Ecology: Biology of Interaction. 2.03. The Gaia Hypothesis (Metaphor)

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2.02. Noosphere

D. Shabanov, M. Kravchenko. Ecology: Biology of Interaction Chapter 2. Biospherology

2.04. Biogeochemical Cycles

2.03. The Gaia Hypothesis (Metaphor) Earth is more than just a home; it is a living organism, and we are part of it. James Lovelock As previously noted, regulation via negative feedback is observed at all levels of organization of biosystems. Yet the levels of biosystem organization differ from one another in important respects. An organism, for example, consists predominantly of living tissues, possesses a high degree of integrity, and has a defined set of regulatory subsystems (in animals: the nervous, endocrine, and immune systems). That an organism maintains homeostasis (keeping its essential properties constant) strikes us as entirely familiar. The biosphere, by contrast, consists mainly of non-living components, has no "center" and no regulatory subsystems. And yet it, too, is capable of maintaining the stability of its key parameters! This property of the biosphere made a profound impression on the English chemist James Lovelock, who worked at the American space agency NASA and was attempting to identify the signs by which one might search for planets harboring life. He came to recognize that the most critical parameters of Earth's biosphere (atmospheric composition, the ionic composition of the ocean, climate) are maintained by living organisms in a state far from thermodynamic equilibrium. Over vast stretches of time, Earth's biosphere has sustained conditions favorable to itself on the planet's surface. In 1972, James Lovelock and Lynn Margulis proposed what became known as the "Gaia hypothesis" — the conception of Earth as a superorganism that maintains its own homeostasis. As Lovelock later noted, he and Margulis had independently arrived at ideas previously expressed by James Hutton in the seventeenth century and by Vladimir Vernadsky in the twentieth. Naturally, evaluating this perspective depends greatly on what one understands by the term "superorganism." A naive reading of the concept of hierarchical organization of biosystems leads to the mistaken conclusion that all levels must be structured identically. One need only reflect on the fundamental differences among organisms, populations, communities, and ecosystems to appreciate that a higher level of organization need not resemble a lower one. For this reason alone, the "Gaia hypothesis" is more properly a "Gaia metaphor," in which the planet is compared to an organism. This metaphor is valuable if only because it directs researchers' attention toward the search for mechanisms of planetary regulation. Let us return to the speculative model of global regulation proposed by J. Lovelock in 1979 — "Daisyworld" (see section 1.9). If a biosphere that can do nothing more than alter the color of the petals of flowers growing on its surface is capable of regulating planetary temperature within fairly wide bounds, what then are the capacities of Earth's actual biosphere? The properties of stars of the class to which the Sun belongs are such that they gradually increase their luminosity over time. Over the duration of terrestrial life, this should have led to substantial changes in surface temperatures. Remarkably, this has not occurred. In all likelihood, the relative constancy of climate is the result of the biosphere's regulatory activity. Earth's biosphere is vastly more complex than Daisyworld. Whether adding further components to the model of Daisyworld makes it more or less stable remains a subject of ongoing debate. Many of the interconnections that sustain the functioning of Gaia are still unknown. Let us cite one example discovered with Lovelock's participation. As they die, planktonic algae release gases — dimethyl sulfide and methyl iodide. These gases serve several functions simultaneously. First, they enhance the condensation of water vapor in the atmosphere in the form of clouds. When planktonic algae perish from overheating, the release of these gases leads to the cooling of the water through cloud cover. This effect is not merely local in character. Increased cloud cover raises the planet's albedo — its capacity to reflect incoming solar radiation. The winds generated by cloud cover promote water mixing. In addition, as these gases enter the atmosphere, they enable the return of sulfur and iodine compounds to land, which are essential for terrestrial ecosystems. Increased activity of land plants leads to intensified weathering of rocks and to greater quantities of biogenic nutrients (needed by planktonic algae) entering the ocean via surface runoff. One line of criticism directed at the Gaia concept holds that the stabilization of Earth cannot be linked to differential mortality or differential reproduction of selection units at the planetary level. The purposiveness of organismal-level biosystems is connected to the fact that they differentially (depending on their properties) survive and reproduce. It is clear that no direct analogy with a planetary-level biosystem is possible here. Although planets may perish, they do not reproduce and, still less, transmit to their "offspring" sets of hereditary predispositions that favor their survival and multiplication. "A fatal crack would instantly have opened in Lovelock's hypothesis if he had asked himself at what level of the natural selective process the postulated adaptation of the Earth would have to be evolved. Homeostatic adaptations in individual bodies evolve because individuals with improved homeostatic machinery pass their genes into the future more effectively than those with inferior machinery" (Richard Dawkins). To answer