Biological homeostasis of the global environment: the parable of Daisyworld

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Abstract
The biota have effected profound changes on the environment of the surface of the earth. At the same time, that environment has imposed constraints on the biota, so that life and the environment may be considered as 2 parts of a coupled system. Unfortunately, the system is too complex and too little known for us to model it adequately. To investigate the properties which this close-coupling might confer on the system, a model was developed of an imaginary planet having a very simple biosphere. It consisted of just 2 spp. of daisy of different colors and was first described by Lovelock (1982). The growth rate of the daisies depends on only 1 environmental variable, temperature, which the daisies in turn modify because they absorb different amounts of radiation. Regardless of the details of the interaction, the effect of the daisies is to stabilize the temperature. The result arises because of the peaked shape of the growth-temperature curve and is independent of the mechanics by which the biota are assumed to modify the temperature. The elements of a biological feeback system which might help regulate the temperature of the earth are sketched out.