fies the domain of the network s operations and defines the system as a unit. The authors point out that catalytic cycles, in particular, do not constitute living systems, because their boundary is determined by factors (such as a physical container) that are independent of the catalytic processes.
It is also interesting to note that physicist Geoffrey Chew formulated his so-called bootstrap hypothesis about the composition and interactions of subatomic particles, which sounds quite similar to the concept of autopoiesis, about a decade before Maturana first published his ideas. 55 According to Chew, strongly interacting particles, or “hadrons,” form a network of interactions in which “each particle helps to generate other particles, which in turn gen-
. * 4 . ”54 °
erate it.
However, there are two key differences between the hadron bootstrap and autopoiesis. Hadrons are potential “bound states” of each other in the probabilistic sense of quantum theory, which does not apply to Maturana’s “organization of the living.” Moreover, a network of subatomic particles interacting through high- energy collisions cannot be said to be autopoietic because it does not form any boundary.
According to Maturana and Varela, the concept of autopoiesis is necessary and sufficient to characterize the organization of living systems. However, this characterization does not include any information about the physical constitution of the system’s components. To understand the properties of the components and their physical interactions, a description of the system’s structure in the language of physics and chemistry must be added to the abstract description of its organization. The clear distinction between these two descriptions—one in terms of structure and the other in terms of organization—makes it possible to integrate structure-oriented models of self-organization (such as those by Prigogine and Haken) and organization-oriented models (as those by Eigen and Maturana-Varela) into a coherent theory of living systems. 55
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Gaia—the Living Earth
The key ideas underlying the various models of self-organizing systems just described crystallized within a few years during the early 1960s. In the United States Heinz von Foerster assembled his interdisciplinary research group and held several conferences on self-organization; in Belgium Ilya Prigogine realized the crucial link between nonequilibrium systems and nonlinearity; in Germany Hermann Haken developed his nonlinear laser theory and Manfred Eigen worked on catalytic cycles; and in Chile Humberto Maturana puzzled over the organization of living systems.
At the same time, the atmospheric chemist James Lovelock had an illuminating insight that led him to formulate a model that is perhaps the most surprising and most beautiful expression of selforganization—the idea that the planet Earth as a whole is a living, self-organizing system.
The origins of Lovelock’s daring hypothesis lie in the early days of the NASA space program. While the idea of the Earth being alive is very ancient and speculative theories about the planet as a living system had been formulated several times, 56 the space flights during the early 1960s enabled human beings for the first time to actually look at our planet from outer space and perceive it as an integrated whole. This perception of the Earth in all its beauty—a blue-and-white globe floating in the deep darkness of space—moved the astronauts deeply and, as several have since declared, was a profound spiritual experience that forever changed their relationship to the Earth. 57 The magnificent photographs of the whole Earth that they brought back provided the most powerful symbol for the global ecology movement.
While the astronauts looked at the planet and beheld its beauty, the environment of the Earth was also examined from outer space by the sensors of scientific instruments, and so were the environments of the moon and the nearby planets. During the 1960s the Soviet and American space programs launched over fifty space probes, most of them to explore the moon but some traveling beyond to Venus and Mars.
At that time NASA invited James Lovelock to the Jet Propulsion Laboratories in Pasadena, California, to help them design instruments for the detection of life on Mars. 58 NASA’s plan was to send a spacecraft to Mars that would search for life at the landing site by performing a series of experiments with the Martian soil. While Lovelock worked on technical problems of instrument design, he also asked himself a more general question: How can we be sure that the Martian way of life, if any, will reveal itself to tests based on Earth’s lifestyle? Over the following months and years this question led him to think deeply about the nature of life and how it could be recognized.
In contemplating this problem, Lovelock found that the fact that all living organisms take in energy and matter and discard waste products was the most general characteristic of life he could identify. Much like Prigogine, he thought that one should be able to express this key characteristic mathematically in terms of entropy, but then his reasoning went in a different direction. Lovelock assumed that life on any planet would use the atmosphere and oceans as fluid media for raw materials and waste products. Therefore, he speculated, one might be able, somehow, to detect the existence of life by analyzing the chemical composition of a planet’s atmosphere. Thus if there was life on Mars, the Martian atmosphere should reveal some special combination of gases, some characteristic “signature” that could be detected even from Earth.
These speculations were confirmed dramatically when Lovelock and a colleague, Dian Hitchcock, began a systematic analysis of the Martian atmosphere, using observations made from Earth, and compared it with a similar analysis of the Earth’s atmosphere. They discovered that the chemical compositions of the two atmospheres are strikingly different. While there is very little oxygen, a lot of carbon dioxide (C0 2 ), and no methane in the Martian atmosphere, the Earth’s atmosphere contains massive amounts of oxygen, almost no C0 2 , and a lot of methane.