Dawkins's objection, one must probably consider not only the classical Darwinian variant of selection (differential survival and reproduction of organisms) — and certainly not its extension to the genetic level corresponding to the "selfish gene" concept (i.e., differential replication of genetic sequences). As Ludwig Boltzmann indicated, the concept of natural selection carries a very broad physical meaning. The second law of thermodynamics, to the elaboration of which Boltzmann made outstanding contributions, can be formulated, among other ways, as follows: open systems spontaneously transition to more stable (more probable) states. Stability in the general sense, as you will recall, is the capacity of a system to maintain its state. One consequence of this formulation of the second law of thermodynamics may appear to be a rather simple thought, fully consistent with common sense. Yet it opens the way for the explanation of many non-trivial phenomena; it is this: processes that stably maintain their state and are capable of self-perpetuation displace unstable and less readily propagating processes. Natural selection is one of a series of examples in which unstable processes are displaced by stable ones. Of course, we are accustomed to thinking of organisms as discrete units, but this is a matter of habit. Despite the fact that we usually perceive organisms as relatively permanent structures, they can (and in some cases must) be viewed as transient states arising in the course of specific processes — life cycles, sequences of ontogenies (Fig. 2.3.1). "What is called structure is a slow process of long duration; what is called function is a rapid process of short duration" (Ludwig von Bertalanffy). [IMG_1] Fig. 2.3.1. Organisms are not independent units. Each is part of a process of reproduction of a specific life cycle. Only those processes that proved stable are accessible to our observation. In accordance with the foregoing, classical Darwinian selection can also be described as follows. Among variable units capable of reproducing their own kind, those that are better preserved and reproduced persist over time. However, the units subject to selection for stability need not be only individual systems; they may also be specific states of a single system. In the evolution of the biosphere, we observe changes in processes occurring at a level lower than the biospheric. Some of these processes are stable; others are not. Succession (see section 3.8), for instance, occurs because the existence of unstable communities is transient, and in time they are replaced by stable (climax) ones — until some perturbation deprives them of their stability. The authors of this textbook propose that planetary regulatory mechanisms may arise and be refined through competition among alternative processes at the biocoenotic level (Fig. 2.3.2). Unfortunately, the degree to which such competition has been studied remains clearly insufficient. [IMG_2] Fig. 2.3.2. More stable processes displace less stable ones. This may be the reason for the evolution of planetary regulatory mechanisms. In any event, the Gaia hypothesis interweaves elements of scientific theory with elements of religious prophecy. In recent years, James Lovelock has put forward predictions of catastrophe. He regards humanity as the "nervous system" of Gaia, through which she becomes conscious of herself. Alas, humanity has failed to recognize its role and has disrupted the functioning of Gaia. "Gaia has made me a planetary physician, and since I take my profession seriously, I am obliged to report bad news. ... Climate research centers throughout the world — constituting the equivalent of a diagnostic laboratory or hospital, reporting on the physical condition of the Earth — show that specialists see the planet as gravely ill, and that in the very near future it will develop a fever lasting no less than 100,000 years. And I must tell you, members of the Earth family, and its closest part, that you, and civilization in particular, are in mortal danger. ... We must be the heart and mind of the Earth, not merely a viral disease. So let us gather the courage to think not only about the needs and rights of humanity, but also about the harm we have inflicted upon the Earth and how we may be reconciled with Gaia. We must take action while we are still strong enough to do so, while we are not yet a wretched multitude of people broken by the cruel will of savage military dictators. The most important thing we must remember is that we are part of the Earth, and that it is indeed our home" (J. Lovelock). An intriguing development of the Gaia metaphor is the Medea metaphor, proposed by the American paleontologist Peter Ward. Medea is a figure from ancient Greek mythology, the wife of Jason, who killed her own children. The point is that the mass extinctions in the history of terrestrial life can be viewed as regulatory interventions by the planet upon its biota. Unfortunately, we must seriously consider the scenario in which humanity drives the biosphere into an unstable state and thereby ceases to exist. Planetary and biospheric responses to such human activity, ultimately leading to the destruction of humanity, can be interpreted within the framework of the Medea metaphor — Medea destroying her own children. Whatever one's view of the Gaia hypothesis, one cannot but agree with Lovelock that one of the principal parameters of the biosphere is the concentration of CO2 in the atmosphere. The problems raised by Lovelock likely merit serious study. One effective method of such study, in the opinion of the authors of this textbook, may be simulation modeling. Ukrainian / Russian

2.02. Noosphere

Ecology: Biology of Interaction Chapter 2. Biospherology

2.04. Biogeochemical Cycles