It seems somewhat eccentric if not a little absurd to suggest that a planet is a living thing. Earth has life on it, but it’s not a biological organism. Any theory or argument which concludes that the Earth is alive could be safely filed under “wronger than wrong”.
So when James Lovelock and Lynn Margulis first proposed the Gaia Hypothesis in their 1974 paper Atmospheric homeostasis by and for the biosphere: the Gaia hypothesis, some seized on the possible implication that the Earth is a form of biological organism. The Earth is alive? Nonsense!
Why such strong reactions? Because homeostasis - the ability to respond to shocks and changes in such a way as to reduce their impact - is a hallmark of living systems. For example, your body reacts to temperature with shivering if too cold, to produce heat in your muscles, and by sweating and flushing blood to the surface of your skin to cool if too hot.
While Lovelock has developed the theory in numerous scientific papers and books since the 1970s into its contemporary form, his constant claim is that life through its interactions with the environment is a component of a homeostatic system - namely, the planet itself.
Why should we think that the Earth is homeostatic? In the first instance once life started around 3.5 billion years ago it never stopped. Everything alive today can trace its ancestry right back to the origins of life. So despite large changes in the brightness of the Sun, massive impacts and extreme volcanic activity, temperatures on the surface of the Earth have remained within relatively narrow bounds and life has survived. Perhaps we were just lucky. We could also invoke the anthropic principle, reasoning that if life on Earth hadn’t survived then we wouldn’t be here to ask such questions.
Or, perhaps some of the effects of life on Earth have stabilised the planet and made it better able to support life. Why would the Earth do this? There doesn’t seem to be a mechanism by which planets with life can be made more homeostatic, stable, or conducive for supporting life. So in a recently published paper, my PhD student Iain Weaver and I proposed such a mechanism for Gaian homeostasis, whereby complex ecosystems and potentially entire biospheres could be self-stabilising.
How does it work?
We found that a very simple mechanism known as “rein control” can emerge from the complex interactions of life in an ecosystem. Rein control was formulated by Manfred Clynes during the 1960s cybernetics movement as a mechanism to explain physiological control and homeostasis in biological organisms (he also coined the term “cyborg”).
It’s called rein control because it’s like steering a horse with reins - they can only pull, not push, and only in one direction. So to move something left and right you need two reins. If you want to move something in two axes (up/down, left/right) then you need four reins, and so on.
Ecosystems can be very complex with a very large number of species. But rather than this complexity representing a de-stabilising force, instead the many diverse species form many “reins”, with which to stabilise environmental conditions. We found that even after severe shocks, a complex system could return to one of a number of stable states.
Feedback and consequences
As well as shedding light on how Gaian homeostasis may work, our research has other messages for arguably more pressing issues. In order for homeostasis to emerge in any system, there must be a feedback loop. The organisms affecting the environment must “feel” the consequences of these effects, and there must be a flow of information that enables this. It’s an open question to what extent there is this information flow on Earth. Certainly there have been very destabilising events in the past, such as the “great oxidation” of the atmosphere caused by the evolution of photosynthesis. In fact some of the mass extinction events in the past have been largely driven by life.
Climate change seems to be a good contemporary example. The species Homo sapiens is currently changing the composition of the Earth’s atmosphere. The impacts on the environment, through increased average temperatures, loss of Arctic sea ice and ocean acidification, will affect other species, but not have so much of an effect on Homo sapiens - yet. But if we carry on business as usual the predictions are not good, and we will feel the consequences of our actions with destabilised food production as a result of extreme weather events and flooding. By then much larger changes would be required to reduce these impacts.
The countries largely responsible for current and historical carbon dioxide emissions are the most industrialised and typically the richest countries, and so best placed to insulate themselves from the worst consequences of their actions. The irony is that those countries which contributed least to the problem will be those likely to suffer most.
The Earth is arguably the most complex system in the known universe. So while we are a planet-altering species it seems misguided, even dangerous, to think we could control it. Pretty much whatever we do, life - with or without Homo sapiens - will carry on much as it did for the previous 3.5 billion years. It is only by understanding its past evolution and underlying mechanisms that we can hope to continue to be a part of its future.