Testing Gaia Theory with Artificial Life

Abstract

The Gaia hypothesis postulates that the Earth is a self-regulating system, that tends to maintain conditions habitable for life. The hypothesis grew from the recognition that organisms have fundamentally altered their planetary environment - its thermodynamic state, the composition of the atmosphere, the climate, ocean chemistry and the land surface. Changes in the environment have in turn altered organisms’ growth and the forces of natural selection acting upon them and this implies inevitable feedback connections between life and its environment. The resulting world seems remarkably well suited to carbon-based life, and has some important stabilising properties. For example, the Earth’s climate has remained habitable despite a 25% increase in the luminosity of the sun since the origin of life. Known feedback mechanisms more often show a tendency to regulate the environment than to destabilise it. Thus there is arguably an overall tendency for the Earth system to counteract gradual forcing and rapid perturbations that tend to drive the environment away from a habitable state. However, it is not obvious why this should necessarily be the case. If the Earth did not have some regulatory properties, we would probably not be here to remark on them, because life would have perished before evolution produced conscious observers. Furthermore, Gaia poses a puzzle when viewed from a Darwinian perspective: Why should the organisms that leave the most descendants be the ones that contribute to regulating their planetary environment?