The modern roots of psychology can be traced back to the 17th century when the idea of an immaterial "mind" (or spirit or "thinking I"), immune from the laws of physics, was advanced by Descartes as part of the dualistic world view that gained ascendancy along with the Scientific Revolution. At the point of this conceptual origin, psychology can thus be seen as the study of all that is not physical. Because the "matter" of the physical world was taken by Descartes to be composed of purposeless, reversible, analytically continuous, and quality-less particles (without color, taste, or smell) governed by deterministic law, the lion's share of worldly properties was clearly left to the immaterial or "mental" portion of the world. Although philosophy became historically separated from psychology as the discipline whose job it was to address ontological and epistemo logical problems (generated, largely, by the inherent incommensurability of the Cartesian schem ' e itself), this separation has always been fuzzy at best because from the time of Descartes psychological arguments (in particular, theories of perception) were almost invariably used, or assumed, as the starting point for epistemological and ontological claims.
While Descartes saw the entire natural world, including "organic nature" (with the exception of the immaterial mind of humans), as a giant deterministic machine, Kant (1790/1929), taking the view that it was impossible for the purposiveness of living things to be described in mechanical terms, argued for the "autonomy of biology" from physics (Cassirer, 1940/1950). Although, like Descartes, Kant had formulated his argument to serve his own transcendental doctrine, his criticism of mechanism was entirely correct. The consequence of his "autonomy of biology" argument, however, was the establishment of a new dualism-a dualism of life versus physics (living vs. nonliving or organism vs. environment). This same argument, of the incommensurability of physics and the characteristic properties of living things (to strive, perceive, and act purposively), is still used in contemporary science to back the case for a biology largely indifferent to the general principles of physics (e.g., Mayr, 1985).
The fundamental mutuality claim of ecological psychology (Gibson, 1979/1986), that living things as perceiver-actors and their environments constitute single and irreducible dynamical systems (Mace, 1977; Turvey & Carello, 1981), rejects the traditional view that the properties of living things and physical law are incommensurable. Recent work by Swenson (1988, 1989b, 1989c, 1989e, in press-b) on the thermodynamics of self-organizing systems, when coupled with the law-based account of information in the specificational sense (Gibson, 1966, 1979/1986; Kugler & Turvey, 1987), shows how the active, end-directed behavior of living things has its origins in the symmetry properties of physical law and how the mutuality claim of ecological psychology can be shown to directly follow. While a number of the central themes of this article are laid out in detail, many others can only be sketched. A more complete development will be presented in a subsequent work (Swenson, in press-d).

Thermodynamics and Perception-Action Cycles

From a thermodynamic point of view, animals move so that they can eat, and eat so that they can move (lberall, 1974). Form and function demand a continuous production of entropy (degradation of energy), and to preserve form and function, therefore, an animal's on-board energy supply must be regularly replenished. Although many living things have their fuels served to them, animals by and large must service themselves; they move so they can eat.
From a different point of view, which takes as its focus the perceptual capabilities of animals, one might say that animals move so that they can perceive, and perceive so that they can move (Gibson, 1979/1986). As underscored by Gibson (1966), the commonplace, directed behaviors of animals comprise continuous cyclic relations between the detection of information and the performatory and exploratory activities that serve, in significant part, to facilitate that detection and which, in turn, are guided and shaped by it. In a wedding of the perceptionist's view with that of the thermodynamicist, perception-action cycles are seen as supporting the self servicing that maintains an animal's on-board potential at appropriate levels. The perceptual guidance of movements and the movement enhancement of opportunities to perceive, extend to animals particular benefits in their search for, and consummation of, energy resources.
Clearly, perception-action cycles can be placed into a thermodynamic perspective, as the foregoing attests: Perceiving and acting capabilities are what they are, in part because the thermodynamical requirements of living things are what they are. The emphasis of this rationalization -of perception steering actions and actions amplifying perceptual opportunities-is on "energy replenishment" or "acquisition of energy resources." It is an emphasis that draws on an indirect connection between thermodynamics and perception-action cycles. The second law of thermodynamics is about the production of entropy -about the dissipation of energy resources, not their replenishment. The argument advanced in this article is that perception-action cycles have a much deeper and more direct connection with thermodynamic principles. That is, perception-action cycles are what they are because they extend the means for dissipating energy resources, for enhancing the rate of environmental entropy production.

