Geophysiology (Geo, earth + physiology, the study of living bodies) is the study of interaction among living organisms on the Earth operating under the hypothesis that the Earth itself acts as a single living organism (Gaia).
The term "geophysiology" was popularized by James Lovelock in his writings on the Gaia hypothesis. The term was in fact foreshadowed by many others. James Hutton (1726-1797), the "Father of Geology" in 1789, in a lecture presented on his behalf by Dr. Black, wrote "I consider the Earth to be a super-organism and that its proper study should be by physiology." This view that the Earth in some ways could be viewed as a superorganism was widely held in the early 19th century, and was supported even by such early biologists as Huxley (1825-1895). An analogous alternative geophysiology which views the Earth as a single cell was developed by Lewis Thomas in his The Lives of a Cell: Notes of a Biology Watcher (1974).
Vladimir Vernadsky (1863-1945), founder of biogeochemistry suggested that geophysiological processes were responsible for the development of the Earth through a succession of phases in which the geosphere (of inanimate matter) develops into the biosphere (of biological life). Vernadsky's thinking significantly influenced the development of ecology in Russia, culminating in the "Russian Paradigm" (a term first coined by Georgii A. Zavarzin in 1995). The basic tenets of this approach are i) that life can only exist in the form of interconnected nutrient cycles (i.e. the ecosystem); ii) that ecosystem assembly is an organized process as opposed a haphazard one; iii) that the emergence of life on earth was congruent with respect to the appearance of primordial nutrient cycles; iv) that in addition to the evolution of species there exists a separate process of ecological evolution the direction of which is predetermined by community composition and dynamics (Lekevičius, 2006).
Frederick Clements (1874-1945) of the Carnegie Institute of Washington, who popularized the idea of vegetation climax also introduced the idea of physiology to ecology, considering the interlocking natures of plants and animals as metabolic processes within a single superorganism.
The British biologist, Arthur Tansey (1871-1955), who introduced the term ecosystem, also considered the possibility that plant communities could be considered to be boundary-less quasi-organisms, although he never extended his ideas to a planetary scale.
G. Evelyn Hutchison, studied the way logistic growth, biological feedback systems and self-regulation tended to explain many of the features of ecological systems, and Raymond Lindeman has further extended the way energy flows between various trophic levels in his "trophic-dynamic" model, further developed by Mark McMenamin and Dianna McMenamin's thesis of "Hypersea", which looks at the rate of water flow through the Gaian biological environment. Tyler Volk, has also looked at the trophic cycling of various elements upon which life depends, and argues that this is central to an understanding of geophysiology.
Eugene Odum believed that homeostasis and stability in ecosystems was a result of evolutionary processes, and Howard Odum (his brother) extended this work to include thermodynamic effects in producing ecological "steady states". Howard Odum also extended the nature of the scale of ecosystems from that of a single pond upwards, showing that a "nested hierarchy", "heterarchy" or "holarchy" existed in which systems could be considered as elements of larger systems (leaf to tree to glade to forest to bioregion to biotic realm or biomes). On the basis of this, Gaia theory and geophysiology represent the ultimate extension of these principles.