Editing Gaia hypothesis (section)

====Daisyworld simulations====
{{Main|Daisyworld}}
[[File:StandardDaisyWorldRun2color.gif|thumb|280px|Plots from a standard black and white [[Daisyworld]] simulation]]

In response to the criticism that the Gaia hypothesis seemingly required unrealistic [[group selection]] and [[Cooperation (evolution)|cooperation]] between organisms, James Lovelock and [[Andrew Watson (scientist)|Andrew Watson]] developed a mathematical model, [[Daisyworld]], in which [[Competition (biology)|ecological competition]] underpinned planetary temperature regulation.<ref name="daisyworld">{{cite journal
|date = 1983
|title = Biological homeostasis of the global environment: the parable of Daisyworld
|journal = Tellus
|volume = 35B
|pages = 286–9
|bibcode = 1983TellB..35..284W
|doi = 10.1111/j.1600-0889.1983.tb00031.x
|last1 = Watson | first1= A.J. | last2= Lovelock | first2= J.E
|issue = 4
}}</ref>

Daisyworld examines the [[Earth's energy budget|energy budget]] of a [[planet]] populated by two different types of plants, black [[Asteraceae|daisies]] and white daisies, which are assumed to occupy a significant portion of the surface. The colour of the daisies influences the [[albedo]] of the planet such that black daisies absorb more light and warm the planet, while white daisies reflect more light and cool the planet.  The black daisies are assumed to grow and reproduce best at a lower temperature, while the white daisies are assumed to thrive best at a higher temperature.  As the temperature rises closer to the value the white daisies like, the white daisies outreproduce the black daisies, leading to a larger percentage of white surface, and more sunlight is reflected, reducing the heat input and eventually cooling the planet. Conversely, as the temperature falls, the black daisies outreproduce the white daisies, absorbing more sunlight and warming the planet. The temperature will thus converge to the value at which the reproductive rates of the plants are equal.

Lovelock and Watson showed that, over a limited range of conditions, this [[negative feedback]] due to competition can stabilize the planet's temperature at a value which supports life, if the energy output of the Sun changes, while a planet without life would show wide temperature changes.  The percentage of white and black daisies will continually change to keep the temperature at the value at which the plants' reproductive rates are equal, allowing both life forms to thrive.

It has been suggested that the results were predictable because Lovelock and Watson selected examples that produced the responses they desired.<ref>{{cite journal | doi = 10.1023/A:1023494111532 | date = 2003 | last1 = Kirchner | first1 = James W. | journal = Climatic Change | volume = 58 |issue=1–2| pages = 21–45 |title=The Gaia Hypothesis: Conjectures and Refutations | s2cid = 1153044 }}</ref>