Life as Geological Factor

The highest level of biological systems, biosphere, can be considered as a part of more global geological system. Geochemical processes gave rise to life; in its turn, life became an active participant of these processes.

Speaking about life as a geological factor, it is possible to put aside biological peculiarities of living systems and concentrate on geochemical characteristics of life and its influence on geological objects. 'Living matter', in accordance with the views of V. I. Vernadsky, is ''a totality of organisms, reduced to its weight, chemical composition and energy.'' At the geological level, life operates through these global parameters. From the biogeochemical point of view, the swarm of locusts is a moving dispersed rock, which is very active chemically.

Biosphere is a global form of living matter, a manifestation of its continuity. It consists of different, but closely connected forms of life. Biosphere is an ocean of genes; informative genes of higher organisms are a very small part of it. The reproductive part of living matter evolves its iterative self-reproduction; the somatic one supports its metabolism and growth. According to V. I. Vernadsky, biosphere tends to maximal intensity of biogenic migration of elements. It is close to Lotka's maximum power principle: the intensification of global biogeochemical cycling can be based only on increase of energetic power of biosphere.

The properties of living matter as a geochemical substance are the following:

• its chemical composition is stable only dynamically, while organisms are living;

• the chemical composition is very diverse (2 million organic substances in living objects as against 2000 minerals in animated nature);

• it has a huge free energy - exergy (similar to fresh lava, but much more durable);

• it is quite mobile: actively (because of active movement of such organisms as animals) and passively (as a result of reproduction and growth, the pressure of life: direct offspring of the gigantic puffball, producing 7.5 billion spores, can exceed the mass of the Earth by 800 times);

• it is dispersed matter, which consists of separate particles (living organisms) with the size from 20 nm to 100 m (the difference is in billion times).

The processes in living organisms, important for geological processes, are (1) formation of bodies; (2) excretion of products of metabolism; (3) transportation of indigested substances through the digestive tract; (4) movement; and (5) mechanical influence on environment.

The geochemical functions of living matter are energetic (photo- and chemosynthesis, energy transmission in food webs); transport (matter transportation against gravity and horizontally); extracting (involving matter from environment to the biogeochemical cycling); concentrating (selected accumulation of chemical substances in bodies or excrements); and environmental (influence on physical or chemical parameters of environment).

J.-B. Lamarck asserted already that practically all natural landscapes and the Earth's crust rocks are results of living matter functioning. V. I. Vernadsky added to this thesis the idea about life as an integral part of geological processes. Primary rocks, originated without participation of biosphere, are massive and homogenous; the existing diversity of rocks was created by life.

The Earth's crust consists of sediment rocks. The main stages of their formation are hypergenesis (destruction of parent materials, mainly as a result of living organisms' activity); sedimentogenesis (accumulation, under essential influence of biofiltrating organisms, of sediments in friable forms: clay, silt, peat); diagenesis (sediment compaction with participation of bacteria, mud-eaters, fossorial animals); and katagenesis (further compaction, sediment rocks transform to metamorphic ones).

The main biogenic sediment rocks are carbonate rocks (formed mainly by phytoplankton); siliceous rocks (sponges, radiolarians, diatoms); combustible organic substances (coal from peat, shale oil from sapropel, oil from plankton organic substances); and phosphate rocks (excrements, mass suffocations of marine organisms). Such minerals as bauxites, ferruginous and manganous rocks are formed as a result of activity of bacteria.

Under the sediment stratum, there is also biogenic matter, but melted in the course of the lithogenesis. From the ocean bottom, sediments deepen under continents, following the global Earth's crust movement.

Biosphere controls composition of the atmosphere; the content of oxygen and carbonic gas is a direct result of living matter activity. One can say the same about composition of ocean water. Life created such new components of environment as soil with hybrid (not pure biological, not pure abiotic) nature. It influences even such an ener-gywise important global parameter as the reflectivity factor of different parts of the Earth's surface.

