Gaia theory – Reflections on life on earth

William Grey, University of Queensland

John Gribbin and Mary Gribbin James Lovelock: In Search of Gaia, Princeton, Princeton University Press, 2009 (272 pp). ISBN 9-78069113-750-6 (hard cover) RRP $39.95.

John Kricher The Balance of Nature: Ecology’s Enduring Myth, Princeton, Princeton University Press, 2009 (252 pp). ISBN 9-78069113-898-5 (hard cover) RRP $35.95.

Peter Ward The Medea Hypothesis: Is Life on Earth Ultimately Self-Destructive? Princeton, Princeton University Press, 2009 (208 pp). ISBN 9-78069113-075-0 (hard cover) RRP $38.95.

We inhabit an extraordinary planet. Our nearest celestial companions—the Moon, and our sister planets Venus and Mars—provide striking abiotic (lifeless) contrasts to the conditions on planet Earth. Just how the Earth got this way, and how it has managed to stay this way, is a fascinating story, some elements of which we are beginning to understand. Working out the detail is a project that will no doubt continue for a long time.

The robust scientific consensus is that about 3.5 billion years ago organic chemistry transformed our then lifeless world by somehow generating self-replicating molecules. These precursors of life, by steps unknown, eventually produced the most remarkable molecule (that we know of) in the universe: deoxyribonucleic acid (DNA). Over unimaginable billion year epochs of geological time, DNA molecules have managed to construct, through Darwinian selective mechanisms, complex protein structures—which include us, as well as the rest of the living world which surrounds us. Always opportunistic, life has become ever more complex and wonderfully adapted to the world in which it exists.

Three new books published by Princeton University Press address the story of life on Earth. The books are, however, very different in their conclusions and in their quality. James Lovelock’s Gaia theory is the theme which connects each of their concerns.

John and Mary Gribbin’s James Lovelock: In Search of Gaia is a history of Lovelock’s theory which is woven into a biography of his life as a scientist and inventor. It is engaging, well researched, well written and accessible to non-specialists. Combining Lovelock’s biography with an account of Gaia theory is appropriate: Gaia theory is the most outstanding achievement of Lovelock’s remarkable life. Anyone who is interested in life on Earth, or in the achievements of a remarkable man who has done much to deepen our understanding of life, should read the Gribbins’ homage to Lovelock. It is a delight.

For conventional science, life is a process existing within, and adapting to, an abiotic world.

The authors are well qualified to undertake this biographical and expository task. John Gribbin, a visiting fellow in astronomy at the University of Sussex, has written many popular science books including In Search of Schrödinger’s Cat. Mary Gribbin has written many books with John, including Richard Feynman: A Life in Science.

In the conventional scientific story, outlined above, life is conceived as a process which exists within, and adapts to, an abiotic world. Lovelock’s big idea was the audacious conjecture that life does not merely adjust itself to the conditions within which it exists, but acts systematically and collectively on a planetary scale to shape conditions such as atmospheric composition and temperature in a way which redounds to its own advantage. This is the central claim of Gaia theory—a designation which the Gribbins prefer to the Gaia ‘hypothesis’. Hypotheses progress to theories when their conjectures are vindicated by successful predictions. Some of these successes are discussed by the Gribbins, including the role of living systems in pumping carbon dioxide out of the atmosphere and locking it up, which is achieved by several mechanisms including, importantly, the deposition of carbonate shells by marine organisms and by soil microorganisms which chemically accelerate the rate of rock weathering to form limestone—the silicate-carbonate geochemical cycle.

Perhaps the greatest problem which now confronts humanity is caused by anthropogenic carbon emissions which, combined with land clearing and other unsustainable agricultural practices, are overwhelming the capacity of these vital carbon pumps. These activities are likely to initiate a cascade of consequences that, if not addressed, will create grave problems for humanity. Lovelock is pessimistic about our capacity to sustain human populations at anything like their present levels without seriously disrupting the processes on which our individual and collective well-being ultimately depends.

