The Earth’s atmosphere contains about 21 per cent oxygen. What would happen if it contained half, or twice, as much? With half as much, animals like us would struggle to move around and stay alive. Twice as much oxygen, on the other hand, would be wonderful to breathe, but terrestrial life would be consumed by fire; in an atmosphere that rich, even damp wood burns well, fires could not be controlled, and the forests would disappear. Our 21 per cent is a good number, not only because we’re used to it, but because it makes for an active – and not too active – biosphere.
Why is the oxygen percentage what it is? Is it because this is the ‘natural’ level for a planet, or for a planet like ours, given Earth’s size and distance from the sun? Not at all: a chemically ‘normal’ atmosphere for a planet like ours would be very different. Our atmosphere is unusual and its composition is the product of life itself. In particular, the oxygen level that keeps us alive is maintained by other living things. How should we think about this? What sort of account should be given of the shaping of the conditions of life by life itself?
In the 1970s James Lovelock, independent scientist and inventor, proposed the Gaia hypothesis. He argued that the Earth regulates itself, and responds to change, in the same sort of way that a single living organism does. The Earth acts to keep itself alive. Lovelock’s new book, written in his mid-nineties, looks back on his life and work, on the Gaia hypothesis, and on the chemical history of the Earth. He also looks forward, as the title suggests, to the next decades and millennia of the Earth’s history. One of Lovelock’s aims is to relate the large-scale history of the Earth, seen through the lens of Gaia, to the environmental problems we are grappling with today, and he does this in a novel way. The most recent stage in Gaia’s evolution, he says, began in 1712, when Thomas Newcomen succeeded in building the first practical steam engine for pumping water. Newcomen’s engine ran on coal, and his invention set in motion an ongoing chemical interaction. Many early steam engines, including Newcomen’s, were used to control flooding in mines, so the mining and burning of coal facilitated further mining and burning of coal, as well as powering the steamships and trains that came with the invention of more efficient engines. This, for Lovelock, wasn’t just an event in human history but an event in the chemical history of the Earth: ‘Our mistake when we started the Anthropocene [the era of substantial human influence on the Earth] was to fail to notice that inadvertently we were the catalyst of the reaction between the carbon of coal and the oxygen of the air.’ Industrialisation, with all its benefits and ills, followed.
We can’t, as Lovelock sees it, wish this chemical event away, or sensibly blame the industrialists who were the means by which the reaction began and by which it continues to happen. When he talks of ‘our mistake’, he doesn’t mean to criticise the people who didn’t see what was happening at the time – they had no way of realising. Instead, Lovelock regards this history, I think, as a rather natural sequence, perhaps even as something bound to happen; the Earth stored vast amounts of carbon as fuel and also created the oxygen-rich atmosphere needed to burn it off. If sufficiently intelligent animals, like Thomas Newcomen, then evolve, the Earth will burn its stored carbon. The consequences include environmental changes that we will have to learn to live with. Lovelock sometimes describes our future as involving an ‘orderly retreat’ into high-density and highly managed human environments reminiscent of Singapore, and beyond that, perhaps a move from the wet carbon-based chemistry we have now to a silicon-based future, after we ‘merge with our electronic creations’.
Lovelock was born in 1919. At first he trained as a chemist, at the University of Manchester, but has since roved through several scientific fields. He briefly held an academic post at Baylor College of Medicine in Texas, and has had other spells in large institutions, but for most of his career he has worked as an independent scientist and consultant. Early on he designed several instruments for analysing chemicals, especially for detecting tiny amounts of substances in larger mixtures, like the atmosphere. In 1957 he invented an extraordinarily sensitive device for this kind of analysis, the electron-capture detector, which makes use of the tendency for some molecules, including many pesticides, to snare a passing electron that has been liberated by radiation in a gas. The number of electrons captured can be precisely tracked, and indicates the presence of different molecules of interest – including some very important pollutants.