Geography of Life

Distribution of life within the Earth is limited by some physical and chemical parameters. In some conditions, living organisms can realize all their functions; in some others, their functionality is not full (usually the most sensitive process is reproduction). The first part of biosphere can be called a 'field of life'; the second one is a 'field of survival', or 'parabiosphere' in terminology of J. Hutchinson (1884-1972).

A very important parameter is temperature: too high one leads to protein degradation, too low temperature prevents activity of enzymes. Water is necessary in liquid form.

Some 'psychrophilic' (cold-loving) forms of bacteria, algae, and fungi can live and reproduce under c. -7 °C; the rootage of such higher plants as the Kamchatka rhododendron operates under 0 °C. At the same time, there are 'thermophilic' (heat-loving) species of eels, worms, and insects which live in thermal springs (50-80 °C). Spores of bacteria can survive in a temperature of 160-180 °C. Life has filled territories with all thermal conditions: from the Antarctic (the summer air temperature is 0 ° C, the winter one is -40 °C) to the most inclement deserts (45 °C in summer, 0 °C in winter).

One of the factors determining the upper board of terrestrial life is the atmospheric pressure and availability of oxygen and carbonic gas. At a height of 6200 m, a partial pressure ofcarbonic gas is 2 times less than normal one, and plants cannot grow. The upper board of ecosystems of Alpine belt is at the height of 2000-3500 m; in the Pamir mountains, it is 4800 m. In eternal ice at the height of 6000 m, one can find snow fleas and flightless grasshoppers.

The near-surface Earth stratum can be inhabited at a depth of 1-3 km. Although if groundwater is too salted (more than 270gl_1, that is, 10 times more than in the seawater) or its reservoir is isolated, life can be lacking even at a depth of 0.5 km.

The main limiting factors in the oceans are the deficiency of mineral nutrition for plants and the impossibility of photosynthesis in ocean depths. Sometimes, a chemical contamination can take place (e.g., the Black Sea is polluted by hydrogen sulfide). High pressure is not so essential; under 1000 atm at the depth of 10 km, there are several hundred species. Sediments on the sea bottom can be inhabited at the depth of 120 m.

Atmosphere is, generally speaking, only a field of survival. Flying insects and birds can spend a lot oftime in the air, but some part of their life is obviously connected with the land. Condor can be observed at the height of 7 km; viable bacteria were found at the height of 77 km.

Thus, the field of life in the ocean is water stratum and bottom sediments of quite various thicknesses. In the continents, it is thin ground and thick underground layers.

The vertical films of life are the following: surface (plankton) and bottom (benthos) in sea, and surface and soil in land. The horizontal concentrations are littoral, reef, sargasso, upwelling, abyssal rift (marine); coastal, riverside, tropic forest, lake (terrestrial). Some of them are represented in Figure 2.

Abyssal rift concentrations of life are based on chemo-trophic producers and do not depend on the solar radiation. They can be considered as a reserve of biosphere in case of some global cataclysm, and, according to one hypothesis, are an initial form of living matter. It is also an illustration of the possibility of life existing without entry of solar radiation (e.g., under ice in the big planets of the solar system).

History of Life

Life is a process, and it is not only self-reproduction, but also permanent development, increase of complexity and organizational levels. This process is not smooth and linear; it is a chain of alternate rapid changes and periods of stability. The history of life is characterized by several great revolutions, and the first ofthem is the transition from chemical reactions to biochemical ones. Understanding of life origin is, besides other aspects, the best way to obtain an appropriate definition of life.

Figure 2 The vertical films of life (I, surface (plankton); II, bottom (benthos)) and horizontal concentrations (1, littoral; 2, sargasso; 3, reef; 4, upwelling, 5, abyssal rift; 6, coastal) in marine and neighboring ecosystems.

