Gaia Hypothesis

P.J. Boston , in Encyclopedia of Ecology, 2008

Introduction

The Gaia hypothesis, named after the ancient Greek goddess of Globe, posits that Earth and its biological systems behave every bit a huge unmarried entity. This entity has closely controlled self-regulatory negative feedback loops that proceed the conditions on the planet within boundaries that are favorable to life. Introduced in the early 1970s, the idea was conceived past chemist and inventor James E. Lovelock and biologist Lynn Margulis. This new mode of looking at global ecology and evolution differs from the classical picture of environmental as a biological response to a carte du jour of physical conditions. The thought of co-evolution of biology and the physical environment where each influences the other was suggested as early as the mid-1700s, only never every bit strongly as Gaia, which claims the power of biology to control the nonliving environment. More than recently, the terms Gaian science or Gaian theory have go more common than the original Gaia hypothesis because of modifications in response to criticisms and expansion of our scientific understanding.

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GAIA HYPOTHESIS

T. Lenton , in Encyclopedia of Atmospheric Sciences, 2003

Introduction

The Gaia hypothesis postulates that the Earth's surface is maintained in a habitable state by self-regulating feedback mechanisms involving organisms tightly coupled to their surroundings. The concept is based on several observations:

•

The atmosphere is in an farthermost state of thermodynamic disequilibrium owing to the activities of life, nevertheless aspects of its limerick are remarkably stable.

•

Present weather at the surface of the World are close to optimal for the dominant organisms.

•

Life has persisted for over iii.eight billion years despite increasing solar luminosity and variable exchange of matter with the inner Earth.

•

The Earth organization has repeatedly recovered from massive perturbations.

The Daisyworld model demonstrated that planetary self-regulation tin occur without teleology, in a style consequent with natural selection. Since the origin of life, organisms accept had a profound effect on the World's atmospheric limerick and the climate. The 'faint immature Sun' was initially counteracted past a carbon dioxide and methane 'greenhouse' atmosphere. The biological amplification of silicate rock weathering has progressively reduced the carbon dioxide content of the atmosphere and acted as a long-term climate stabilizer. Atmospheric oxygen rose in a stepwise way to ∼21% of the atmosphere, virtually which information technology has been tightly regulated for the by 350   million years. Feedbacks involving terrestrial and marine biota as well affect the climate over shorter time scales. The predominance of positive feedback in the recent glacial–interglacial cycles suggests that the Globe arrangement is nearing a transition to an culling land. Eventually, self-regulation volition collapse and the Globe will be sterilized, but this is unlikely to occur for at least another 0.v–1.two billion years.

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Mycorrhizal Fungi☆

L.Thousand. Egerton-Warburton , ... S.Fifty. Finkelman , in Reference Module in World Systems and Ecology Sciences, 2013

Summary

Lovelock's Gaia hypothesis conceptualized biodiversity and mutualism in their most advanced and elegant integration. In mycorrhizae, diversity and mutualistic functioning unite successive systems into networks and complex systems. In guild to show that complexity has increased overall, it is sufficient to evidence, that – all other things being equal – connections have increased in at least one dimension. What is defective is the power to make predictions about how complexity in mycorrhizal communities will alter their function as the systems and/or their surroundings is contradistinct past human impacts and global change. Combining metagenomics, transcriptomics, molecular, metabolic, and biochemical data with nonlinear mathematical models might provide the foundations and rules for understanding mycorrhizal complication. The limitations and utility of any data, notwithstanding, remain in developing data-mining and complexity-modeling tools and techniques to utilize effectively the data from a local and global perspective, because data are gathered on scales from molecules to genomes, organelles, cells, tissues, and organs. Bioinformatics is the acquisition of cognition by means of computational tools for the organisation, management, and mining of genetic biological data. These belittling tools are being increasingly applied to the oceans of data collected by metagenomics studies. A more appropriate term for mycorrhizal systems may exist 'ecoinformatics' or the accumulation of ecologically based data sets appropriate to mycorrhizae in situ, followed by data integration. In doing then, it will then be appropriate to say that diversity and mutualism provide ecosystem function and what that performance may exist.

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The physical and chemical bases of energy

David E. Reichle , in The Global Carbon Bicycle and Climate Alter, 2020

2.four Gaia hypothesis

The Gaia Hypothesis proposed by James Lovelock (1972) suggests that living organisms on the planet interact with their surrounding inorganic surround to form a synergetic and self-regulating system that created, and now maintains, the climate and biochemical conditions that make life on Earth possible. Gaia bases this postulate on the fact that the biosphere, and the evolution or organisms, affects the stability of global temperature, salinity of seawater, and other environmental variables. For instance, fifty-fifty though the luminosity of the dominicus, the Earth's heat source, has increased about 30% since life began almost 4 billion years ago, the living system has reacted as a whole to maintain temperatures at a level suitable for life. Cloud formation over the open bounding main is nearly entirely a function of oceanic algae that emit sulfur molecules as waste product metabolites which get condensation nuclei for pelting. Clouds, in plow, assist regulate surface temperatures.

