Book review – On Gaia: A Critical Investigation of the Relationship between Life and Earth

10-minute read
keywords: earth sciences, ecology

The scientist, environmentalist, and futurist James Lovelock is probably best remembered for the Gaia hypothesis: the notion that the Earth is a giant self-regulating system that maintains conditions suitable for life on the planet. It has gained a certain respectability in academic circles over the decades, but how justified is this? In my previous reviews of Lovelock’s original 1979 book Gaia: A New Look at Life on Earth and the 1995 follow-up The Ages of Gaia, I was critical of various assumptions and claims expressed therein. At the same time, I am aware that other, more knowledgeable people have worked on this idea for years, so what do I know? In On Gaia, Earth system scientist Toby Tyrrell gives a thorough and dispassionate overview of the scientific evidence and whether it supports Gaia. This, then, is the third of a four-part review series that explores the Gaia hypothesis in greater detail (see also part 1, part 2, and part 4).

On Gaia: A Critical Investigation of the Relationship between Life and Earth, written by Toby Tyrrell, published by Princeton University Press in July 2013 (hardback, 311 pages)

Given the holistic, top-down nature of the Gaia hypothesis, any critique of it will have to cover a lot of ground and straddle many disciplines. Tyrrell tackles this challenge in several ways. The book is well structured with good use of numbered sections to keep information organised while relegating digressions and technical details to a fascinating collection of sometimes long endnotes. Furthermore, the book is self-contained and you do not strictly need to read Lovelock’s work. I did so as I felt it is incumbent on me to be well-informed, plus I wanted to be able to judge for myself how fair Tyrrell’s critique is. Lastly, by going back to first principles, On Gaia is a terrific primer on palaeoclimatology and Earth system science.

Additional challenges in evaluating Gaia are that Lovelock both modified the idea with time and was not very clear in his definitions. Rather, it appears as “a collection of several related hypotheses, often couched in rather vague terms” (p. 4). Even so, the different formulations have three assertions in common: 1) the environment is hospitable to life (i.e. its biosphere), 2) life can change the environment, and 3) the environment has been constant through time. Evaluating these claims is at the heart of this book and takes up five of the ten chapters. Tyrrell furthermore compares Gaia to two alternative explanations dubbed the geological and coevolutionary hypotheses. The former says that Earth’s environment is primarily shaped by geological forces (this was the default paradigm when Lovelock formulated his hypothesis). The latter only says that life and the planet influence each other but remains neutral on whether the outcome will be favourable for life or not. It is credited here to Stephen Schneider and Randi Londer who, in their 1984 book, borrowed the term coevolution from population biology and applied it to the interaction between climate and biosphere, and this idea is alive and well.

Before delving into the meat of the book, Tyrrell discusses the question of mechanism. How could something like Gaia evolve? Part of this is a history lesson as Lovelock unwittingly chose a bad moment to introduce Gaia. Just as evolutionary biologists were embroiled in fierce arguments against group selection, in steps Lovelock with an idea even more radical than natural selection acting on the level of groups of organisms: how about the whole planet? Tyrrell outlines why it was, and still is, considered unlikely by evolutionary biologists: it would require cooperation amongst very distantly related organisms which is simply not what we observe in the real world. There are admittedly limited circumstances where natural selection leads to regulation of local environments and Lovelock made a lot out of them. However, both Gaia-as-physiological-homeostasis and Gaia-as-superorganism work as crude analogies but, Tyrrell explains in some detail, “any suggestion of a deeper resemblance is very misleading” (p. 30). Similarly, though Lovelock’s Daisyworld model showed that planetary regulation could theoretically emerge from individual actions, it is not a realistic description of how the climate and biosphere interact. This material, covered in chapter two, flagged up many points of criticism I had not even considered. Shame on me, but also, how terribly interesting.

“Evaluating Gaia is complicated because Lovelock modified the idea with time and was vague in his definitions. Even so, three assertions crop up repeatedly and the core of the book compares them with the data.”

The core of the book compares the three abovementioned assertions with the data. Lovelock’s first assertion is that the environment is well-suited to life. As I suspected, he gets the arrow of causation backwards: adaptation to one’s environment via natural selection is a sufficient explanation, even if it can give “the impression that all environments have been made to be uncannily well suited to their inhabitants” (p. 202). Moreover, this is not even always true. Lovelock has suggested that Gaia likes to keep the planet cool. Tyrrell fleshes this out in two further chapters by looking at the biological effects of temperature. Biological processes proceed faster at higher temperatures and do so not in a linear but in an exponential fashion. Though there are exceptions (this is biology after all), the overall tendency is for physiological rates, biomass, and biodiversity to increase with higher temperatures. Furthermore, after considering a range of factors, Tyrrell makes the point that ice ages are unfavourable: the planet is simply too cold for life to thrive.