Origin of Life

From ancient time it was recognized that self-generation of living organisms (usually from rotting organic substances) can take place. Such thinkers and scientists as Aristotle, F. Bacon, R. Descartes, and G. Galilee shared this opinion. Correspondingly, the problem of initial origin of life was irrelevant. Only in 1688 F. Redi (1626-98) experimentally demonstrated that maggots appear in carrion meat only in the condition of access of flies. The statement ''all living beings originate from living beings'' is called the principle of Redi.

Another view, incompatible with the idea of initial self-origin of life, is the opinion about the impossibility of synthesis of organic substances, which contain a special living force - vis vitalis. However, in 1828, F. Wohler (1800-82) synthesized carbamide from ammonium cyanide. During the nineteenth century, c. 75 000 different organic substances from inorganic ones were synthesized (and a billion of them are received now).

The first theories concerning origin of life were proposed by E. F. W. Pfluger (1829-1910), H. F. Osborn (1857-1935), and others. The theories about genesis of organic matter proposed by A. I. Oparin (1924) and J. B. S. Haldane (1929) are still of great interest.

Self-organization took place from the very beginning of the formation of the world. Other prerequisites of the life origin were formation of planetary systems at the macrolevel and heavy elements at the microlevel. A perspective planet must have circular orbit and mass, which is similar to the Earth's (its atmosphere can lose hydrogen, but not carbonic gas and oxygen). A central star must have stable radiation.

One of the important prerequisites of the origin of life was synthesis of simple organic molecules in space. Such substances as ammonia, cyanhydric acid, methyl acetylene, and others are widespread in interstellar space; formaldehyde forms even clouds with concentration of 1000 molecules per cubic centimeter. The Earth gained organics during its formation and is still obtaining it through meteorites.

The initial atmosphere consisted mainly of hydrogen, helium, and methane. The anoxic conditions allowed synthesis of simple organic substances, similar to the ones originated in space. A very important point was the transition of water to liquid state. In water, much more complex organic molecules can be generated. As was shown by experiments of S. L. Miller, electric discharge in mixture of methane, ammonia, hydrogen, and water can produce a number of complex organic molecules, for example, amino acids. During 2 weeks, 15% of methane transformed to organics. All 20 amino acids, forming proteins, can be obtained inorganically, as well as nucleo-tides, fats, sugars, etc.

Organic substances are so multifarious by their functional properties that the selection of proper elements for the formation of biochemical systems was not so difficult (but could be random). Probability of life origin was quite high, although there were, probably, bottlenecks in the formation of some important reactions.

The second prerequisite of life was the availability of external energy sources. During first stages of the life formation, it was, probably, ultraviolet solar radiation. In accordance with the data of K. Sagan, 2400-2900 A wavelength radiation can evolve 1% solution of organic substances in ocean water, failing the ozone shield. Corresponding energy is sufficient for existence of stable populations of bacteria. Molecules of ATP can operate in this case as primitive chemical accumulators of the solar energy. This substance may have played a similar role in the course of the origin of life.

The third important prerequisite of the origin of life is the abiotic water cycling. Dynamic equilibrium of life in the planetary scale can be reached only with the help of such global intermixing machine. Cosmic factors (territorial and temporal irregularity of heating by a central star, tidal influence of neighboring celestial bodies, etc.) determining the cycling are widespread in space.

Life originated as a biological cycling, united biochemical synthesis, and destruction in one process. According to K. Bernard, life is always a combination of these two tendencies. From the very beginning, reactions of primordial photosynthesis (initial producing) were accompanied by reactions using the energy of synthesized substances for new synthesis and, finally, for their destruction and return of elementary substances to environment (initial consuming). In the course of the corpusclezation process, these two groups of reactions begot first producers and reducers. Life as a unity of synthesis and destruction was not based at first on separate organisms. According to the statement of J. D. Bernal (1969), life appeared earlier than living organisms.

However, very often life is defined at the cellular level. Really, compartmentalization of groups of connected chemical reactions can evolve much more effective and ordered realization of the living-like processes, and origin of cell produced a revolution of life functioning. Theories of the origin of life attempt to explain a mechanism of formation of a primordial single cell from which all modern life originates.

