From Bill Hamilton, University of Oxford
I am grateful for the publicity that New Scientist has given to my
paper with Tim Lenton on biogenic cumulus clouds
(“Send in the clouds”, 30 May, p 28).
But Lynn Hunt’s article puts an unjustified slant on our ideas in relation to Gaia.
The natural selection mechanism we suggest could, it is true, be a component
of a thermostat, but no one has yet shown how the thermostat could be adjusted
appropriately. Indeed, it is not even clear if this thermostat is wired the
right way: it could “click” on and stay on until the world freezes for all that
our study shows. It may be that a thermostat is there but the evolutionary (or
other) process leading to it needs to be explained.
In the paper we emphasised the current lack of principles to explain the
evolution of life-like properties in a single system that does not replicate
itself. We cite the critiques of Gaia on these lines by Ken Caldeira and by
Richard Dawkins, and also mention the general ineffectiveness of Neo-Darwinian
processes for global adaptation. Today complexity theory is often invoked as a
route to adaptation that is not based upon natural selection. It has, however,
yet to show how any adaptation can arise at all.
For those who find the evidence for homeostasis of the planet compelling,
this leaves several options. The gloomiest of these is the anthropic principle:
here the homeostasis is counterfeit—we happen to have survived this far
but there is no guarantee that life on the planet will not destroy itself. A
second is panspermia, the idea that space is full of spores, that stable
planetary systems have contributed more of them than have unstable ones, and
that newly colonised planets are thus receiving ever more stabilising mixes of
colonists. This brings in natural selection and thus hope, but it is
theoretically dubious and is unsupported by data. Thirdly, there is the
possibility that there is a selection process inherent in community assembly
which has yet to be described.
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For the time being, however, it seems best to assume that the planet is
subject to a set of out-of-control thermostats, and that human rationality, via
science, is its main hope for homeostasis.
