A hypothesis, first proposed by James Lovelock in 1972, which considers the Earth as an intimately linked system of physical, chemical, and biological processes, interacting in a self-regulating way to maintain the conditions necessary for life. This contrasts with the view that the Earth is merely an inanimate habitat, fortuitously having surface conditions that have supported the evolution of plants and animals. Although named after the Greek Earth goddess, it has a scientific rather than a mystical basis.
The Gaia hypothesis is an ecological theory that proposes that the living matter of planet Earth functions like a single organism. An early recognition of some of the core assumptions of the Gaia hypothesis was given in the book Lives of a Cell by Lewis Thomas. The Gaia Hypothesis has since been supported by a number of scientific experiments and provided a number of useful predictions so is properly referred to as the Gaia Theory.
Since 1971, the noted microbiologist Lynn Margulis has been Lovelock's most important collaborator in developing Gaian concepts (Turney 2003). Encouraged by Margulis, the theory was first publicly mentioned in the article by Lovelock, "Gaia as seen through the atmosphere" in the Journal, Atmospheric Environment 6 (1972) pp.579-580.
Until 1975 it was almost totally ignored.
Today the Gaia theory is more commonly referred to as earth system science, and is a class of scientific models of the geo-biosphere in which life as a whole fosters and maintains suitable conditions for itself by helping to create an environment on Earth suitable for its continuity.
Gaia "theories" have non-technical predecessors in the ideas of many cultures. Today, "Gaia theory" is sometimes used among scientists on the basis that the earlier Gaia hypothesis has withstood rigorous scientific testing. At the second Chapman Conference of the American Geophysical Union, at Valencia in Spain, for instance, Lynn Margulis in her closing address "Modes of Confirmation of the Gaia Hypothesis" conceded that despite being elevated to "Gaia theory" in the 1980s, there was still confusion about what Gaia was in reality. Among some scientists, "Gaia" still carries connotations of lack of scientific rigor and quasi-mystical thinking about the planet Earth. Lovelock's own reframing of the hypothesis as "Geophysiology" and the growing acceptance of "Earth system science" has silenced many of these critics.
Lovelock's initial hypothesis
Lovelock defined Gaia as:
His initial hypothesis was that the biomass modifies the conditions on the planet to make conditions on the planet more hospitable – the Gaia Hypothesis properly defined this "hospitality" as a full homeostasis.
Lovelock suggested that life on Earth provides a cybernetic, homeostatic feedback system operated automatically and unconsciously by the biota, leading to broad stabilization of global temperature and chemical composition.
With his initial hypothesis, Lovelock claimed the existence of a global control system of surface temperature, atmosphere composition and ocean salinity.
Since life started on Earth, the energy provided by the Sun has increased by 25% to 30%;
Ocean salinity has been constant at about 3.4% for a very long time.
The only significant natural source of atmospheric carbon dioxide (CO2) is volcanic activity, while the only significant removal is through the precipitation of carbonate rocks.
Lovelock sees this as one of the complex processes that maintain conditions suitable for life. For Lovelock and other Gaia scientists like Stephan Harding, coccolithophorides are one stage in a regulatory feedback loop.
Controversial concepts
Lovelock, especially in his older texts, has often indulged in language that has later caused fiery debates. For instance many attacked his statement in the first paragraph of his first Gaia book (1979), that "the quest for Gaia is an attempt to find the largest living creature on Earth." Is Gaia really an organism? And in what sense does the cybernetic system called Gaia seek "an optimal physical and chemical environment for life on this planet"?
Lynn Margulis, the coauthor of Gaia hypotheses, is more careful to avoid controversial figures of speech than is Lovelock. In 1979 she wrote, in particular, that only homeorhetic and not homeostatic balances are involved: that is, the composition of Earth's atmosphere, hydrosphere, and lithosphere are regulated around "set points" as in homeostasis, but those set points change with time. Accordingly, the Earth is not a living organism which can live or die all at once, but rather a kind of community of trust which can exist at many discrete levels of integration.
Critical analysis
Basis
This theory is based on the simple idea that the biomass self-regulates the conditions on the planet to make its physical environment (in particular temperature and chemistry of the atmosphere) on the planet more hospitable to the species which constitute its "life". The Gaia Hypothesis proper defined this "hospitality" as a full homeostasis. A simple model that is often used to illustrate the original Gaia Hypothesis is the so-called Daisyworld simulation.
