Lovelock and Watson developed the Daisyworld computer simulation model to prove that purposeful action by the biosphere is not required for temperature regulation, but instead that processes of natural selection are sufficient to accomplish the task. Although the earth is too complex a system to be modelled mathematically, Daisyworld is a simplified model in which much of the complexity has been stripped away and only the fundamental relationships and characteristics are retained. The hypothetical Daisyworld orbits a sun whose radiant energy is slowly increasing. Daisyworld is seeded with two varieties of daisy as its only life forms: black daisies and white daisies. White petalled daisies reflect light, while black petalled daisies absorb light. At the beginning of the simulation, the sun's rays are weak and Daisyworld is too cold to support any life. Its surface is barren and grey. As the luminosity of the sun's rays increases, germination of black daisies becomes possible. Because black daisies absorb more of the sun's radiant energy, they are able to increase their individual temperatures to healthy levels on the still cool surface of Daisyworld. As a result they thrive and the population soon grows large enough to increase the average temperature of Daisyworld. As the surface heats up it becomes more habitable for white daisies whose competing population grows to rival the black daisy population. As the two populations reach equilibrium, so does the surface temperature of Daisyworld, which settles on a value most comfortable for both populations. The second phase of the simulation documents what happens when the sun's luminosity continues to increase, heating the surface of Daisyworld beyond a comfortable range for the daisies. This temperature increase causes the white daisies, who are better able to stay cool because of their high albedo, or ability to reflect sunlight, to gain a selective advantage over the black daisies. White daisies begin replacing black daisies, which has a cooling effect on Daisyworld. The result is that Daisyworld's surface temperature remains habitable, in fact almost constant, even as the luminosity of the sun continues to increase. In the third phase of the simulation, the sun's rays have grown so powerful that soon even the white daisies cannot survive. At a certain luminosity the population crashes, and the barren, grey surface of Daisyworld, no longer able to reflect the sun's rays, rapidly heats up. At this point in the simulation solar luminosity is programmed to decline, retracing its original path to the initial value. Even as it declines to levels that previously supported vast populations of daisies in the third phase, no daisies are able to grow because the surface of barren, grey Daisyworld is still far too hot. Eventually the power of sun's rays decrease to a more comfortable level, allowing white daisies to grow, and the planet begins cooling.
Later extensions of the simulation include rabbits, foxes and other species. One of the findings of these simulations is that a larger number of species improves the temperature regulation.
copyright©Wilna Panagos