The evidence for Lovelock’s third assertion, that the environment has been held constant by Gaia, also crumbles under the weight of the evidence against it. This is a chapter that showcases the marvellous array of proxies that palaeoclimatologists have developed. By cross-referencing multiple such indirect lines of evidence (e.g. ice cores, lake sediments, microfossils, tree rings, and many others) they have reconstructed an increasingly detailed picture of Earth’s past climate. Tyrrell here considers evidence from stratigraphy, ocean chemistry and acidity, temperature, greenhouse gases, and erratic climatic episodes such as Snowball Earth and more recent ice ages to convincingly show that our planet’s climate has been anything but constant.

Only Lovelock’s second assertion, that life can influence the planetary environment, is supported by the data. Tyrrell makes no bones of it either: “The evidence […] is sparkingly clear” (p. 127). He explores in more detail two factors that are under biological control: the composition of Earth’s atmosphere and the nitrogen-to-phosphorus ratio in seawater. Indeed, the fact that Earth’s atmosphere is far from chemical equilibrium and contains short-lived gases such as oxygen and methane was one of Lovelock’s original observations that sent him down this path.

” Tyrrell pulls no punches in his conclusion […] Many of Lovelock’s claims are not supported once carefully evaluated and there is nothing that can be explained exclusively by the Gaia hypothesis.”

The above is but a brief summary of some of the key arguments that Tyrrell makes. There are various other interesting points I have not touched on here and the whole book, including its extensive endnotes, deserves close reading. Tyrrell pulls no punches in his conclusion: “in my view Gaia is a fascinating but a flawed hypothesis [and] a dead end” (pp. 208–209). Many of Lovelock’s claims are not supported once carefully evaluated and there is nothing that can be explained exclusively by the Gaia hypothesis. Circling back to the other two hypotheses, the geological one also has its flaws. Instead, the data support the coevolutionary hypothesis: life and the planet influence each other, though not always to life’s benefit.

On a side note, maybe we just got lucky. Though I am not a fan of such explanations because they are by definition beyond the purview of scientific enquiry, chapter 9 brings in the weak anthropic principle: the fact that we are here as observers asking these questions means that life by definition must have survived up to this point in time. In other words, we might just have gotten lucky. How lucky? Unfortunately, our sample size of known habitable worlds in the universe is one, so we lack the data to quantify the odds. This chapter to me was the weakest in the book and it felt like Tyrrell was stepping outside of his comfort zone to dabble in philosophy*. The most satisfying thing Tyrrell has to say about this is that it likely was a combination: “crude regulatory mechanisms on Earth increased the chances of continued survival from vanishingly small to just very small, but […] luck also played a part” (p. 191).

Tyrrell’s book-length argumentation and evaluation to arrive at his conclusion is, in my opinion, calm, reasoned, fair, and still relevant despite the book now being ten years old. He focuses on the facts and I would even say that he gives Lovelock a pass in some places, pointing out how many palaeoclimatological findings were made after Lovelock first published his ideas. Though true, what irks me is not that Lovelock was initially mistaken, we all are at times, but that he never recanted nor acknowledged the growing body of evidence against his idea. Instead, he doubled down on his assertions, as evidenced by the prefaces to the 2000 reissues of both Gaia and The Ages of Gaia, while the 2016 preface to Gaia does not mention Tyrrell’s book.

“Tyrrell’s book-length argumentation and evaluation to arrive at his conclusion is, in my opinion, calm, reasoned, fair, and still relevant despite the book now being ten years old.”

You might wonder if it matters whether the Gaia hypothesis is right or wrong (Lovelock certainly did not think so). In closing the book, Tyrrell argues that, in the face of anthropogenic climate change, having a true picture of how the Earth system functions has never been more important. The risk of the Gaia hypothesis is that it fosters complacency: “confidence in Earth’s natural resilience is emotionally comforting, but is most likely to be misplaced and could be dangerously deceiving” (p. 214). Importantly, “there is no Gaian safety net to come to the rescue if we mismanage it” (p. 218). That is a sentiment I can very much find myself in.

In conclusion, On Gaia has confirmed my suspicions while pointing out many other flaws I had not even considered yet. Even so, Tyrrell praises Lovelock for his originality and breadth of vision, recognizing that “his audacious concept has helped to stimulate many new ideas about the Earth, and to champion a holistic approach to studying it” (p. 209). I found this a phenomenally interesting book and highly recommend it. Though he builds on previous edited collections such as Scientists on Gaia and Scientists Debate Gaia, Tyrrell has done readers a tremendous service in writing such a focused and in-depth review of the Gaia hypothesis and presenting it in such an accessible manner.

But wait, the preface to The Ages of Gaia also mentioned how environmentalist Jonathon Porritt in 1994 expressed his opinion that the idea of Gaia is too important to be the sole domain of “finicky scientists” (p. xvi therein). For the last instalment of this four-part review series, I will take a step back from the hard science and turn to Michael Ruse’s The Gaia Hypothesis for a wider appreciation of Lovelock’s ideas.

* After publication of this review, the author kindly linked me to subsequent papers by himself and others that further explore the role of chance in the long habitability of our planet.

On Gaia