Experiments have shown that formation of cell-like objects is quite usual for organic blends. First candidates for the role of initial cells are 'coacervates', discovered by G. H. Bunoenberg de Yong (1949). They are separated from the blend by a surface lipid film and can selectively absorb different substances from environment. The absorption can lead to dividing a drop into two similar parts.

S. Fox in 1970 found another potential pre-cell, 'microsphere'. Its properties are similar to coacervate ones, but it has a fixed size (about 10"6 m), is quite stable, and does not tend to merge with other microspheres. Its lipid membrane is bilayer. G. Tibor (1980) has considered microspheres (containing reagents of special autocatalytic reactions) as the first form of life and called them 'chemotones'.

The 'autocatalytic' origin of life is now universally recognized. It is not evident, what type of autocatalytic reaction was initial; now the general cellular autocatalytic process is very complex and includes many intermediate steps. The main players of this process are nucleic acids and proteins; its very simplified scheme is represented in Figure 3. Nucleic acids can store information and replicate, but need catalysts for this; proteins are good catalysts, but cannot replicate. Two groups of proteins catalyze self-reproduction of DNA (polymerases) and synthesis on the DNA matrix of both protein groups (synthetases).

Figure 3 Simplest scheme of autocatalytic reproduction of cells.

There are two main hypotheses about the formation of the autocatalytic loop. The first one was deeply elaborated by M. Eigen and his co-authors in 1979 in the model of'hypercycle'. It is based on the assumption about initial origin of many-component autocatalysis, including at least two components: RNA and a protein. The second theory, developed by G. F.Joyce in 1989, presupposes a simpler self-catalysis of RNA. In both approaches, RNA is considered as natural predecessor of DNA.

Thus, the origin of pre-cell consists in compart-mentalization in separate volumes, bounded by lipid membranes, reagents of reactions, aimed at realization of at least two key functions: assimilation of energy and self-replication, leading to dividing the cell into two. Origin of the hereditary code and cell reproduction launch the process of Darwinian selection.

Modern science has explained many peculiarities of life development, but it is still impossible to check corresponding hypotheses practically. It is supposed, that some events should happen accidentally; even in laboratory, occurrence of a propitious condition can take thousand years, whereas in nature a million years. Anyway, it now does not look so plausible that life has an extraterrestrial origin, as it was supposed by W. Thomson (1871), G. L. F. Helmholtz (1872), S. A. Arrhenius (1915), and many others. Space still sends to the Earth organic substance -material for life - but nobody finds organisms in meteorites. All earthly organisms are very closely connected; it is not so evident that a single organism can give rise to life in a planet (not only one-time explosion) even in case of proper conditions.

Main Stages of the Life Evolution

Several decades ago, it was recognized that the age of life is c. 1 billion years. But last discoveries in Africa have shown that as long as 3.2 billion years ago there were bacteria-like forms of life. It is possible, reasoning from isotopic composition of oldest carbonates from Greenland, that life reached the cell level 3.9 billion years ago. The Earth's age is c. 4.6 billion years; if one excludes the first stage of intensive meteorite bombing (about 0.5 billion years), the way from simple organic molecules to life lasted only a few million years.

Probably, the first type of chemosynthesis was synthesis of methane from carbonic acid and hydrogen by organisms, similar to present-day methane bacteria. Under the influence of ultraviolet radiation, methane transformed to organic substances, consumed by other organisms, which returned carbonic acid to water. It was the first biological cycling; it came to naught in the course of decrease of hydrogen in atmosphere.

Concurrently, first forms of photosynthesis were originated. Oldest discovered organisms (c. 3.5 billion years old) are similar to cyanobacteria, that is, they were phototrophs. First phototrophic organisms did not produce oxygen, but 2.5 billion years ago the photosynthesis on the basis of chlorophyll arose. It was the start of the oxygen revolution, which led 0.5 billion years later to the total reorganization of biosphere. After some regression, explained by toxicity of oxygen for oldest organisms, life formed a new mechanism of oxygen use - respiration.