In 1961 Lovelock was invited to work in the US with Nasa on exploration projects aimed at the Moon and Mars. These projects led to the work that eventually made Lovelock famous. He took part in discussions of how life might be detected on other planets, especially with instruments sent on spacecraft. Was there, though, a possibility of answering these questions at long range? Could we see from Earth whether there is life on Mars? Yes, Lovelock argued: it can be done by looking at the chemistry of the planet’s atmosphere, about which we can learn a fair amount using Earth-bound telescopes. Planets with life should have atmospheres that look very different from those of planets without it. In the atmosphere of a planet with life, various chemicals will be ‘out of equilibrium’: they will depart from the stable states that ordinary physical processes will tend to bring about. Lovelock thought we could see, even from here, that Mars has an atmosphere different from that of a living planet.
This was the beginning of Lovelock’s thinking about how the activity of living organisms affects the physical and chemical properties of a planet like Earth. Eventually, around 1972, he introduced the Gaia hypothesis (William Golding suggested the name). The American cell biologist Lynn Margulis quickly took up the idea and became a significant early supporter and developer of the theory. Margulis, who died in 2011, was an adventurous scientist whose career, despite some dismaying wrong turns (she argued that HIV isn’t only not the cause of Aids, but doesn’t exist as a biological entity at all), included some truly field-changing work. In the 1960s she argued for a theory of the origin of ‘eukaryotic’ cells – complex cells like the ones that make up our own bodies – according to which they came about when, long ago, one cell swallowed another. The swallowed bacterium became the mitochondria that power our cells today. Some time later, the cells that gave rise to plants swallowed a further passenger of this kind, giving rise to the chloroplasts that make plant photosynthesis possible. This theory had first been proposed in 1910 by the Russian botanist Konstantin Mereschkowski. In 1967 Margulis revived and made a much more detailed case for the view, using a range of microscopic observations of cells. Later genetic evidence showed that Margulis was almost certainly right – not about all the details, but about the crucial events – and the ‘endosymbiotic’ theory of the eukaryotic cell is now a standard part of textbook biology.
The idea of Gaia wasn’t completely new: some aspects of the hypothesis had been anticipated by another Russian scientist, Vladimir Vernadsky. But Lovelock – who knew nothing of the neglected Vernadsky – presented his version with force and detail and it quickly became famous. The starting point, again, was the idea that what we habitually regard as ‘givens’ – the Earth’s atmosphere, the temperature, the kind of light that reaches us on the surface – are products of life. But Lovelock’s hypothesis also goes beyond this to claim that Gaia seeks, through a mechanism of self-regulation of the sort exhibited by organisms, to maintain factors like temperature and oxygen in states that are favourable to itself, the living Earth. The resulting conditions need not be favourable to us – we are just one part of it. The strongest statements of the hypothesis hold that the Earth really is a living organism.
Can this be true, the strongest view on the table, that the Earth is an organism? Biologists, perhaps surprisingly, don’t have a definite, ‘official’ theory of what an organism is – a theory of what features an object must have to be considered an organism. Not only that, but there is also a kind of roughness in many of the analyses that have been given. This might look like a hole in biology, but it’s not. The concept of an organism has, over the last century or so, evolved a mild indefiniteness that reflects real features of the living world.
Some of the best recent work on this topic has been done by David Queller and Joan Strassmann, of Washington University in St Louis, in their studies of insects and of stranger beasts, such as tiny amoebas which join to form crawling colonies. Queller and Strassmann classify systems using two dimensions, co-operation and conflict. Systems are more organism-like, more ‘organismal’, when their parts show a high degree of co-operation and low conflict. Do we need to include both features, co-operation and conflict: isn’t one the flipside of the other? No, Queller and Strassmann say: a system may display a lot of co-operation and a lot of conflict at the same time. Human societies are like this.
What co-operation means here is, roughly speaking, co-operation in maintaining a system’s structure and pattern of activity, using sources of energy and other raw materials to resist the forces of decay. An organism might not take the form of an animal like us. A honeybee colony, for example, is very organismal, despite its physical disconnectedness and freely moving parts. Different pieces of one organism may also have different origins. Some squid, for example, have bacteria living within them that light up the squid’s body, and a squid-bacteria combination can be seen as a single organism. There has been a huge amount of research in recent years on the close relations between humans and the beneficial bacteria in our guts. Perhaps a human organism is both partners, animal plus bacteria, living as a unit. A clearer example would be a cow, which has a stronger dependence on internal bacteria to digest its food.
