Ender's Game and Speaker for the Dead, Tor, Aug 1991)

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