The oxygen revolution, probably, stimulated the further great step - origin of eukaryotic unicellular organisms 1.9-2 billion years ago. It was huge progress in structural and functional organization of cells; special organs (organelles) for different functions (inheritance, photosynthesis, respiration, etc.) arose, mainly as a result of symbiotic incorporation of other prokaryotic cells.

A little later, the next revolution took place: the first multicellular organisms originated about 1.8 billion years ago. The path to multicellular forms led through colonies of unicellular organisms, which are typical for many groups: flagellates, infusorians, algae, etc. Cells gradually differentiated for reproducing, alimentary, impellent, etc., purposes. Transition to multicellularity took place independently in different groups of unicellular organisms. By the beginning of Cambrian period, all kingdoms and subkingdoms, excluding higher plants, had existed, although practically only the zone of continental shelf was inhabited.

A very important point of the life history is the border between Cryptozoic and Phanerozoic eons. Many different groups of animals (sponges, arthropoda, echinodermata, mollusks, etc.) acquired exoskeleton. It is explained by the growth of oxygen concentration in the atmosphere that facilitated synthesis of collagen. Life explosion in Cambrian period is an explosion of extant fossils.

Approximately at the same time the inhabiting of lands started. As usual, new niche development provoked intensive process of new form building. The last big group - higher plans - originated and began its intensive evolution. Landscapes became more similar to modern ones: after origin of first forests in later Devonian period, they started to regulate surface-water flows, and rivers and lakes obtained the modern form.

Geochronology of the evolution of life is represented in Table 4 and Figure 4. Last thousand years is nothing in the geological scale, but they are accompanied by the extremely quick development of principally a new global factor - the human mind.

Human Mind as a Stage of the Life Evolution

There are two main positions concerning the problem of the human mind origin; it is considered as a result of either gradual development of animal abilities or drastic change of nervous system's functioning. For example, C. Darwin considered the difference between thinking of human and that of animals as not qualitative, but only quantitative. At the same time, followers of the behavior-istic theory proclaim that there is a gulf between people and animals. As usual, the truth is somewhere in between. On the one hand, we cannot consider intelligence as an immanent property of life. Its development is characterized by evident leaps, the most essential of which was the origin of the human mind. On the other hand, most of the intellectual abilities of people can be observed in behavior of higher animals. Experiments on fosterage of chimpanzee babies in human families, which were started in 1913, have shown that their intellect can reach the level of a 2.5-year-old child.

Intellect is an ability to make decision in the situations where reflexive decisions are underspecified. It is a process of logic operation with some abstract symbols, expressing knowledge of the individual (or, in other words, use of a model of the world, formed in his mind). It is interesting that intellectual abilities of animals and birds formed similarly, but independently and on a different morphological basis: for example, birds have no cerebral cortex.

Besides all the evolutionary innovations, mind gives to a species some advantages in competition with other ones. The human mind proved to be so effective that it spared mankind from competition with other species. The human population is out from the ecosystem regulation, and there can be danger for its future.

Possibilities of intellectual development appeared after the origin ofnervous system (as long ago as Cryptozoic eon). A network of specialized commutation cells ('neurons') is a reflection in the living organism morphology of the information constituent of the world. It gives possibility to collect, transmit, process, and store information. The human nervous system consists of about 1010 neurons, and each of them has thousands of 'synapses', connecting it with other neurons. All of them together form a 'neural network', which is well-known in informatics as a universal basis of self-organizing information-processing systems. At the same time, abstract mathematical neural networks are insufficient for understanding of a real nervous system and its center, the brain, because the latter has a very special, evolutionarily determined structure.