Lovelock compared the atmospheres of Mars and Globe, and noted that the Earth'due south high levels of oxygen and nitrogen were abnormal and thermodynamically in disequilibrium. The 21% oxygen content of the atmosphere is an obvious outcome of living organisms, and the levels of other gases, NH3 and CH4, are higher than would be expected for an oxygen-rich atmosphere. Biological activity also explains why the atmosphere is not mainly CO2 and why the oceans are not more saline. Gaia postulates that atmospheric condition on Earth are then unusual that they could merely effect from the activeness of the biosphere (Lovelock and Margulis, 1974).

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Futurity Climate

Martin Rice , Ann Henderson-Sellers , in The Future of the World'due south Climate (Second Edition), 2012

18.i.2 The Gaia Hypothesis

The Gaia hypothesis (Lovelock, 1972; Lovelock and Margulis, 1973) postulates: "the climate and chemical composition of the Earth's surface environment is, and has been, regulated in a state tolerable for the biota" (Lovelock, 1989, p. 215). The Gaia hypothesis ( Figure xviii.one) – named later on the Greek goddess of Earth by the author William Golding (Lovelock, 2009) – was criticized for not fully factoring in evolution by natural selection and, in detail, competition between organisms (due east.g., Dawkins, 1982). In response, Lovelock contended that, "In no way is this [Gaia] theory a contradiction of Darwin'due south corking vision. It is an extension to it to include the largest living organism in the Solar System, the Earth itself" (Lovelock, 1986, p. 25). The Daisyworld model (Figure 18.2) (Lovelock, 1983; Watson and Lovelock, 1983) was developed to illustrate how Gaia may work (Kump and Lovelock, 1995). It also provides an initial 'mathematical framework' for understanding cocky-regulation (Lenton, 1998).

Figure 18.2. Daisyworld and Woollyworld are both extremely simplified depictions of planetary systems: the erstwhile due to Lovelock (1979) and the latter described in outline by Schellnhuber (1999). On Daisyworld there are simply ii life forms: white and black daisies. (a) Fraction of planet Daisyworld covered by dissimilar daisies as solar luminosity increases over time; (b) how the global mean planetary temperature on Daisyworld is 'controlled' by the daisies; (c) schematic of some of the inhabitants of Woollyworld: populated by sheep that graze, reverberate solar radiation, and emit the greenhouse gas marsh gas (CH4).

 (Source: Parts (a) and (b) after McGuffie and Henderson-Sellers, 2005.)

Daisyworld is an imaginary planet, similar in many respects to Earth, on which grow only daisies. The daisies have an abundance of nutrients and water. Their ability to spread across the planetary surface depends only on temperature, and the relationship is parabolic, with minimum, optimum, and maximum temperatures for growth. The climate system is correspondingly simple. There are no clouds, and no greenhouse gases [GHGs]. The planetary energy balance is a function only of solar insolation, albedo and surface temperature, and planetary albedo depends on the areal coverage of the soil (which is grey) by black and white daisies.

(Kump and Lovelock, 1995, p. 539)

(Reprinted from Kump and Lovelock, 1995; with permission from Elsevier.)

The Gaia hypothesis has evolved over time, generating further research to test its robustness and accelerate the notion of a holistic ES. For example, "When introduced, this [Gaia] hypothesis was contrary to conventional wisdom that life adjusted to planetary conditions as it and they evolved in their dissever ways. We at present know that the hypothesis every bit originally stated was wrong because it is not life solitary but the whole ES that does the regulating" (Lovelock, 2009, p. 166). In a paper presented at the Un Academy in Tokyo on 25 September 1992, Lovelock explained that, although contentious, the Gaia hypothesis has generated many experiments (Lovelock, 1993). This department describes how – through these experiments – researchers have attempted to elucidate how the ES works past using climate as an illustrative example of how processes and feedbacks can operate homeostasis. Indicative of this thinking is the investigation of the role of algae in the body of water and its control of Globe's climate through the dimethyl sulfide (DMS) procedure.