Is a cow-plus-bacteria, or a bee colony, really an organism, or is this just a colourful metaphor? That is the wrong question. We find many differences of degree, grey areas as well as clear cases, a variety of ways that a system can be partly or somewhat organism-like. Systems can evolve to be more or less organismal over time, as co-operation increases or decreases. Biologists have moved away from strict definitions in this area because sharp boundaries aren’t to be found.
So how organismal is the Earth? If it’s a matter of degree, the Earth scores low. It’s the scene of a great deal of conflict, and many of the parts not in conflict don’t have that much to do with one another. There is a good deal of co-operation, but the co-operative systems form pockets. The bodies of organisms like us are pockets of co-operation between cells, and there are many other pockets – of looser and tighter co-operation. Co-operation, though, is far from the norm, and that is a consequence of basic features of the evolutionary processes that shape the living world. Co-operation is built by means of evolutionary competition, and the scene of that competition is the Earth.
One objection that has been made to Gaia by biologists is that if the Earth were an organism, it would have to be embedded in evolutionary processes in a particular way. It would have to be a member of a population of planets or biospheres, each of which might reproduce, and hence evolve by the transmission of useful traits that happen to appear. Earth is not a member of a population of that kind. On the face of it, Gaia has the wrong relationship to evolutionary processes to qualify as an organism, but once the concept of an organism is loosened up as I outlined earlier, the picture changes somewhat.
If a cow (or squid) plus its helpful internal bacteria makes up an organism, this entity doesn’t reproduce as a unit. Bacteria and cows reproduce separately, and come together to form combinations, year after year. A cow-plus-bacteria is a recurring entity. Let’s take another example, with a lower grade of organismality and some features more evocative of Gaia. Various acacia trees in tropical countries live in tight coalitions with ants. The acacias grow hollows as homes for the ant colonies, and sometimes feed them. The ants, in turn, defend the tree, biting or stinging animals which would like to eat it. The acacia and ants, like the cows and bacteria, don’t reproduce as a unit, but do so separately, and come together to form new ant-acacia combinations. These combinations aren’t paradigm cases of organisms, but they have some degree of organismal character.
Suppose we now scale up, and consider not pairs of species but thousands of species, including also their effects on their physical surroundings. Do we then reach something like Gaia? We don’t. It’s a central part of current biology to consider systems at many different scales, and to consider hidden interactions between what look like unrelated factors, but there can be systems at large spatial scales without these being organisms. An organism is one kind of system, not the only kind, and it arises only in special conditions. In the ant-acacia case, members of two species have evolved a co-operative relationship because there are benefits to both sides. Most interactions between species, and most ecological systems, aren’t like this. Instead, organisms are often bound together by competition and co-evolution. ‘Co-evolution’ might sound harmonious, but much of the time it isn’t; the term denotes no more than a mutual evolutionary influence. Disease-causing organisms and parasites co-evolve with their hosts. In the ant-acacia case, there is a mutual benefit, but this benefit involves – and comes about because of – competition and conflict that are visible once we look further out. The trees evolved their peculiar ant-housing shapes by means of evolutionary competition among trees: trees that housed ants reproduced more than trees that did not. The evolution of these trees was a consequence of pressure imposed by animals interested in feeding on those trees. Such co-operative interactions evolve in a larger competitive context, and the Earth as a whole is the scene – and in some ways the sum – of those largely competitive interactions.
