International Encyclopedia of Systems and Cybernetics

The hypothesis according to which the Earth, as a planet, is a global adaptive and regulated system, in permanent evolution as a result of the interactions between its physical and living components.

This hypothesis has been presented in 1979 by J. LOVELOCK. In his view, GAIA is "… a complex entity involving the Earth's biosphere, atmosphere, oceans and soil; the totality constituting a feedback or cybernetic system which seeks an optimal physical and chemical environment for life on this planet. The maintenance of relatively constant conditions by active control may be conveniently described by the term "homeostasis" (1979, p.11). LOVELOCK writes that his hypothesis: "is in contrast to the conventional wisdom which held that life adapted to the planetary conditions, as it and they evolved their separate ways" (p.152).

Earth homeostasis could possibly be accepted in the very general cosmic sense, as an evolutive celestial body that maintains an oscillating global equilibrium within the solar system. However GAIA itself evolves. As observed by I. PRIGOGINE and P.M. ALLEN: "… the Earth is not in thermodynamic equilibrium and… the flow of solar energy in which it is bathed is sufficient to ensure that for the systems of interest the relevant thermodynamic regime is not that of equilibrium, or of near equilibrium, but rather that of far-from-equilibrium" (1982, p.6).

GAIA hypothesis has generated a considerable current of diverging opinions (See for ex. T. BEARDSLEY – Scientific American, Dec. 1989, p.35-6). Until now, the debate remains open.

To confront all this criticism and in collaboration with A.J. WATSON, LOVELOCK has created "Daisy World", a model meant to justify his hypothesis (1983).

The GAIA hypothesis could possibly be compared with LOTKA's world engine concept.

More recently P. BAK emitted the following opinion: "One might think of self-organized criticality as the general, underlying theory for the Gaia hypothesis. In the critical state the collection of species represents a single coherent organism following its own evolutionary dynamics. A single triggering event can lead an arbitrary large fraction of the ecological network to collapse, and eventually be replaced by a new stable ecological network. This would be a "mutated" global organism. At the critical point, all species influence each other. In this state they act collectively as a single meta-organism, many sharing the same fate. This is highlighted by the very existence of large-scale extinctions… Within the self-organized criticality picture, the entire ecology has evolved into the critical state" (1996, p.155-6)