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Gaia theory




The Gaia hypothesis/theory comes in various flavors. It tells that the Earth’s biota, waters, atmosphere and rocks comprise a system that “behaves like” an organism. The characteristics of an organism being referred to are metabolism, homeostasis, homeorhesis and autopoiesis. Even if the Earth’s biosphere is just a simple causal cycle like James Watt’s steam enginge governor, early cyberneticists have associated this with the Aristotelian causal category of finality or teleology (Mario Bunge, Causality 4th. ed., p.155,32), thus inevitably provoking much criticism of the idea of Gaia by late modern natural philosophers and ensuing adaptations by her proponents.

Gaia was first proposed by chemist James Lovelock and refined together with microbiologist Lynn Margulis? in the early 1970s.

In Lovelock’s terminology Gaia hypothesis refers to this first version and Gaia theory to the further elaborated version of the 1980s. Today the term Gaia hypothesis is used mainly by Gaia skeptics. From the glossary of Lovelock 2009:

Gaia Hypothesis. James Lovelock and Lynn Margulis postulated in the early 1970s that life on Earth actively keeps the surface conditions always favorable for whatever is the contemporary ensemble of organisms. When introduced, this hypothesis was contrary to the conventional wisdom that life adapted to planetary conditions as it and they evolved in their separate ways. We now know that the hypothesis as originally stated was wrong because it is not life alone but the whole Earth system that does the regulating. The hypothesis evolved into what is now Gaia theory.

Gaia Theory. A view of Earth introduced in the 1980s that sees it as a self-regulating system made up from the totality of organisms, the surface rocks, the ocean and the atmosphere tightly coupled as an evolving system. The theory sees this system as having a goal – the regulation of surface conditions so as always to be as favorable for contemporary life as possible. It is based on observations and theoretical models; it is fruitful and has made ten successful predictions.

Strong Gaia, weak Gaia, Earth system science, etc.

Problem and Paradigm

Popper 1962:

These theories appeared to be able to explain practically everything that happened within the fields to which they referred. The study of any of them seemed to have the effect of an intellectual conversion or revelation, opening your eyes to a new truth hidden from those not yet initiated. Once your eyes were thus opened you saw confirming instances everywhere: the world was full of verifications of the theory.

On the positive side Tim Lenton, a major Gaia theorist described it as a hypothesis generator [LeW03]:

Both “lucky Gaia” and “probable Gaia” suggest a strong research agenda: to find and understand these feedbacks

In Kant‘s analysis of views of the organismic world a certain degree of teleologic thinking is posited as unavoidable. In his Critique of the Power of Judgment (K1790, §75) he famously states:

[I]n terms of merely mechanical principles of nature we cannot even adequately become familiar with, much less explain, organized beings and how they are internally possible. So certain is this that we may boldly state that it is absurd for human beings even to attempt it, or to hope that perhaps some day another Newton might arise who would explain to us, in terms of natural laws unordered by any intention, how even a mere blade of grass is produced.

Predictions, tests and results relevant to the Gaia theory

Lovelock ([L03], [L09], etc.) has a list of Gaia theoretic insights and results:

Mars is lifeless (1968)Atmospheric compositional evidence shows lack of disequilibriumStrong confirmation, Viking mission 1975
That elements are transferred from ocean to land by biogenic gases (1971)Search for oceanic sources of dimethyl sulphide and methyl iodideFound 1973
Climate regulation through biologically enhanced rock weathering (1973)Analysis of ice-core data linking temperature and CO2 abundanceConfirmed 2008, by Zeebe and Caldeira

CO2 regulation is a major sticking point. Do Zeebe and Caldeira prove that biologically enhanced rock weathering is essential? Perhaps chemical rock weathering suffices.

Zeebe and Caldeira [ZC08]:

we show that the mean long-term trend of atmospheric CO2 levels is no more than 22 p.p.m.v. over the past 610,000 years. When these data are used in combination with indicators of ocean carbonate mineral saturation to force carbon cycle models, the maximum imbalance between the supply and uptake of CO2 is 1–2% during the late Pleistocene. This long-term balance holds despite glacial–interglacial variations on shorter timescales. Our results provide support for a weathering feedback driven by atmospheric CO2 concentrations that maintains the observed fine mass balance.

Origin: Life on Mars?