Recent scientific testing of homeostatic feedbacks involving plankton in Arctic and Antarctic waters, and the effects of rainforests in cloud formation suggest effective regulation of planetary albedo is being compromised by global warming and rainforest destruction.
Whether this sort of system is present on Earth is still open to debate.
Criticism
After initially being largely ignored by scientists, (from 1969 till 1977), thereafter for a period, the initial Gaia hypothesis was ridiculed by some scientists. On the basis of its name alone, the Gaia hypothesis was derided as some kind of neo-Pagan New Age religion. Many scientists in particular also criticised the approach taken in his popular book "Gaia, a New look at Life on Earth" for being teleological;
In 1981, W. Ford Doolittle, in the CoEvolution Quarterly article "Is Nature Motherly" argued that there was nothing in the genome of individual organisms which could provide the feedback mechanisms Gaia theory proposed, and that therefore the Gaia hypothesis was an unscientific theory of a maternal type without any explanatory mechanism.
Stephen Jay Gould criticised Gaia as merely a metaphorical description of Earth processes.
A final criticism leveled against the idea that Gaia is a "living" organism is the fact that the planet has not and is unable to reproduce. Other Gaians have proposed that Gaia is still too young to reproduce and this is not to say that it is conceptually impossible, as humankind may be the means by which Gaia will reproduce. Humanity's exploration of space, its interest in colonizing other planets, and the large body of sci-fi literature that describes terraforming, lend strong evidence to the idea that Gaia is planning to reproduce.
DaisyWorld simulations
Lovelock responded to criticisms with the mathematical Daisyworld model (1983), first to prove the existence of feedback mechanisms, second to demonstrate it was possible that control of the global biomass could occur without consciousness being involved.
Using computer simulations of a hypothetical Daisyworld (with no atmosphere, taking into account only the different albedos of a black and white daisy type) and a mathematical approach, Lovelock and Andrew Watson proved that the controlled stability of the climate was an automatic consequence of the feedback mechanisms that would foster one kind of daisy over another. The Gaia hypothesis had always asserted that Gaia was homeostatic, i.e.
This enables nutrient recycling within a regulatory framework derived by natural selection amongst species, where one being's harmful waste, becomes low energy food for members of another guild. Peter Zvirinsky, The Stimulated Evolution of Biochemical Guilds: Reconciling Gaia Theory with Natural Selection).
The First Gaia Conference
In 1988, to draw attention to the Gaia hypothesis, the climatologist Stephen Schneider organised a conference of the American Geophysical Union's first Chapman Conference on Gaia, held at San Diego in 1989, solely to discuss Gaia.
At the conference James Kirchner criticised the Gaia hypothesis for its imprecision. He claimed that Lovelock and Margulis had not presented one Gaia hypothesis, but four -
CoEvolutionary Gaia - that life and the environment had evolved in a coupled way. Homeostatic Gaia - that life maintained the stability of the natural environment, and that this stability enabled life to continue to exist. Geophysical Gaia - that the Gaia theory generated interest in geophysical cycles and therefore led to interesting new research in terrestrial geophysical dynamics. Optimising Gaia - that Gaia shaped the planet in a way that made it an optimal environment for life as a whole.Of Homeostatic Gaia, Kirchner recognised two alternatives. "Weak Gaia" asserted that life tends to make the environment stable for the flourishing of all life. "Strong Gaia" according to Kirchner, asserted that life tends to make the environment stable, in order to enable the flourishing of all life. Strong Gaia, Kirchner claimed, was untestable and therefore not scientific.
Referring to the Daisyworld Simulations, Kirchner responded that these results were predictable because of the intention of the programmers - Lovelock and Watson, who selected examples which would produce the responses they desired.
Lawrence Joseph in his book "Gaia: the birth of an idea" argued that Kirchner's attack was principally against Lovelock's integrity as a scientist. As Jon Tuney demonstrates, it is not Lovelock's style to respond to such personal attacks and Lovelock did not attack Kirchner's views for ten years, until his autobiography "Hommage to Gaia", where he spoke of Kirchner's sophistry. For example, against the charge that Gaia was teleological Lovelock and Andrew Watson offered the Daisyworld model (and its modifications, above) as evidence against most of these criticisms.
Lovelock was careful to present a version of the Gaia Hypothesis which had no claim that Gaia intentionally or consciously maintained the complex balance in her environment that life needed to survive. It would appear that the claim that Gaia acts "intentionally" was a metaphoric statement in his popular initial book and was not meant to be taken literally. This new statement of the Gaia hypothesis was more acceptable to the scientific community.