Respiration Intensity and Atmospheric Oxygen

The study of global evolution reveals the amplification of biospheric entropy production with the growth and differentiation of living matter over geological time. The increase in atmospheric oxygen shown in Figure I characterizes a progressive departure of the global Earth system (as a single planetary entity) away from equilibrium, The transformation of the redox state of the planetary system, from reducing when life first appeared some 3.8 billion years ago (GYA-i.e., giga years ago) to mildly oxidative some 2 GYA to its presently highly oxidative state, is a measure of a progressive ordering or internal entropy reduction of the planetary system as a whole. Given the balance equation dictated by the second law, this progressive increase of order is also a measure of an increasing rate of entropy production for the geo-cosmic field: Local reductions of entropy in a field (the local production and maintenance of order) necessarily increase its rate of entropy production (the rate at which it minimizes its potentials).
Because the atmosphere on the Archean Earth when life emerged was mildly reducing, life is presumed to have had an anaerobic beginning. That is, it was essentially fermenting and limited by the availability of abiogenically formed organic compounds. The first photosynthetic bacteria (presumed to be similar to extant purple and green bacteria) provided the means by which the production of life was linked directly to the sun (solar source) by using many of the incompletely metabolized waste products of the fermenters as well as outgassed reduced compounds from volcanic emissions such as hydrogen sulfide and sulfur for reducing power (as electron sources). Expansion was now limited by the availability of these ready-macle hydrogen compounds. The water (H20) on Earth provided an almost unlimited source of electrons, but the original photosynthesizers could not muster the energy to split the water molecules.
About 3.5 GYA proto-cyanobacteria (ancestors of contemporary cyanobacteria that were formerly called blue-green algae) learned to link two light sinks (light-trapping systerns) together so as to apply the necessary two photons to the cleavage of one water molecule. The result was the linking of the virtually unlimited supply of photons from the sun to the virtually unlimited supply of electrons in water and the release of oxygen (02) into the atmosphere. In consequence, along with a massive acceleration in the expansion of life, the Pre-Phanerozoic (the "Pre-Cambrian" in the ealier literature) bore witness to a buildup of atmospheric 02 and a shifting of the planetary redox potential from reducing to oxidative. Before this global bifurcation could occur, however, natural reservoirs -chemical elements such as sulfur and iron that combine readily with 02 -acting as 02 sinks had to be filled. The biogeochemical evidence for this occurring approximately 2 GYA includes the abrupt termination of the formation of banded-iron formations, the appearance of continental redbeds, and the disappearance of thorium-rich uraninite and pyrite (Cloud, 1976, 1988). When the sinks were filled, the availability Of 02 in the atmosphere produced a chemical potential providing the opportunity for an even greater production of living matter. Whereas anaerobic fermentation of one mole of glucose to lactic acid produces a flux of 56,000 calories of free energy, the complete oxidation of the same amount of glucose to carbon dioxide and water produces a flux of 686,000 calories.

ecological psychology: the increase of atmospheric oxygen over evolutionary time

FIGURE 1 Buildup of atmospheric O2 in geological time (PAL is present atmospheric level.) From "Engineering Initial Conditions in a Self-Producing Environment" by R. Swenson, in M. Rogers and N. Warren (Eds.) A Delicate Balance: Technics, Culture and Consequences (p. 71), 1989d, Los Angeles Institute of Electrical and Electronic Engineers (IEEE). Copyright 1989 by IEEE. Reprinted by permission. Data originally fro Cloud (1976) and Runnegar (1982).

The opportunistic production of increasingly more highly ordered states as a function of increasing planetary 02 is shown in Figure 1. Thus, the buildup of atmospheric 02 can be seen not only as a measure of the distance of the planetary system from equilibrium, but as the buildup of an internal potential that operated over evolutionary time as an internal amplifier driving the planetary system even further from equilibrium. Figure 2 unpacks this thermodynamic scenario still more: It shows that not only does terrestrial entropy production increase as the result of the increase in the quantity of order or living matter over geological time, but so does the intensity of entropy production or mass specific entropy production. In fact, as the discussion above indicates, this property to expand both qualitatively (nonlinearly) and quantitatively (linearly) has been characteristic of life from its beginnings.

ecological psychology: increase in planetary mass specific respiration intensity

FIGURE 2 Growth of specific respiration intensity as a function of geological time. From "Bioenergetic Trends of Evolutionary Progress of Organisms" by A. Zotin, in I Lamprecht and a.I. Zotin (Eds.), Thermodynamics and Regulation of Biological Processes (p.453), 1984, Berlin: Walter de Gruyter. Copyright 1984 by Walter de Gruyter. Reprinted by permission.