Lovelock realized that the reason for that particular atmospheric profile on Mars is that on a planet with no life, all possible chemical reactions among the gases in the atmosphere were completed a long time ago. Today no more chemical reactions are
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possible on Mars; there is complete chemical equilibrium in the Martian atmosphere.
The situation on Earth is exactly the opposite. The terrestrial atmosphere contains gases like oxygen and methane, which are very likely to react with each other but coexist in high proportions, resulting in a mixture of gases far from chemical equilibrium. Lovelock realized that this special state must be due to the presence of life on Earth. Plants produce oxygen constantly and other organisms produce other gases, so that the atmospheric gases are being replenished continually while they undergo chemical reactions. In other words, Lovelock recognized the Earth’s atmosphere as an open system, far from equilibrium, characterized by a constant flow of energy and matter. His chemical analysis identified the very hallmark of life.
This insight was so momentous for Lovelock that he still remembers the exact moment when it occurred:
For me, the personal revelation of Gaia came quite suddenly—like a flash of enlightenment. I was in a small room on the top floor of a building at the Jet Propulsion Laboratory in Pasadena, California. It was the autumn of 1965 . . . and I was talking with a colleague, Dian Hitchcock, about a paper we were preparing. . . . It was at that moment that I glimpsed Gaia. An awesome thought came to me. The Earth’s atmosphere was an extraordinary and unstable mixture of gases, yet I knew that it was constant in composition over quite long periods of time. Could it be that life on Earth not only made the atmosphere, but also regulated it—keeping it at a constant composition, and at a level favorable for organ-
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The process of self-regulation is the key to Lovelock’s idea. He knew from astrophysics that the heat of the sun has increased by 25 percent since life began on Earth and that, in spite of this increase, the Earth’s surface temperature has remained constant, at a level comfortable for life, during those four billion years. What if the Earth were able to regulate its temperature, he asked, as well as other planetary conditions—the composition of its atmosphere, the salinity of its oceans, and so on—just as living organ-
isms are able to self-regulate and keep their body temperature and other variables constant? Lovelock realized that this hypothesis amounted to a radical break with conventional science:
Consider Gaia theory as an alternative to the conventional wisdom that sees the Earth as a dead planet made of inanimate rocks, ocean, and atmosphere, and merely inhabited by life. Consider it as a real system, comprising all of life and all of its environment tightly coupled so as to form a self-regulating entity. 60
The space scientists at NASA, by the way, did not like Lovelock s discovery at all. They had developed an impressive array of life-detection experiments for their Viking mission to Mars, and now Lovelock was telling them that there was really no need to send a spacecraft to the red planet in search of life. All they needed was a spectral analysis of the Martian atmosphere, which could easily be done through a telescope on Earth. Not surpris- ingly, NASA disregarded Lovelock’s advice and continued to develop the Viking program. Their spacecraft landed on Mars several years later, and as Lovelock had predicted, it found no trace of life.
In 1969, at a scientific meeting in Princeton, Lovelock for the first time presented his hypothesis of the Earth as a self-regulating system. 61 Shortly after that a novelist friend, recognizing that Lovelock’s idea represents the renaissance of a powerful ancient myth, suggested the name “Gaia hypothesis” in honor of the Greek goddess of the Earth. Lovelock gladly accepted the suggestion and in 1972 published the first extensive version of his idea in a paper titled “Gaia as Seen through the Atmosphere.” 62
At that time Lovelock had no idea how the Earth might regulate its temperature and the composition of its atmosphere, except that he knew that the self-regulating processes had to involve organisms in the biosphere. Nor did he know which organisms produced which gases. At the same time, however, the American microbiologist Lynn Margulis was studying the very processes Lovelock needed to understand—the production and removal of gases by various organisms, including especially the myriad bacteria in the Earth’s soil. Margulis remembers that she kept asking,
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“Why does everybody agree that atmospheric oxygen . . . comes from life, but no one speaks about the other atmospheric gases coming from life?” 63 Soon several of her colleagues recommended that she speak to James Lovelock, which led to a long and fruitful collaboration that resulted in the full scientific Gaia hypothesis.
The scientific backgrounds and areas of expertise of James Lovelock and Lynn Margulis turned out to be a perfect match. Margulis had no problem answering Lovelock’s many questions about the biological origins of atmospheric gases, while Lovelock contributed concepts from chemistry, thermodynamics, and cybernetics to the emerging Gaia theory. Thus the two scientists were able gradually to identify a complex network of feedback loops that—so they hypothesized—bring about the self-regulation of the planetary system.
