Gaia theory science: Encyclopedia II - Gaia theory science - Critical analysis

Gaia theory science - Critical analysis

Gaia theory science - 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.

Whether this sort of system is present on Earth is still open to debate. Some relatively simple homeostatic mechanisms are generally accepted. For example, when atmospheric carbon dioxide levels rise, plants are able to grow better and thus remove more carbon dioxide from the atmosphere, but the extent to which these mechanisms stabilize and modify the Earth's overall climate are not yet known.

Gaia theory science - Criticism

The initial Gaia Hypothesis was highly criticized by many scientists for being teleological, a belief that all things have a predetermined purpose.

It was very critically received, in particular by Richard Dawkins and Ford Doolittle. These latter argue organisms could not act in concert as this would require foresight and planning from them. They rejected the possibility that feedback loops could stabilize the system. In 1982, Dawkins claimed "there was no way for evolution by natural selection to lead to altruism on a Global scale". They find it impossible to see how the feedback loops which Lovelock says stabilise the Gaian system could have evolved. They argue that, as Gaia can't reproduce herself, she cannot be alive in any meaningful sense. They also claim that the theory is not scientific because it is impossible to test it by controlled experiment. Lovelock offered the Daisyworld model as mathematical evidence to refute most of these criticisms.

The initial hypothesis was rather imprecise, and Lovelock later refuted accusation of teleologism by stating "Nowhere in our writings do we express the idea that planetary self-regulation is purposeful, or involves foresight or planning by the biota." – (Lovelock, J. E. 1990)

Gaia theory science - 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.

More recently, studies of artificial life using various guilds, of photosynthesisers, herbivores, carnivores, scavengers and decomposers, enables nutrient recycling within a regulatory framework derived by natural selection amongst species, where one being's harmful waste, becomes high energy food for members of another guild. This research on te Redfield Ratio of Nitrogen to Phosphorus, shows that local biotic processes can regulate global systems (See Keith [Downing] & Peter Zvirinsky, The Stimulated Evolution of Biochemical Guilds: Reconciling Gaia Theory with Natural Selection).

Gaia theory science - The First Gaia Conference

In 1988, the climatologist Stephen Schneider organised a conference of the American Geophysical Union solely to discuss Gaia. The accusations of teleologism were dropped after that meeting.

Lovelock presented a new version of the Gaia Hypothesis, which abandoned any attempt to argue that Gaia intentionally or consciously maintained the complex balance in her environment that life needed to survive. This new hypothesis was more acceptable by the scientific community. He supported his new hypothesis with the metaphor of Daisyworld. Using computer simulations of the Daisyworld parameters (no atmosphere, taking into account different albedos for each daisy type) and a mathematical approach, Lovelock proved that the controlled stability of the climate by life was not being teleological. The new Gaia hypothesis stated that Gaia was homeostatic, i.e. that the biota influence the abiotic world in a way that involves homeostatic feedback.

During the Gaia conference, James Kirchner, a physicist and philosopher took the opportunity of the meeting to explain that there are not one Gaia hypothesis, but several ones ranging from "weak Gaia" to "strong Gaia". He then described five of these: Influential Gaia, Coevolutionary Gaia, Homeostatic Gaia, Teleological Gaia, Optimizing Gaia.

Gaia theory science - Strong Gaia theories

Several types of strong theories may be defined.

An even stronger claim states that biota manipulate their physical environment to create optimal conditions. It is sometimes referred to as optimizing Gaia.

Optimizing Gaia asserts that the biota manipulate their physical environment for the purpose of creating biologically favorable, or even optimal, conditions for themselves.

Another strong theory is the one called Omega Gaia. Teilhard de Chardin claimed that the Earth is evolving through stages of cosmogenesis, affecting the geosphere, biogenesis of the biosphere, and noogenesis of the noosphere, culminating in the Omega Point.

A version of Gaia theory was developed by Lynn Margulis, a microbiologist who won the MacArthur Award for the Endosymbiosis Theory, in 1979. Her model is in some ways more limited in scope than the one that Lovelock proposed. In particular, that only homeorhetic and not homeostatic balances are involved, and that there is no special tendency of biospheres to preserve their current inhabitants, and certainly not to make them comfortable. 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. But this is true of all multicellular organisms, not all cells in the body die instantaneously.

Coauthor of the original Gaia Hypothesis, "Lynn Margulis, tells us that Earth is not homeostatic but homeorhetic: 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... Gaia is just symbiosis as seen from space." – from Greenpeace apparently in reference to Lynn Margulis, Symbiotic Planet: A New View of Evolution.

A system in homeostasis tends to move towards constant values for its parameters, whereas a system in homeorhesis will always exhibit similar dynamic behavior, without necessarily converging to a constant state. There is strong evidence that plants are selected for the microclimate effects which they can have locally to themselves, and good evidence that these patterns also exist on some wider scales, with symbiotic relationships existing for larger scale climate modification.

Other reductionist theories suggest that Gaia is co-evolutive. Co-evolution in this context has been thus defined: "Biota influence their abiotic environment, and that environment in turn influences the biota by Darwinian process." Lovelock gave evdence of this in his second book "The Ages of Gaia", showing the evolution from the world of the early thermo-acido-phyllic and methanogenic bacteria towards the oxygen enriched atomsphere today that permits more complex life.

The weakest form of the theory has been called influential Gaia. It barely states that biota influence certain aspects of the abiotic world, e.g. temperature and atmosphere.

All of these theories are more acceptable from an orthodox science perspective, as they assume non-homeostasis. They state the evolution of life and its environment may affect each other. 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) . However, these theories do not claim the atmosphere modification has been done in coordination and through homeostasis.

Gaia theory science - Semantic debate

The argument is that these symbiotic organisms, being unable to survive apart from each other and their climate and local conditions, form an organism in their own right, under a wider conception of the term organism than is conventionally used. It is a matter for often heated debate whether this is a valid usage of the term, but ultimately it appears to be a semantic dispute. In this sense of the word organism, it is argued under the theory that the entire biomass of the Earth "is a single organism".

Unfortunately, many supporters of the various Gaia theories do not state exactly where they sit on this spectrum; this makes discussion and criticism difficult. More recently after other conferences the whole spectrum of "weak" and "strong Gaia" itself has been called into question.

Much effort on behalf of those analyzing the theory currently is an attempt to clarify what these different hypotheses are, and whether they are proposals to "test" or "manipulate" outcomes. Both Lovelock's and Margulis's understanding of Gaia are considered valid scientific theories, and are now a part of biology proper.

Adapted from the Wikipedia article "Critical analysis", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki