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Gaia: is there scientific evidence for this intriguing, inspiring, infuriating hypothesis?


Just on 30 years ago I came across an intriguing book, the then relatively unknown Gaia: A new look at life on Earth (OUP 1979) by an ‘independent scientist’, J.E. Lovelock. My earliest impression of it may seem surprising to many people now. I was infuriated. I was infuriated not by Lovelock’s hypothesis per se, but by what I impugned was his underlying purpose behind proposing this model.

Gaia was presented by Lovelock as a fifteen year quest to substantiate the model:

“in which the Earth’s living matter, air, oceans, and land surfaces form a complex which can be seen as a single organism and which has the capacity to keep our planet a fit place for life.”

That was an intriguing hypothesis. The infuriating part I found was the implication that thanks to Gaia our fears of pollution-extermination may be unfounded. In particular I found the logic of chapter 7 (Gaia and Man: the problem of pollution) to be pernicious. On the untested assumption that Gaia did exist, and in the form suggested by Lovelock, he proposed the idea “there is indeed ample evidence that pollution is as natural to Gaia as is breathing to ourselves and most other animals.” The philosopher in me took umbrage at his glib jibes at the various current environmental perspectives – chiding them for their naive perspectives.


It took at least another careful read of Gaia before I appreciated Lovelock’s perspective, which his follow-on books left the reader in no doubt. Gaia: a new look at life on Earth was followed by The Ages of Gaia in 1988 (both books were revised for 2nd editions in 1995), Lovelock’s autobiography Homage to Gaia: the life of an independent scientist (OUP, 2000) was followed by the more strident The Revenge of Gaia (Allen Lane, 2006) and The Vanishing Face of Gaia: a final warning (Allen Lane, 2009). There was still the unanswered question – does Gaia exist?

The reaction to the question of Gaia’s existence is one of the the great legacies of Lovelock’s book. Lovelock’s eloquence and novelty of hypothesis inspired many responses and continues to provoke fierce debate. It has taken some time for a concise critical scientific analysis, in a form accessible to the interested educated reader, of the major assertions and arguments underpinning the Gaia hypothesis to be written. Toby Tyrrell, Professor of Earth Systems Science at the University of Southampton has managed to deliver this.

In On Gaia: a critical investigation of the relationship between life and Earth (Princeton University press, 2013), Tyrell asks and answers the question: “Does the Gaia hypothesis hold up in court?”


Tyrrell gets down to business in a succinct manner. He distills the Gaia hypothesis to three main facts, or classes of facts that Lovelock has advanced in support of the hypothesis. They are:

  1. The environment is very well suited to the organisms that inhabit it
  2. The Earth’s atmosphere is a biological construct whose composition is far from expectations of (abiotic) chemical equilibrium, and
  3. The earth has been a stable environment over time, despite external forcings.

Tyrell reminds us that the Gaia hypothesis is not the only one that looks at the relationship between life and environment on Earth. So in his book he takes these three facts and examines the evidence for them in the light of two other competing hypotheses; the Geological and the Coevolutionary.

The Geological hypothesis was the dominant paradigm among geologists and other scientists at the time Gaia was written. According to this way of thinking life has been a passenger on Earth, helplessly buffeted around by a mixture of geological forces and astronomical processes. Life adapts to this environment but does not itself affect it.

The Coevolutionary hypothesis assumes that there is two way traffic: not only does the nature of the environment shape the nature of life, life also acts as a force that shapes the planetary environment. There is one obvious, although too easily missed, difference between the coevolution of life and climate and of two life forms; such as the interactions between predators and prey and between hosts and parasites for example. There is no equivalent cumulative evolutionary process that builds better-adapted oceans or atmospheres over time. This means that this hypothesis makes no claims about the wider outcomes of the interaction. The Gaia hypothesis suggest that the outcome of the interaction has stabilized the planet and kept it favorable for life; Coevolution is neutral about such claims.

Having carefully framed the questions, and presented some viable alternatives, Tyrell then very eloquently and elegantly (in that scientific sense) looks at the evidence for which hopythesis fits the facts best.

In doing this he takes us on quite an adventure. We look at extremophiles and life over the glacial and interglacial eons, because as Lovelock states “the most important property of Gaia is the tendency to optimize conditions for all terrestrial life”. In other chapters by examining, over time, deep sea plankton nitrogen and phosphorus ratios, and atmospheric oxygen and methane levels Tyrrell convincingly demonstrates that the earth’s atmosphere is a biological construct. Having established that life has the power to shape the Earth he then examines what are the environmental alterations are produced.

By carefully examining two evolutionary innovations that have most obviously shaken the world: (i) the evolution of oxygen-yielding photosynthesis, and (ii) the colonization of land by the first forests, we find that life has always changed to exploit and closely fit it, as it must because of evolution. Finally by examining the rocks, glaciation levels, seawater chemistry and the ups and downs of greenhouse gases for the past 500 million years Tyrell concludes that Gaia has not helped to keep the Earths environment stable – because the research shows that the environment has not been stable.

The final chapter is a masterful example of clear thinking. Tyrrell revisits the road travelled, weaves the strands together and draws his conclusion that Gaia is a fascinating but flawed hypothesis. Tyrrell does not stop there he proposes new “intriguing research topics” that have arisen as a consequence of evaluating the Gaia hypothesis. As well he reminds us why this evaluation is important: planetary management requires solid understanding, Gaia imbues undue optimism, and the need for an unbiased worldview.

On Gaia: a critical investigation of the relationship between life and Earth (Princeton University Press, 2013), is a great contribution to an important scientific, and human debate. Toby Tyrrell demonstrates both a fine grasp of science, and science communication.  An intelligent reader will find this book rewarding, for both these reasons.

On Gaia: A Critical Investigation of the Relationship between Life and Earth
Toby Tyrrell

Cloth | 2013 | US$35.00 / £24.95 | ISBN: 9780691121581, 320 pp. | 6 x 9 | 16 halftones. 31 line illus. 12 tables.