Specifically, Figure 2 depicts the respiration intensity per unit mass of living things as a function of the Earth's last 600 million years (MY). Aerobic respiration (oxidative phosphorylation) is the process by which living things employ 02 to release the energy potential from their food. 02 is used to "burn up" or oxidize food in the same manner that 02 is used in the burning of a flammable material to produce fire. In aerobic respiration, one molecule Of 02 iS used for the conversion of each atom of organic carbon. The mass specific respiration intensity is the rate at which chemical resources are dissipated or burned by 02 into waste or heat products per unit mass of body weight. It is thus a measure of the specific or per-unit-mass rate of entropy production. Taken together, Figures I and 2 reveal the global nature of evolutionary ordering: Higher order states require higher rates of dissipation to maintain their extension; the increase in atmospheric oxygen over evolutionary time provided the potential required for progressively higher ordered states (the steep increase in the respiration intensity function [Figure 21 corresponds to the steep increase in the buildup of atmospheric 02 [Figure l]; the higher order states act as sinks that dissipate the potential.
A well-recognized fact is that for a living thing to exist it must add continuously to the universal level of entropy (e.g., Schr6dinger, 1945). A much less well-recognized fact is conveyed by Figures I and 2, namely, that when considered at a planetary scale and in geological time, the expansion and differentiation of living matter through the production of more and more living things has increased the mass specific planetary rate of entropy production. The insight made famous in Schr6dinger's statement "Life feeds on negentropy," and first put forward by Bertalanffy (1952), is that living things are not equilibrium states but rather steady states maintained away from equilibrium by a continuous flow of energy and matter. To be a living thing implies converting energy into organization and doing so ceaselessly, and thus the order defining a living thing continuously adds to the universal entropy; what Figure I highlights is that with the production of more order, with more numerous and more richly organized living things, and with the progressive production of higher states of order, the additions to the universal entropy are made at a greater rate. The insight conveyed by Schr6dinger's statement now seems too static given Figures I and 2, which show the opportunistic emergence of order as a function of the evolutionary increase of atmospheric 02. Schr6dinger's insight is mute with respect to the directed nature of life as an opportunistic planetary process of self-organization characterized by progressive differentiation and complexification. Conjointly, Figure I and Figure 2 supply a potentially more encompassing insight: Life proliferates horizontally (increase in number) and vertically (increase in levels of order) because the rate of entropy production is thereby increased. It is this insight that provides the context for inquiring about the thermodynamic status of perception-action cycles.
To summarize, Figures 1 and 2 suggest (a) the impossibility of conceiving of living things as separate from their surrounds, (b) that both together are part of a directed single planetary or global evolutionary process or entity, and (c) that this direction is characterized by an opportunistic strategy that produces progressively more ways, and more intense ways, for this global system to generate entropy (first prokaryotes fermented naturally forming organic compounds on an anaerobic Earth; then "bacterial photosynthesizers" hooked solar energy directly to terrestrial sinks [to incompletely metabolized products of fermenters and outgassed reduced compounds] and produced organic matter directly; then proto-cyanobacteria discovered how to hook solar energy to the unlimited electron supply in water, thus also releasing 02 into the atmosphere; and the consequent atmospheric 02 provided the chemical potential to burn organic matter faster [oxidative metabolism] and produce progressively more highly ordered forms). It will be assumed that suggestions (a), (b), and (c), are pivotal to the thermodynamic rationalization of perception-action cycles.

A Physical Strategy

The perceptual guidance of movements and the movement enhancement of opportunities to perceive comprise a prominent aspect of the functional order at the ecological scale, the scale at which living things and their environments are defined. An argument is to be developed that the origins of perception-action cycles inhere in the second law of thermodynamics and are addressable through the concepts needed for understanding the phenomena depicted in Figures I and 2. In addressing such issues, Aristotle's methodology (without his explanations) is brought to bear: To arrive at an understanding of the nature of a thing, ask the ends that are served. Specifically, the strategy needed to understand perception-action cycles is the physical strategy of identifying the preceding generalized "field conditions" that produced or selected them at their origins and have continued to produce and progressively select them as viable states of dynamical order over evolutionary time.