Indeed, there is a kind of inevitability to the competitive character – the non-organismal character – that the overall scene on Earth displays. Once life evolves on a planet, it will come to contain reproducing parts; it will be populated by entities (like bacteria, plants and animals) that make more of themselves. Accidental mutations with different effects will arise in these reproducing entities, and the ones with inherited traits that enable them to reproduce more effectively will become more common at the expense of others. Reproductive ‘competition’ isn’t a perfect description of this, as it suggests a sort of malevolent intention, but it’s the best simple term available. As part of the process, coalitions and alliances will arise – between cells in our bodies, between bees in their colonies, between ants and acacias – but they are forged in competition with other living things. Earth, and anything on a similar scale and produced in a similar way, will always be a different kind of system from an organism. In such a system life will have many effects, including effects on things that we might be tempted to regard as physically ‘given’ – things like gases in the atmosphere and the temperature on the Earth’s surface. But the choice here isn’t between Gaia, on the one hand, and on the other a picture in which the physical properties of Earth are unaffected by its organisms. Instead, the choice is between different views of what those effects are, and why they’re the way they are.
Tangled in talk of Gaia are two big ideas. It’s one thing – and Lovelock deserves considerable credit for getting people to think seriously about this – to say that the Earth forms a single system, in which the living parts affect factors that might otherwise be thought too large and impervious to be sensitive to life. But it’s quite another to say that this system, the Earth, is an organism or is organism-like. And in his defences of Gaia, Lovelock does often write as if the choice is between Gaia and a view in which organisms have very little effect on the planet. When the biologist Ford Doolittle criticised earlier versions of Gaia, Lovelock replied: ‘What he and other evolutionists seem to ignore is the fact that the presence and the products of life inevitably and inexorably modify the environment.’ Whether or not some biologists did ignore this fact at various times, or at least downplayed it, to accept it isn’t the same thing as accepting Gaia.
My argument, then, is that the Earth can form a single interacting system without being at all like an organism. In response, Lovelock might say that we have to explain the stability, and the continuing life-friendliness, of the Earth. There are balances and beneficial exchanges: surely there is a kind of de facto co-operation when plants exhale oxygen for us and we exhale carbon dioxide for them? I would reply that feedback between different living things is indeed ubiquitous, and some kinds of feedback help life to continue. But those benefits to life as a whole are by-products – they’re accidental. The interactions between species are consequences of the traits and behaviours that evolutionary processes within those species give rise to, and those processes are driven by reproductive competition within each species. The upshot of all these evolved behaviours and chemical reactions may be helpful to life as a whole, or not helpful, as the case may be. If a new behaviour, or new chemical product, that was advantageous within some particular species would doom life on Earth if it became common, that fact won’t stop its becoming common. From the fact that life still exists, we can tell that traits too antagonistic to life itself, however beneficial to the organisms that bear them, must not have arisen. If they had, we wouldn’t be around to discuss the matter. But that isn’t what kept those traits at bay.
Lovelock wants to suggest that somehow there’s more to the situation than that. He talks, for example, of goals: ‘Gaia’s goal is to maintain a habitable planet.’ This looks, at first, like a very dramatic claim, as if Lovelock were attributing a kind of agency to the Earth; suddenly, we see ourselves as surrounded by a huge purposive presence. But at least officially, that is not what he means. His concept of ‘goal’ is about as minimal as it could be: elsewhere, he says that any state a system reliably tends to reach, for whatever reason, is a ‘goal’ of the system.
A different concept of ‘goal’, of intermediate strength, can be used to ask and answer an important question about Gaia and the Earth. Let’s say that an activity is directed towards a goal if it has been shaped by some process of design or selection so that it tends to produce that outcome. That sense of goal-directed activity is neither too anthropocentric nor too washed-out to be interesting. Various systems within our bodies have the goal, in this sense, of keeping our temperature within a certain range. Then we can ask whether Gaia’s goal is, in this sense, to maintain a habitable planet, and the answer is no. The Earth has not been shaped by some process of design or selection so that its combined activities tend to keep the planet habitable.
