Abstract
 

Some notions of Gaia would have us believe that life on Earth is a component of a planetary system that is in some sense self-regulating or homeostatic. Moreover, that this homeostasis benefits life in the sense that those conditions that are good for life are in part stabilised by the effects of life. Much debate about Gaia has centered around the parable of Daisyworld. This simple mathematical model demonstrated that planetary homeostasis can arise with a set of arguably plausible physical assumptions. There have been numerous extensions and developments of the original Daisyworld. Some of this work has been motivated by relaxing the set of assumptions required for homeostasis to emerge.

Until relatively recently, one fundamental assumption seemed necessary:
that somehow stabilising negative feedback loops rather than destabilising positive feedback loops had to be somehow selected for. In many Daisyworld models this selection was performed by those that designed the model with the assumption that  organisms experienced an increase in fitness when altering the environment in ways that were beneficial to life. This led to James Kirchner arguing that proponents of homeostatic Gaia were advocating a form of 'lucky Gaia'. If the Earth is homeostatic Gaia-like then the planet has simply been lucky to produce negative feedback loops. In conjunction with Andy Watson's anthropomorphic arguments, we have a possible explanation for the emergence and persistence of Gaia in the universe.

In my talk I will show why James Kirchner was wrong. Gaia can emerge in the presence of initially equally probable negative and positive feedback loops. In that respect, the Earth need not have been particularly lucky (although it has certainly been fortunate in many other ways). The explanatory mechanism is something called rein control and is potentially very general and widespread on the Earth and perhaps any other planet that harbours life. In showing how negative feedback loops can emerge in Daisyworld, a more nuanced notion of planetary homeostasis is developed that is arguably a form of homeorhesis and more closely correlates with the actual history of the Earth.