Increasingly complex algorithms ofinformation processing led to both morphological progress and improvement

Table 4 Geochronology of life evolution

Eon

Era

Period

Beginning and end, million years

o

Archean

45002600

Origin of life (more than 3.5 billions years ago). Primordial anoxic organisms. Appearance of prokaryotes

O

Proterozoic

Lower Proterozoe

26001600

Primitive unicellular photosynthetic and nitrofixing organisms

Riphey

1600-570

Appearance of eukaryotes. Origin of multicellular organisms. Wide expansion of bacteria, fungi, and algae

Cambrian

570-500

Appearance and expansion of marine invertebrates

Ordovician

500-440

Origin and expansion of lower terrestrial plants. Appearance of terrestrial invertebrates

Paleozoic

Silurian

440-410

Maximal development of marine invertebrates

Devonian

410-350

Origin of terrestrial vascular plants. Appearance of insects, first vertebral animals

Carbonic

350-285

Maximal development of gigantic mosses and horsetails. Development of amphibians. Formation of coal as a result of disposal of plant residues

ic oi

ro

Permian

285-230

Origin of gymnospermous plants, extinction of pteridophytes. Appearance of big reptiles

er n

h

Triassic

230-195

Development of gymnospermous plants. Expansion of big reptiles

CL

ic oi z o rn e

Jurassic

195-137

Further development of gymnospermous plants. Origin of immediate ancestors of birds

Cretaceous

137-67

Origin of angiosperm plants. Extinction of big reptiles. Disposal of carbon in the form of chalk (calcium carbonate)

ic

Paleogene

67-25

Wide spreading of angiosperm plants. Intensive development of birds and mammals

O

Neogene

25-1.5

Formation of modern flora and fauna. Origin and development of primordial anthropoids

Quaternary

1.5-0

Origin of Homo sapiens. Development of the human society

of using abstract languages for information coding. The human language, developed in the last millennia, has given a principally new possibility to transmit a huge amount of information between generations passing over genome. It has incredibly accelerated the evolution, and created new ways of its realization. Having an image of the world in his mind, man can influence his own evolution.

As an information system, the nervous system superseded the older chemical one - the hormonal system. It does not replace the latter system completely, but it became a superstructure on its basis. Usually the two systems function consistently, but sometimes they can give different recommendations; in this case, one can say that there is a contradiction between one's mind and feelings.

The multilayer character of the human information system is one of the aspects of a vital issue about scientific explanation of the phenomenon of consciousness. The mind-body problem is still unsettled; it is one of the last secrets of the universe. There are no serious ideas, in both natural science and philosophy, about a general approach to the problem investigation.

Computer science has given a brilliant possibility to model information processes; it is quite imaginable to make a robot, realizing all the functions of man, including his intellectual abilities. But can we secure a feeling of pain for this robot, or give him self-consciousness? Can artificial intellectual devices develop their mind, at least after long-term evolution? This matter is beyond the fields of both electronics and cybernetics. Probably, the nature of the human mind is bipartite and has equally important cybernetic and chemical components. But the way of their synergy in the human body is still inscrutable.

Period Age

Quaternary o

Tertiary O

Cretaceous

Jurassic

Triassic

Permian

Carbonic

Devonian

Silurian

Ordovician

Cambrian

Sponges

Protozoa

Sponges

Protozoa

Figure 4 Diagram of animal evolution.

Perspectives of Life

The philosophical problem of life is a problem of origin and being of man; it is another understanding of life, not as a biological phenomenon. However, these two approaches supplement each other: on the one hand, man is a biological being; on the other hand, science sees the world through human eyes, and it is necessary to take into considerations the peculiarities of the measuring instrument. The origin of consciousness is a principally new stage of life evolution, and the future of life depends now on tendencies of the human evolution.

According to F. Engels' (1820-95), in man the nature comes to self-understanding. N. F. Fedorov (1828-1903) developed this idea and said that it also found in man a new mechanism to self-control. As life integrated

Period Age

Quaternary o

Tertiary O

Cretaceous

Jurassic

Triassic

Permian

Carbonic

Devonian

Silurian

Ordovician

Cambrian formerly geological processes, the human society is integrating life into its functions. Biosphere becomes a part of a larger system - 'noosphere'.