From Lovelock and Giffin 1969:

Confusion often attends attempts to apply the thermodynamic concepts of entropy and equilibrium to living systems and this present topic is no exception. It is generally agreed that it is a property of life to reduce its internal entropy through the assimilation of free energy and the excretion of degraded energy to the environment. Controversy can arise, however, over the size of the maximum unit of life. There is, for example, no doubt that an animal has a highly ordered chemical composition, but its environment to which disorder is rejected includes the atmosphere; it might seem pointless therefore to seek evidence of life by looking for order in the chemical composition of the atmosphere. If instead of individual living organisms, however, the planetary ecosystem itself is regarded as the maximum unit of life, the problem resolves. In an ecosystem, the atmosphere can have an ordered role as the conveyor belt for products between, for example, the plant and animal kingdoms of the Earth, or their analogues elsewhere. With this large unit, the atmosphere is an internal component of the living system, and the environment is now space, to which disorder is rejected in the form of degraded solar energy.


If the atmosphere of the Earth is a biological contrivance, then it is reasonable to consider that the components are maintained at an optimum or near optimum composition for the ecosystem. For example, the Earth’s climate is strongly dependent upon the atmospheric pressure, that is, the total amount of oxygen and nitrogen, and on the concentration of infrared absorbency gases such as carbon dioxide and water vapour. The concentration of these components are directly or indirectly under biological control. It may not therefore be an unreasonable speculation to consider the possibility that the Earth’s climate is also maintained at or near an optimum for the ecosystem.

It is interesting to ask, why is the oxygen concentration maintained at 21%. It is a fact that the energy required for the ignition of organic compounds changes by about 70% for each 1% change in oxygen concentration at the atmospheric level. Life at even 25% oxygen might be very uncomfortable, especially for trees. The removal of oxygen by grass and forest fires may set the upper limit of 21% but it seems more likely that oxygen is actively controlled at a safe maximum.

Inspiration: Schrödinger’s “What is Life?”

Erwin Schrödinger’s little book (1944) is said to be one of the most influential books of 20th century science. It is based on lectures delivered in Dublin 1943 to a general audience.

The book has inspired many physicists to move into biology and kicked off the race to unravel the structure of DNA. It lays out two research programs: How come order from order and how come order from disorder. The latter was an inspiration to James Lovelock, as one can guess from the quote above. He writes (2000)

Most of Schrödinger’s book is an optimistic prediction of how life is knowable. The eminent molecular biologist, Max Perutz, has recently commented that little in Schrödinger’s book is original, and what is original is often wrong. This may be true; but I, like many of my colleagues still acknowledge a debt to Schrödinger for having set us thinking in a productive way.

Freeman Dyson (1999) sums up the contents:

In Schrödinger’s book we find four chapters describing in lucid detail the phenomenon of biological replication and a single chapter describing less lucidly the phenomenon of metabolism. Schrödinger finds a conceptual basis in physics both for exact replication and for metabolism. Replication is explained by the quantum mechanical stability of molecular structures, whereas metabolism is explained by the ability of a living cell to extract negative entropy from its surroundings in accordance with the laws of thermodynamics. Delbrück penetrated more deeply than his contemporaries into the mechanics of replication because he was not distracted by the problem of metabolism. Schrödinger saw the world of biology through Delbrück’s eyes. It is not surprising that Schrödinger’s view of what constitutes a living organism resembles a bacteriophage more than it resembles a bacterium or a human being.

Emphasis added. Schrödinger explains that he uses the improper term negative entropy instead of free energy to make himself more understandable to his nonspecialist audience.

Schrödinger’s paradox and a thermodynamic foundation of Gaia theory

The book’s second research program, order from disorder is also termed the Schrödinger paradox. In biology it has only slowly gained momentum, accelerating only in recent decades with the emerging field of thermodynamic ecology and the systems approach to evolution. (See e.g. Meysman and Bruers (2007), R.J.P. Williams and Frausto da Silva (2002) or the popular book Into the Cool by E.D. Schneider and D. Sagan (2005).) Regarding the still speculative principle of maximum entropy production A. Kleidon (2009) writes:

nonequilibrium thermodynamics and MEP show great promise in allowing us to formulate a quantifiable, holistic perspective of the Earth system at a fundamental level. This perspective would allow us to understand how the Earth system organizes itself in its functioning, how it reacts to change, and how it has evolved through time.