I said earlier that among the wide range of effects that living things have on the physical and chemical nature of the planet, some may involve feedback that helps life itself to continue. The fact that the Earth is not like an organism doesn’t make it impossible for such relationships to exist. If they come about, they do so as fortuitous by-products of the evolution of particular living things. If we find one kind of feedback of this type, that gives us no reason to expect to find others. In contrast, suppose we find a new system somewhere that is an organism – a new kind of animal, or perhaps a stranger case like the ones Queller and Strassmann work on. In that case we would expect to find a whole range of ways that the system acts to keep itself alive. It will be far from perfect, but its history will have been one in which natural selection has continually honed the organism’s ability to make use of resources and deal with problems. When a new problem arises, it may well have resources for responding to it, at least to some extent. No living thing can respond to every new threat, but organisms can often adapt to some of them. When we talk about Gaia as an organism, it suggests that the same sort of picture applies to the Earth. It suggests that when we find one planet-scale effect of life that helps life on Earth to continue, we should expect to find others; we should expect to find a package of ways through which the system acts to maintain itself. It suggests that when a new problem arises, the Earth may well have hidden resources for responding to it such that it can continue to pursue its goals. But given how evolution shapes living things on Earth, none of that is true.
Lovelock’s freewheeling Rough Ride to the Future brims with an intellectual inventiveness that complements the hardware inventions he has produced over the years. The book also, in many places, takes on the quality of a rant. Lovelock rails at modern academia with its committees, safety rules and political correctness: ‘today’s equivalent of the theocratic oppression of Galileo’. Even the peer review of scientific papers, which one would think is far better for a lone scientist than an informal old-boy network would be, is described as ‘similar … to the Inquisition’. There is some casual political commentary: he distrusts ‘equal opportunity’ (it ‘smells of demagoguery’) and gives an approving nod, in the Victorian style, to ‘bloodstock and breeding’. Lovelock is also careless with facts. An important example, pointed out by George Monbiot, is his endorsement of erroneous claims made by anti-environmentalists that a ‘ban’ on DDT following the publication of Rachael Carson’s book Silent Spring in 1962 led to a huge rise in deaths from malaria. In fact the US ban on DDT in 1972 allowed its use for disease control along with manufacture for export, and the international agreement that covers DDT (the Stockholm Convention) explicitly allows the use of DDT for control of disease-causing insects. There are other misleading remarks too: Lovelock says a couple of times, for example, that the symbiotic swallowing of one cell by another led to the evolution of muscles in animals – ‘the first muscle cells were endosymbionts.’ But what that symbiotic process actually led to – more than five hundred million years before the first muscle – were cells with mitochondria that are seen not only in animals but also in plants, fungi and much single-celled life. Such mistakes make the cascade of factual claims in the book – claims that Lovelock uses to disparage ‘green’ policies, such as moves towards renewable sources of energy – feel rather shaky.
Since Lovelock introduced the Gaia theory, about forty years ago, our picture of the history of the Earth has become more eventful, less a story of stability and more one of change. Many scientists believe now that our planet went through one or more stages described as ‘Snowball Earth’, in which all the Earth’s seas were largely frozen over. The last such episode may have ended a little before the period of great evolutionary invention, the Cambrian. Our picture of the history of oxygen has also changed. Rather than remaining within a tight and stable range, it now seems likely that its levels have seesawed. In the Carboniferous, about three hundred million years ago, oxygen levels seem to have risen to somewhere between 27 per cent and 35 per cent. This probably aided in the evolution of the disconcertingly huge insects – dragonflies with seventy-centimetre wingspans – that existed at the time and may have also aided the evolution of animal flight. Oxygen levels then plummeted during the Triassic (the early period of the dinosaurs), reaching a gasping 15 per cent. Through all these changes oxygen is clearly part of a system, a system with a history and featuring many kinds of feedback. Oxygen produced early in life’s history tended to form compounds in the earth’s crust with elements like iron; eventually it accumulated as the Carboniferous plants turned the Earth into a giant ‘oxygen bar’; those plants were smothered and gave rise to fossil fuels, which we burn – or decide not to burn – today. There’s a rich set of interactions here, and a role for life in the continual remaking of the Earth, but it is not co-operative, not organism-like, and not driven by goals. Or, more accurately, the goals that will have some role in bringing about the next stage in the Earth’s chemical history are not the grand-scale goals of the Earth itself, but the goals of reflective human agents who have the capacity to work out how they want things to go.