The term noosphere (from Greek word noos - mind) was proposed by E. Le Roy (1870-1954) and then essentially developed by other scientists. According to V. I. Vernadsy, noosphere is the next stage of biosphere, includes mankind and products of its activity, and is controlled by it to an essential degree. At present, mankind is not a good manager; there are a lot of ecological problems produced by human activity. Attention of people is focused mainly on technosphere, artificial product of human mind parasitized on biosphere. Perspectives of life depend on the success of people to find optimal ways of cooperation with nature and, particularly, include technosphere to the o

CO CD

natural global cycling. Human influence is now much more essential for the destiny of life, than potentially dangerous geological (S. A. Arrhenius) or cosmic (S. Hocking) factors.

Summary

Natural evolution of Earth life has formed biological systems at different levels: biochemical, cellular, organism, ecosystem. Science has collected a lot of data about biological processes, but the process of their synthesis is only at its beginning.

Life is a global planetary process and involves in its functions all its forms of life. It intensively transforms its environment on all the levels: from biochemical processes in a single cell up to the global biogeochemical cycling on the scale of the Earth. Biosphere with its potential can help mankind solve many of its problems, but at the moment they are still in contradiction.

Understanding of life presupposes a knowledge concerning its history and laws of its evolution. The latest discoveries have made the process of the life origin more understandable, but further evolution of life is still unclear. Anthropogenic global change in combination with natural tendencies can give unexpected results. Further existence of life now depends on the ability of people to analyze the current situation and make right decisions.

See also-. Biodiversity; Biosphere: Vernadsky's Concept; Gaia Hypothesis; Macroevolution; Noosphere; Phenomenon of Life: General Aspects; Succession.

Further Reading

Calder WA (1984) Size, Function and Life History. Cambridge, MA:

Harvard University Press. Forman RTT and Gordon M (1986) Landscape Ecology. New York: Wiley.

Hutchinson GE (1965) The Ecological Theater and the Evolutionary Play.

New Haven, CT: Yale University Press. Jablonka E and Lamb MJ (2005) Evolution in Four Dimensions. Genetic, Epigenetic, Behavioral and Symbolic Variation in the History of Life. Cambridge, MA: MIT Press. Jorgensen SE (1992) Integration of Ecosystem Theories: A Pattern.

Dordrecht: Kluwer. Kareiva PM, Kingsolver JG, and Huey RB (eds.) (1993) Biotic Interactions and Global Change. Sunderland, MA: Sinauer. Lehninger A (1982) Principles of Biogeochemistry. London: Worth Publishers.

Lovelock JE (1989) Geophysiology, the science of Gaia. Reviews of

Geophysics 27: 215-222. Margulis L and Sagan D (1986) Microcosmos: Four Billion Years of

Microbial Evolution. New York: Simon & Schuster. Marler PR and Hamilton WJ (1966) Mechanisms of Animal Behavior.

New York: Wiley. Maynard Smith J (1982) Evolution and the Theory of Games.

Cambridge: Cambridge University Press. Odum HT (1971) Environment, Power, and Society. New York: Wiley. Oparin AI (1957) The Origin of Life on Earth. New York: Academic Press. Partidge L and Harvey PH (1988) The ecological context of life history evolution. Science 241: 1449-1455. Pert CB (1999) Molecules of Emotion. New York: Touchstone. Pianka ER (1994) Evolutionary Ecology. New York: Harper Collins. Pickett STA, Kolasa J, and Jones CG (1994) Ecological Understanding: The Nature of Theory and the Theory of Nature. San Diego, CA: Academic Press. Schneider SH and Boston PJ (eds.) (1991) Scientists on Gaia.

Cambridge, MA: MIT Press. Watson JD and Berry A (2003) DNA: The Secret of Life. New York:

Random House. Wilson EO (1992) The Diversity of Life. New York: Norton.

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