The term Gaia was suggested to Lovelock, who was seeking “a convenient four-letter word” for his hypothesis, by his fellow villager and walking companion William Golding (Nobel prize in literature 1983).

Gaia is an etymologic root in terms like geometry, geology, pangea, etc.

Gaia is a Greek primordial goddess, Grandmother Earth. Instead of examining the convoluted family tree of the Greek pantheon it is perhaps more illuminating to look at their oracles which were influential institutions of public and private life: The most important was the Delphic oracle. In prehistoric times it was like many other oracles owned by Gaia. According to myth, the olympian god Apollon, grandson of Gaia, conquered the Delphi oracle by slaying its female guardian serpent Pytho. To add insult he left her rot on the ground. Apollon represents civilization.

Critque, first round

Many neo-Darwinian evolutionary biologists responded with vehement criticism to the early Gaia hypothesis, most prominently Doolittle (1981) and Dawkins (1982). Lovelock (2009) recalls:

The trouble started … when Doolittle wrote his lively and well-written critique of Gaia. Interestingly, he chose to publish it in the American New Age magazine Coevolution Quarterly, edited by Steward Brand. Scientists may pretend to deplore New Age, but that does not stop them from reading its publications, and in no time Gaia’s face was turned to the wall. … Neither Lynn Margulis nor I could make a convincing defense – partly because, as we stated it, the Gaia hypothesis was wrong. We had said that organisms, or the biosphere, regulated the Earth’s climate and composition. … in his book The Extended Phenotype, Richard Dawkins showed that this was impossible.

Dawkins’ book also exhibits some of the basic misunderstandings of Gaia theory:

Lovelock rightly regards homeostatic self-regulation as one of the characteristic activities of living organisms, and this leads him to the daring hypothesis that the whole Earth is equivalent to a single living organism

His explanations of the nature of the atmosphere are representative of his ideas. The Earth has much more oxygen than is typicai of comparable planets. It has long been widely suggested that green plants are probably almost entirely responsible for this high oxygen content. Most people would regard oxygen production as a byproduct of plant activity, and a fortunate one for those of us who need to breathe oxygen (presumably, too, we have been selected to breathe oxygen partly because there is so much of it about). Lovelock goes further, and regards oxygen production by plants as an adaptation on the part of the Earth/organism or “Gaia” (named after the Greek Earth goddess): plants produce oxygen because it benefits life as a whole. He uses the same kind of argument for other gases that occur in small amounts:

What, then, is the purpose of methane and” how does it relate to oxygen? One obvious function is to maintain the integrity of the anaerobic zones of its origin [p. 73].

Another puzzling atmospheric gas is nitrous oxide … We may be sure that the efficient biosphere is unlikely to squander the energy required in making this odd gas unless it has some useful function. Two possible uses come to mind… [p. 74].

Another nitrogenous gas made in large volumes in the soil and the sea and released to the air is ammonia … As with methane, the biosphere uses a great deal of energy in producing ammonia, which is now entirely of biological origin. Its function is almost certainly to control the acidity of the environment… [p. 77].

The fatal flaw in Lovelock’s hypothesis would have instantly occurred to him if he had wondered about the level of natural selection process which would be required in order to produce the Earth’s supposed adaptations. Homeostatic adaptations in individual bodies evolve because individuals with improved homeostatic apparatus pass on their genes more effectively than individuals with inferior homeostatic apparatuses. For the analogy to apply strictly, there would have to have been a set of rival Gaias, presumably on different planets. Biospheres which did not develop efficient homeostatic regulation of their planetary atmospheres tended to go extinct. The Universe would have to be full of dead planets whose homeostatic regulation systems had failed, with, dotted around, a handful of successful, well-regulated planets of which Earth is one. Even this improbable scenario is not sufficient to lead to the evolution of planetary adaptations of the kind Lovelock proposes. In addition we would have to postulate some kind of reproduction, whereby successful planets spawned copies of their life forms on new planets.