According to Gaia theory, living systems act collectively in a way so as to maintain conditions favourable for their continuation. This is achieved by the operation of life-based negative feedback mechanisms which maintain a range of basic parameters—such as the Earth’s average surface temperature, atmospheric composition, ocean acidity and salinity—within ranges which favour the flourishing of life. This suggests, at bottom, that Gaia has operated over the aeons to maintain a state of vital balance.

This conception of balance is the target of John Kricher’s The Balance of Nature: Ecology’s Enduring Myth. Kricher, a Professor of Biology at Wheaton College, is impressed by the fact that over geological time Gaia has had many faces; indeed so many faces that it makes no sense to talk of stability at all.

According to Gaia theory, living systems act collectively to maintain favourable conditions.

Take a snapshot of Gaia’s face 3.5 billion years ago and then (say) every 100 million years until now—that is 35 snapshots—and you would clearly see that the face is not the same. There is no identity; nothing constant; only perpetual change. The same lesson is apparent over shorter time scales. Suppose we were to take snapshots at geological eye-blink intervals of 100 thousand years—that would deliver 35 thousand snapshots—and again we would be more impressed by discontinuity and change than by any feature that persisted or endured. This snapshot analogy is not used by Kricher, but I think it fairly represents his underlying argument.

The idea of balance in nature, according to Kricher, is an enduring myth based ultimately on Aristotelian misconceptions about teleology, or purpose, in nature—which he identifies as the basis of an unscientific paradigm. His argument at this point is murky. Kricher’s distinction between scientific (that is, respectable) paradigms and unscientific paradigms (or belief systems) is never satisfactorily explicated. His idea of a paradigm is at best distantly related to the canonical account provided in Thomas Kuhn’s The Structure of Scientific Revolutions. No paradigm, for Kuhn, is straightforwardly falsifiable.

Kricher’s epistemology, then, is confused—and so too, at times, is his history. There is disappointing muddle, for example, in his confusion of Einstein’s views about quantum theory and his views about cosmology. However within his own field of scholarly expertise, ecology, Kricher provides some useful historical background—especially in chapter 6, where he outlines the pioneering ecological theories of (among others) Frederic Clements (1874–1945), Henry Gleason (1882–1975), Arthur Tansley (1871–1955) and Charles S. Elton (1900–91).

Kricher’s rejection of balance in nature leads him to a position of personal discomfort. He is a biologist who intuitively—and in my view admirably—supports conservation values such as the defence of biodiversity. But if there is no natural balance, and Gaia’s face is ever-changing, why should we be concerned to support the present accidental and ephemeral constituents of the biosphere? If any idea of balance is naïve, as Kricher maintains, then surely we should be unconcerned about such things as climate change and its effects on global ecosystems. Kricher confesses that his conclusion at this point ‘does not make me rest easy’ (p. 154).

In my view Kricher is right to feel troubled by the destination to which his argument has taken him. He struggles in the final chapters to support wholly admirable environmental values, but it is unclear how these can be reconciled with his central argument. We are supposed to act to ‘sustain’ the planet. But if there is no preferred state—no balanced system—to sustain, then why should we—indeed how can we—bother? Kricher’s argument seems to me to be guilty of a fallacy of scale—because there is no evident stability or balance on very long geological scales, he appears to conclude that we should reject the idea of stability or balance altogether. But that would be as fallacious as supposing that because, from a long term view, the history of an organism is a succession of episodes of illness and injury, there can be no coherent notion of that organism’s balanced, preferred (that is, healthy) state.

If life is inherently programmed to eliminate itself then it isn’t doing a very good job.

Yet even from the geological perspective of deep time it is perverse to suppose that there is complete absence of continuity. Certainly the biosphere has moved through a dramatic sequence of transformations in its 3.5 billion year history. But the facts that prokaryotic life has persisted over this time scale, and that DNA has adapted and recoded a succession of disparate protein structures to survive in the changing conditions of the planet, surely points to prodigious stability. Without doubt there have been a succession of spectacular insults to life on Earth—atmospheric change, vulcanism, asteroid impacts, and a relentless increase in solar flux to name just a few. What is astonishing is not so much the changing face of Gaia as the fact that Gaia has (so far) always managed to recover from such intense and varied global cataclysm.