The outstanding feature of these feedback loops is that they link together living and nonliving systems. We can no longer think of rocks, animals, and plants as being separate. Gaia theory shows that there is a tight interlocking between the planet’s living parts—plants, microorganisms, and animals—and its nonliving parts—rocks, oceans, and the atmosphere.
The carbon dioxide cycle is a good illustration of this point. 64 The Earth’s volcanoes have spewed out huge amounts of carbon dioxide (C0 2 ) for millions of years. Since C0 2 is one of the main greenhouse gases, Gaia needs to pump it out of the atmosphere; otherwise it would get too hot for life. Plants and animals recycle massive amounts of C0 2 and oxygen in the processes of photosynthesis, respiration, and decay. However, these exchanges are always in balance and do not affect the level of C0 2 in the atmosphere. According to Gaia theory, the excess of carbon dioxide in the atmosphere is removed and recycled by a vast feedback loop, which involves rock weathering as a key ingredient.
In the process of rock weathering, rocks combine with rainwater and carbon dioxide to form various chemicals, called carbonates. The C0 2 is thus taken out of the atmosphere and bound in liquid solutions. These are purely chemical processes that do not require the participation of life. However, Lovelock and others discovered that the presence of soil bacteria vastly increases the
Figure 5-4
Oceanic alga (coccolithophore) with chalk shell.
rate of rock weathering. In a sense, these soil bacteria act as catalysts for the process of rock weathering, and the entire carbon dioxide cycle could be viewed as the biological equivalent of the catalytic cycles studied by Manfred Eigen.
The carbonates are then washed down into the ocean, where tiny algae, invisible to the naked eye, absorb them and use them to make exquisite shells of chalk (calcium carbonate). So the C0 2 that was in the atmosphere has now ended up in the shells of those minute algae (figure 5-4). In addition, ocean algae also absorb carbon dioxide directly from the air.
When the algae die, their shells rain down to the ocean floor, where they form massive sediments of limestone (another form of calcium carbonate). Because of their enormous weight, the limestone sediments gradually sink into the mantle of the Earth and melt and may even trigger the movements of tectonic plates. Eventually some of the C0 2 contained in the molten rocks is spewed out again by volcanoes and sent on another round in the great Gaian cycle.
The entire cycle—linking volcanoes to rock weathering, to soil bacteria, to oceanic algae, to limestone sediments, and back to volcanoes—acts as a giant feedback loop, which contributes to the regulation of the Earth’s temperature. As the sun gets hotter, bacterial action in the soil is stimulated, which increases the rate of
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rock weathering. This in turn pumps more C0 2 out of the atmo- sph ere and thus cools the planet. According to Lovelock and Mar- gulis, similar feedback cycles—interlinking plants and rocks, animals and atmospheric gases, microorganisms and the oceans— regulate the Earth’s climate, the salinity of its oceans, and other important planetary conditions.
Gaia theory looks at life in a systemic way, bringing together geology, microbiology, atmospheric chemistry, and other disciplines whose practitioners are not used to communicating with each other. Lovelock and Margulis challenged the conventional view that those are separate disciplines, that the forces of geology set the conditions for life on Earth and that the plants and animals were mere passengers who by chance found just the right conditions for their evolution. According to Gaia theory, life creates the conditions for its own existence. In the words of Lynn Margulis:
Simply stated, the [Gaia] hypothesis says that the surface of the Earth, which we’ve always considered to be the environment of life, is really part of life. The blanket of air—the troposphere—should be considered a circulatory system, produced and sustained by life.
. . . When scientists tell us that life adapts to an essentially passive environment of chemistry, physics, and rocks, they perpetuate a severely distorted view. Life actually makes and forms and changes the environment to which it adapts. Then that “environment” feeds back on the life that is changing and acting and growing in it. There are constant cyclical interactions. 65
At first the resistance of the scientific community to this new view of life was so strong that the authors found it impossible to publish their hypothesis. Established academic journals, such as Science and Nature, turned it down. Finally the astronomer Carl Sagan, who served as editor of the journal Icarus, invited Lovelock and Margulis to publish the Gaia hypothesis in his journal. 66 It is intriguing that of all the theories and models of self-organization, the Gaia hypothesis encountered by far the strongest resistance. One is tempted to wonder whether this highly irrational reaction by the scientific establishment was triggered by the evocation of Gaia, the powerful archetypal myth.
MODELS OF SELF-ORGANIZATION