The accusations of teleologism were largely dropped after this conference.
An Early Range of views
Some have found James Kirchner's suggested spectrum proposed at the First Gaia Chapman Conference, useful in suggesting that the original Gaia hypothesis could be split into a spectrum of hypotheses, ranging from the undeniable (Weak Gaia) to the radical (Strong Gaia).
Weak Gaia
At one end of this spectrum is the undeniable statement that the organisms on the Earth have radically altered its composition. A stronger position is that the Earth's biosphere effectively acts as if it is a self-organizing system, which works in such a way as to keep its systems in some kind of meta-equilibrium that is broadly conducive to life.
Weak Gaian hypotheses suggest that Gaia is co-evolutive.
The weakest form of the theory has been called "influential Gaia".
The weak versions are more acceptable from an orthodox science perspective, as they assume non-homeostasis. An example is how the activity of photosynthetic bacteria during Precambrian times have completely modified the Earth atmosphere to turn it aerobic, and as such supporting evolution of life (in particular eukaryotic life) . Also such critical theories have yet to explain how conditions on Earth have not been changed by the kinds of run-away positive feedbacks that have affected Mars and Venus.
Biologists and earth scientists usually view the factors that stabilize the characteristics of a period as an undirected emergent property or entelechy of the system; Opponents of this view sometimes reference examples of life's actions that have resulted in dramatic change rather than stable equilibrium, such as the conversion of the Earth's atmosphere from a reducing environment to an oxygen-rich one.
Some go a step further and hypothesize that all lifeforms are part of one single living planetary being called Gaia. In this view, the atmosphere, the seas and the terrestrial crust would be results of interventions carried out by Gaia through the coevolving diversity of living organisms. While it is arguable that the Earth as a unit does not match the generally accepted biological criteria for life itself (Gaia has not yet reproduced, for instance;
Strong Gaia
A version called "Optimizing Gaia" asserts that biota manipulate their physical environment for the purpose of creating biologically favorable, or even optimal, conditions for themselves.
The most extreme form of Gaia hypothesis is that the entire Earth is a single unified organism;
Another strong hypothesis is the one called "Omega Gaia".
Much more speculative versions of Gaia hypothesis, including all versions in which it is held that the Earth is actually conscious or part of some universe-wide evolution (See Selfish Biocosm hypothesis), which is able to make scientifically testable predictions, although it would still be held to be outside the bounds of science, by most thinkers. These are discussed in the Gaia philosophy article. Also outside the bounds of science is the Gaia Movement, a collection of different organisations operating in different countries, but all sharing a concern for how humans might live more sustainably within the "living system".
Recent developments
Gaia Theory has developed considerably In her 1998 book, The Symbiotic Planet, Margulis dedicated the last of the book's eight chapters to Gaia. She resented the widespread personification of Gaia and stressed that Gaia is "not an organism", but "an emergent property of interaction among organisms". She defined Gaia "the series of interacting ecosystems that compose a single huge ecosystem at the Earth's surface. The book's most memorable "slogan" was actually quipped by a student of Margulis': "Gaia is just symbiosis as seen from space". This neatly connects Gaia theory to Margulis' own theory of endosymbiosis.
Both Lovelock's and Margulis's understanding of Gaia are now largely considered valid scientific hypotheses, though controversies continue.
The Second Gaia Conference
By the time of the 2nd Chapman Conference on the Gaia Hypothesis, held at Valencia, in Spain on the 23 June 2000, the situation had developed significantly in accordance with the developing science of Bio-geophysiology. Rather than a discussion of the Gaian teleological views, or "types" of Gaia Theory, the focus was upon the specific mechanisms by which basic short term homeostasis was maintained within a framework of significant evolutionary long term structural change.
The major questions were:
"How has the global biogeochemical/climate system called Gaia changed in time? Can Gaia maintain stability of the system at one time scale but still undergo vectorial change at longer time scales? "What is the structure of Gaia? Are there parts of the system determined pragmatically by whatever disciplinary study is being undertaken at any given time or are there a set of parts that should be taken as most true for understanding Gaia as containing evolving organisms over time? What are the feedbacks among these different parts of the Gaian system, and what does the near closure of matter mean for the structure of Gaia as a global ecosystem and for the productivity of life?" "How do models of Gaian processes and phenomena relate to reality and how do they help address and understand Gaia? Does it matter for Gaia theory whether we find daisies or not?Tyler Volk (1997) has suggested that once life evolves, a Gaian system is almost inevitably produced as a result of an evolution towards far-from-equilibrium homeostatic states that maximise entropy production (MEP). "...the resulting behavior of a biotic Earth at a state of MEP may well lead to near-homeostatic behavior of the Earth system on long time scales, as stated by the Gaia hypothesis." Staley (2002) has similarly proposed "...an alternative form of Gaia theory based on more traditional Darwinian principles...