Kricher sees living systems in a perpetual state of disturbance. Lovelock sees living systems in a continuing sequence of corrections by which they are able to persist. These are different aspects of a single dynamic process. Kricher is not wrong to point out that the face of Gaia, in the long run, has changed radically. But he is insufficiently impressed by Gaia’s resilience, her capacity to survive massive extraterrestrial and volcanic global devastation, as a result of which she stumbles, but then manages nevertheless to pick herself up and continue on. That seems to be missing something very striking and important.

Gaia is the goddess in Greek mythology who helped to bring order out of chaos. Medea is a very different character in Greek mythology—the tempestuous and destructive wife of the ancient hero Jason, best known from the famous depiction by Euripides. Peter Ward, professor of biology and Earth and space sciences at the University of Washington and an astrobiologist with NASA, believes that Medea provides a better metaphor than Gaia for understanding the history of life on Earth.

The Medea hypothesis is fundamentally opposed to Gaia theory. Living systems, Ward suggests, do not act in a way that promotes their own long-term survival. Living systems rather are inherently self-destructive. Living systems do not shape an abiotic planet into a decent place for DNA to flourish (as the Gaia theory proposes); DNA instead is responsible for a succession of global catastrophes, though the reliable processes of inorganic chemistry have managed, fortuitously, to save the day and rescue life from total annihilation. It is however a puzzle, if life is as self-destructive as Ward’s Medea hypothesis claims it to be why, after more than three billion years, it has not yet managed to wipe itself out completely. If life is inherently programmed to eliminate itself then it isn’t doing a very good job.

Ward includes a discussion of the silicate-carbonate cycle, the process by which carbon moves from living systems to rocks, which places insufficient emphasis on the important role played by micro-organisms in weathering. Indeed his very confused and repetitive description silicate weathering (in chapter 3) provides little confidence in his grasp of the basic chemistry. Irritatingly, he repeatedly appeals in this chapter (and also elsewhere in the text) to papers which cannot be found in his bibliography—which is however puzzlingly replete with references mentioned nowhere in the text.

Ward is an enthusiastic revisionary about the history of global temperature, which he thinks provides a compelling objection to Gaia theory. Over the last 3.5 billion years, he suggests, the history of temperature has been very different to the conventionally accepted story. Indeed he is so enthusiastic about the history of global temperature that the same graph is gratuitously repeated three times (pp. 80, 107, 111). This graph is based on the ratio of oxygen isotopes in specific formations in the geological record (pristine chert rocks) which are strikingly at odds with temperature estimates from other sources.

The very distant future is a fascinating issue for philosophical reflection but is of no concern now.

The graph is certainly striking. It shows, for example, that during the Archaean period (about three billion years ago) the average surface temperature of the planet was above 100°C. (That must have given Gaia something to think about! It is difficult to imagine how life as we know it could survive without liquid water.) The graph also shows that during periods of global glaciation 2.3 billion and 700 million years ago (the so-called ‘snowball’ Earth periods) the average surface temperature was 50–60°C. This is just absurd! It is physically impossible for such a high average surface temperature to exist at a time of global glaciation. Moreover temperature claims in the text (see, for example, p. 106) are quite inconsistent with the graph provided.

Ward’s arguments against Gaia theory generally consist of pointing out dramatic events which significantly disrupted, or overwhelmed, Gaian control mechanisms. These include microbial planetary engineering, which changed an atmosphere of nitrogen and carbon dioxide to a methane smog, and then several billion years ago to an atmosphere with free oxygen, and the major extinction events, each of which transformed the face of Gaia. Ward characterises these as Medean events because of their destructive impact on the then extant assemblage of life forms. The critical measure of life’s success for Ward is not biodiversity or complexity, but biomass. I have serious misgivings about using biomass as a criterion for life’s success. Biodiversity and complexity in food chains and trophic networks contribute importantly to ecosystem stability—though of course Ward’s skepticism about ecosystem stability (shared with, and to some extent derived from, Kricher) naturally leads him to downplay these factors. However, I cannot explore these worries in detail here.