18.i.2.1 Dimethyl Sulfide (DMS) and Climate Regulation

DMS, primal to numerous atmospheric processes, plays an important role in climate regulation (Kump and Lovelock, 1995; Ayers and Gillett, 2000). How an understanding of DMS was attained illustrates the evolution of integrated ESs thinking. For example, Ayers and Gillett (2000) explain that, despite the endeavor of a pocket-sized group of researchers (due east.grand., Junge and Manson, 1961; Fletcher, 1962), initial sulfur studies were limited. This was particularly considering the source of aerosol sulfur in regions far removed from volcanoes or anthropogenic emissions of sulfur dioxide had all the same to be determined, making it problematical to balance global sulfur budgets. The solution came "with the suggestion past Lovelock et al. (1972) that DMS was the 'missing' biogenic source of sulfur needed to remainder the global atmospheric sulfur budget" (Ayers and Gillett, 2000, p. 276).

Recognition of the importance of DMS, combined with before cloud microphysical studies (e.thou., Twomey, 1977; Twomey et al., 1984) that made the connection between droplet numbers and cloud radiative transfer properties (Ayers and Gillett, 2000), led to the Claw 1 hypothesis (Charlson et al., 1987). This hypothesis postulates, "biological regulation of the climate is possible through the effects of temperature and sunlight on phytoplankton population and dimethyl sulfide production" (Charlson et al., 1987, p. 665). In other words, DMS emissions from the oceans are influenced past climate and climate (through the impact of cloud albedo on the radiation budget) is affected by Cloud Condensation Nuclei (CCN) emanating from DMS emissions, "making climate and DMS emissions interdependent and closing a feedback loop" (Ayers and Gillett, 2000, p. 276).

Looking at the elucidation of DMS as part of the whole planet's chemistry and its importance to climate regulation, it seems that the systems arroyo advocated by Lovelock and others was an important framework. For example, Lenton (1998) argues that the Gaia hypothesis was used to make predictions, such equally "marine organisms would make volatile compounds that can transfer essential elements from the ocean to the land. The discovery that dimethyl sulfide and methyl iodide are the major atmospheric carriers of the sulfur and iodine cycles, respectively, support this proposition." (Lenton, 1998, p. 440). Another early case of ES framing using climate as an illustrator is seen in research on vegetation and climate interactions.

18.1.2.2 Vegetation and Climate Interactions

When large changes were recognized equally occurring in tropical rainforests (due east.one thousand., Salati and Vose, 1984), tests were conducted to try to determine their climatic touch (due east.chiliad., Henderson-Sellers and Gornitz, 1984). Fundamental aspects of this inquiry included the utilise of stable h2o isotopes to track hydrological changes (e.g., Salati et al., 1979; McGuffie and Henderson-Sellers, 2004) and model simulations of tropical deforestation that helped elucidate the importance of an accurate representation of vegetation in global climate modelling (e.one thousand., Dickinson and Henderson-Sellers, 1988; Henderson-Sellers et al., 2008).

Tropical deforestation simulations indicated a "sensitivity of the local climate to the removal of tropical forest…. Moreover, the scale of wet convergence changes, and possibly also cloud and convection changes, is such that there is a possibility that nonlocal climatic impacts may as well occur" (Zhang et al., 1996, p. 1516). Further studies (e.g., Zhang et al., 2001) found that tropical deforestation can touch large-scale atmospheric circulation. This supported previous Global Climate Model (GCM) studies (e.1000., Sud et al., 1988) and suggested that land-use change (eastward.g., tropical deforestation) may impact projections of futurity climate (cf. Pitman and de Noblet-Ducoudré, 2012, this volume). Notwithstanding, research in Amazonia had still to be studied in an interdisciplinary fashion (Dickinson, 1987), a central tenet of an ESs arroyo.

Although it was not clear how deforestation might threaten interdependent (homeostatic) systems considering "our scientific framework is yet inadequate to make such judgments" (Dickinson, 1987, p. 1), and well before detailed disciplinary research of the 1990s–2000s, inquiry scientists joined an international conference on 'Climatic, Biotic, and Man Interactions in the Humid Tropics with Emphasis on the Vegetation and Climatic Interactions in Amazonia' in Brazil in 1985. This meeting brought together some of the earth's top scientists to examine critical processes linking climate and vegetation in the tropics. The boiling tropics were called equally the focus because they were deemed of fundamental importance to the global climate. The urgent demand to carefully analyse land-use alter and climate in the humid torrid zone was combined with a want to communicate enquiry findings clearly (Figure xviii.3).

FIGURE 18.three. Woods moisture recycling increases precipitation in the Amazon, that is, why removing trees reduces rainfall. A Cathy Wilcox cartoon (first published on iv March 2005 on the front page of The Sydney Morning Herald, Australia) illustrating a geophysiological discovery made by tracking and modelling stable water isotopes.

 (Source: Reproduced by permission of Cathy Wilcox, SMH.)