I am not, of course, suggesting that Lovelock believes it happened like that. He would surely consider the idea of interplanetary selection as ludicrous as I do. Obviously he simply did not see his hypothesis as entailing the hidden assumptions that I think it entails. He might dispute that it does entail those assumptions, and maintain that Gaia could evolve her global adaptations by the ordinary processes of Darwinian selection acting within the one planet. I very much doubt that a model of such a selection process could be made to work: it would have all the notorious difficulties of “group selection”. For instance, if plants are supposed to make oxygen for the good of the biosphere, imagine a mutant plant which saved itself the costs of oxygen manufacture. Obviously it would outreproduce its more public-spirited colleagues, and genes for publiospiritedness would soon disappear. It is no use protesting that oxygen manufacture need not have costs: if it did not have costs, the most parsimonious explanation of oxygen production in plants would be the one the scientific world accepts anyway, that oxygen is a byproduct of something the plants do for their own selfish good. I do not deny that somebody may, one day, produce a workable model of the evolution of Gaia (possibly along the lines of “Model 2” below), although I personally doubt it. But if Lovelock has such a model in mind he does not mention it. Indeed, he gives no indication that there is a difficult problem here.

Other critiques maintain that self-regulation requires a goal set from outside. But teleology is a scientific taboo. As Lovelock quipped,

I know of professors of biology who have trouble with the concept of self-regulation, but they have no difficulty walking!

Rescue: Daisyworld(s)

Daisyworld is a toy model made by inventor James Lovelock. He thought about patenting it as a regulation method. Good toy models are made of few but crucial principles and avoid ad hoc assumptions. E.g. Daisyworld uses realistic radiation physics (checked by planetary spectral measurement), yet disregards space of any dimension.

Original Daisyworld ([WL83], [LL01]) is a cloudless zero-dimensional grey planet illuminated by a varying sun. It is subject to the Stefan-Boltzmann law (as on Earth soil and vegetation approximate black-body radiation) and inhabited by fractions of dark and light daisies with a realistic temperature-growth function (5°C-40°C with optimum at 22.5°C). Their population dynamics follows the simple equation of Carter and Prince (1981) modelling aspects of plant biogeography.

The basic math of classic Daisyworld can be laid out on one page ([Wi06], [WADWL08]). Maddock (1991) suggests that Daisyworld is not very sensitive to the type of population model used. The most important point is the temperature-growth function: Daisyworld has apparently only been “disproved” by allowing for growth not limited by temperature.

It is hotly debated if homeostasis is built in or is a fulguration (in the sense of Konrad Lorenz, i.e. emergent). Certainly the assumption of an adapted and homogen(e)ous ecosystem of Daisy species (optimum plant growth at same temperature) runs counter to an interpretation of the model as demonstrating stability against environmental change.

Critique, second round

Daisy World has regulation or altruism built in

Snowball Earth

Reception beyond science

Martin Heidegger ca. 1937:

Nature, extracted out of the realm of being by nature-science - what is happening to her via technology? The growing, or better: simply unwinding destruction of “Nature”. What was she once? The place of the moment of arrival and residence of the gods; when she was resting, still φύσιζ (physis), in the becoming of be-ing itself. Since then she readily became something being, and then even the opposite to “grace”, and after this deposition completely exposed into the enforcement of calculating machination and economy. And finally only “landscape” remained and recreational opportunity and now this even calculated into the gigantic and prepared for the masses. And then? Is this the end? Why is Earth keeping silent at this destruction? Because neither contention with a world nor the truth of Being is bestowed on her. Why not? Is it because the giganto thing Man gets the bigger the more it shrinks?

(Transl. by M.G. from Beiträge zur Philosophie (vom Ereignis), Nr. 155. Posthum. (1936-1938) in: Gesamtausgabe Bd. 65. – An english translation with reduced Germish gibberish is by R.Rojcewicz and D.Valliga-Neu, 2012)


ToDo: Tidy up references according to How to: references and add clickable labels as suggested in the forum (but that seems to not really work - see [ZC08] - and typesetting square brackets seems to overwhelm the markup parser…)

  • _[Wi06] David M. Wilkinson, Fundamental Processes in Ecology: An Earth Systems Approach, Oxford University Press, Oxford, 2006.
  • test… without this entry the following (exhibiting a parser bug) gets swallowed:

  • (1)ZC08\] R.E. Zeebe, K. Caldeira, Close mass balance of long-term carbon fluxes from ice-core CO2 and ocean chemistry records, [Nature Geoscience]( **1** (2008), 312 - 315

category: earth science