Gaia hypothesis in ecology
After much initial criticism, a modified Gaia hypothesis is now considered within ecological science basically consistent with the planet earth being the ultimate object of ecological study. Ecologists generally consider the biosphere as an ecosystem and the Gaia hypothesis, though a simplification of that original proposed, to be consistent with a modern vision of global ecology, relaying the concepts of biosphere and biodiversity. The Gaia hypothesis has been called geophysiology or Earth system science, which takes into account the interactions between biota, the oceans, the geosphere, and the atmosphere.
For example the Amsterdam declaration of the scientific communities of four international global change research programmes - the International Geosphere-Biosphere Programme (IGBP), the International Human Dimensions Programme on Global Environmental Change (IHDP), the World Climate Research Programme (WCRP) and the international biodiversity programme DIVERSITAS - recognise that, in addition to the threat of significant climate change, there is growing concern over the ever-increasing human modification of other aspects of the global environment and the consequent implications for human well-being.
They state
"Research carried out over the past decade under the auspices of the four programmes to address these concerns has shown that:
The Earth System behaves as a single, self-regulating system comprised of physical, chemical, biological and human components.These findings would seem to be fully in accord with the Gaia theory. Despite this endorsement, the late Bill Hamilton, one of the founders of modern Darwinism, whilst conceding the empirical basis of the planetary homeostatic processes on which Gaia is based, states that it is a theory still awaiting its Copernicus.
Global warming inevitable
In Lovelock's latest book, The Revenge of Gaia, he argues that because of global warming the world population should brace itself for the inevitable: most of the planet will become uninhabitable by the end of this century (Anon., 2006).
Influence of Gaia Theory outside of Science
At least three works of fiction use the Gaia hypothesis as a central part of the plot. The film Final Fantasy: The Spirits Within, arguably contains a fictional parallel to Sir James Lovelock in the character of Dr. Sid, who is met with skepticism from the scientific and social community when he promotes the idea of a "living Earth".
In Lovelock (1994), a novel by Orson Scott Card &
The Gaia hypothesis was also used as a central theme in the novel Portent, by James Herbert, in which Lovelock is mentioned by name.
In 2006, author Lee Welles wrote the first Award Winning children's book about Gaia. Gaia Girls is a series of seven books about four girls who encounter the living Gaia. Gaia grants them special powers that they must use to her survive the effects of modern humanity. In the first Award Winning book, Gaia Girls: Enter the Earth, Elizabeth Angier helps save Gaia from the ill effects of a gigantic factory pig farm that is moving into her valley. Elizabeth learns about the interconnectedness of all living things on Earth and how we are all a part of the living, breathing Gaia. In November 2006, Gaia Girls - Enter the Earth wins the National Outdoor Book Award.
Maxis has specifically named the Gaia hypothesis and Lovelock as inspirations for their 1990 game, SimEarth.
Fritjof Capra in his fourth book The web of life too has used Gaia theory to explain the complications and interconnections in the marvellous web of life.
Stephan Harding, a student of Lovelock has written a book, Animate Earth: Science, Intuition, and Gaia. Replacing the cold, objectifying language of science with a way of speaking of our planet as a sentient, living being, Harding presents the science of Gaia in everyday English.
The Gameboy Advance RPG Golden Sun and its sequel Golden Sun: The Lost Age propose a similar theory to the Gaia Hypothesis.
Paul Winter composed a "Missa Gaia", which was performed at the Cathedral of Saint John the Divine in New York in the early 1980s.
An oratorio by American composer Nathan Currier called Gaian Variations was premiered on Earth Day 2004 at Lincoln Center by the Brooklyn Philharmonic, using texts of James Lovelock, Loren Eiseley and Lewis Thomas. See also www.gaianvariations.com
The children's cartoon Captain Planet includes the character Gaia as the spirit of Earth.
The popular Japanese anime, Eureka 7, eventually comes to focus on the earth as a living, evolving entity called, "Scab Coral."
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