Lovelock, through the lens of Gaia theory, interprets what Ward sees as Medean events as exemplars of the way that life forms opportunistically adapt themselves and their circumstances to changed planetary conditions. An atmosphere rich in the greenhouse gases carbon dioxide and methane would have suited Gaia well several billion years ago, when the solar energy output was 30 per cent less than it is today. Today’s anthropogenic geo-engineering with carbon emissions exceeding the biosphere’s carbon sink capacity however, is foolhardy beyond the usual limits of human incaution.

Ward sees our overloading of carbon sinks as another Medean event, showing again that Gaia theory is fundamentally mistaken. Lovelock would look not at the disturbance, but at the consequential adjustment of Gaia to hotter equilibrium state, which may happen with catastrophic consequences—such as a 70-metre sea level rise—for the well-being of our species, and catastrophic also for many of our nonhuman companions.

The Medean hypothesis perversely fails to see that Gaia theory is not about disturbances which change the face of the planet. It is rather about the capacity of the planet to respond to disturbances through processes, mediated by living systems, to achieve new provisional, dynamic, stable states. Gaia’s current interglacial state has suited us well. Industrial civilisation and human agriculture depend upon it. It would be foolish in the extreme to act in a way that might seriously disturb this provisional equilibrium.

Ward includes a discussion of environmentalism and environmental philosophy which I blush to mention. This discussion (chapter 10) reveals little research and less understanding. He confesses that philosophy is outside his comfort zone—the chapter in fact reveals that philosophy is not merely outside his zone of comfort, it is well outside his zone of comprehension.

Gaia theory is not about disturbances which change the face of the planet.

Ward concludes with a profoundly irritating chapter which raises concerns about our planetary future 100 million years hence, and he agonises about policies which may be needed to ensure that the planet survives over this geological time-scale. This discussion manifests the fallacy of scale which tainted Kricher’s thinking. We are now confronted with profound global problems which require our urgent attention if we are to ensure that human civilisation successfully negotiates the next few decades or centuries. This must be the focus of our moral, political and economic agendas. Planet Earth will almost certainly still exist 100 million years hence, in some state or other, but it will not be our planet in any relevant sense. This very distant future is a fascinating issue for philosophical reflection but it is of no concern to us now. The distant future is a distraction from the serious policy issues which humanity urgently needs to address.

The Medea Hypothesis is a disappointing book. Indeed it is a mystery that the publishing house which produced the other two books oversaw the publication of such an assortment of typographical and other careless errors and misunderstandings. The book also includes lamentable referencing and a bibliography which is not only confusingly sorted by chapters, but which also bears little relationship to the so-called arguments which it parades. It is painful to read, and reviewing it has forced me to contravene W.H. Auden’s wise advice to reviewers to write only about good books. The purpose of reviews, Auden argued, is to announce publications which merit the attention of readers; reviewing lamentable failures is a waste of time for both reviewers and readers, because bad books will be forgotten soon enough anyway. There is little doubt that The Medea Hypothesis will soon be forgotten.

Awareness of the threat which global warming poses to humanity is growing, and in December 2009 world leaders met in Copenhagen to address this issue. The outcome of this meeting however was disappointing, and there is no sign yet of either the political will or the policy measures urgently needed to adjust our industrial economies to operate within limits that will sustain the present face of Gaia and allow us, and our descendants, to continue to flourish. This is the major challenge that, individually and collectively, we need to address. Indeed it is perhaps the greatest challenge that humanity has ever faced.


Kuhn, T.S. 1962, The Structure of Scientific Revolutions, University of Chicago Press, Chicago.

Gribbin, J. 1984, In Search of Schrödinger’s Cat, Wildwood House, London.

Gribbin, J. & Gribbin, M. 1997, Richard Feynman: A Life in Science, Viking, London.

William Grey is Associate Professor of Philosophy at the University of Queensland. His research interests include environmental philosophy and metaphysics.