Tropical forests are vulnerable to anthropogenic climate change through disturbances in precipitation and temperature (e.g., Lewis et al., 2011) and the compounding effects of tropical deforestation and greenhouse warming on climate have been investigated for some time (e.g., Zhang et al., 2001; Fearnside, 2011). There are many synergies operating among local people's survival, climate, vegetation, and land-utilize alter in the humid torrid zone. For case, every bit Fearnside (2011) notes, "Because one-half of the dry weight of the trees in a tropical forest is carbon, either deforestation or woods die-off releases this carbon in the grade of greenhouse gases such as carbon dioxide (COii) and methane (CH4), whether the trees are burned or simply left to rot" (Fearnside, 2011, p. 1283).

Gradually, every bit tropical forests became a key part of climate alter research and policy debate, simulations became more than like 'Gaian-blazon experiments' in which researchers attempted to describe how the ES works by using disturbances to the tropical forests' climate as an exemplar (e.g., Henderson-Sellers et al., 1988). An integrated systems approach (big picture perspective) evolved through the lens of ESS. This understanding prompted the concept of teleconnections and tipping points resulting from tropical deforestation in Amazonia, Africa, and South Eastern asia, every bit discussed past Lenton (2012, this volume). Nobre (2011, personal communication) made the following comments:

Prompted past a need to create a scientific framework to better understand these circuitous processes, the workshop on Vegetation and Climatic Interactions in Amazonia in 1985 helped advance an integrated World systems arroyo. The Briefing recommendations evolved into central Large-Calibration Biosphere Temper Experiment in Amazonia (LBA) themes of agreement the Amazon every bit a regional entity of the Earth system and of studying how climate and land cover changes can change its concrete, chemic and biological functioning.

C. Nobre, personal communication, 2011

Lovelock'south Gaia hypothesis advanced understanding that a planet with abundant life will have an atmosphere with 'thermodynamic disequilibrium' and that "Earth is habitable because of complex linkages and feedbacks between the atmosphere, oceans, land, and biosphere", which helped shape ESS (Lawton, 2001, p. 1965). The remainder of this department focuses on the genesis and evolution of ESS.

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Globe SYSTEM SCIENCE

R.C. Selley , in Encyclopedia of Geology, 2005

Earth System Science and the 'Gaia' Hypothesis

Since the 1970s James Lovelock developed the Gaia hypothesis, named after the ancient Greek goddess of the Earth ( Run into GAIA). Every bit originally conceived the 'Gaia' concept envisages the Globe as a super-organism that operates to regulate its own environment, principally temperature, to proceed it habitable for the biosphere. Lovelock has never argued that the biosphere consciously anticipates environmental change, but only that it automatically responds to it. Notwithstanding some sections of the public accept construed information technology that style, and in the popular mind Gaia gained a quasi-mystical connotation, enhanced by its name. The cracking value of the Gaia hypothesis is that it presents the interdependence of the constituents of the geosphere in a media-friendly fashion. Globe organization science also involves a holistic approach to the geosphere, but without the 'ghost in the motorcar'. Nonetheless Amazon, the internet book shop, nevertheless classifies books on Earth organization scientific discipline under 'Religion and Spirituality > New Historic period > Earth-Based Religions > Gaia'.

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Self-Organization

D.G. Green , ... T.G. Leishman , in Encyclopedia of Ecology, 2008

Self-Organization in the Biosphere

Arguably the nigh ambitious ecological theory based on self-organization is the Gaia hypothesis, which postulates that the biosphere itself evolves to a homeostatic state. Lovelock suggested the Daisyworld model equally an illustration of how this procedure might occur. On the hypothetical Daisyworld, black and white daisies compete for space. Although both kinds of daisies grow best at the same temperature, black daisies blot more than heat than white daisies. When the Dominicus shines more brightly, heating the planet, white daisies spread, and the planet cools again. When the Lord's day dims, the blackness daisies spread, warming the planet. In this way, competitive interactions between daisies provide a homeostatic mechanism for the planet every bit a whole.

The idea behind Gaia is that ecosystems volition survive and spread more finer if they promote the abiotic conditions required for their own persistence. If and so, ecosystems might gradually evolve to be increasingly robust, and if this happened on a global scale, and so the biosphere itself might carry every bit a self-regulating system. However, evidence for Gaian processes in real ecosystems remains tenuous and their theoretical plausibility is disputed.

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Symbiosis in Ecology and Evolution

Kent A. Peacock , in Philosophy of Environmental, 2011

4.iv Natural Selection and the Symbiome

Some of the things I am going to say in the following department are going to sound like a defense of the Gaia hypothesis against the sort of selectionist critique that (every bit noted above) seems to have given pause even to Lovelock himself. Still, it is non the purpose of this paper to fully explicate the Gaia hypothesis of James Lovelock and Lynn Margulis [ Lovelock, 1988; Lovelock and Margulis, 1974; Margulis, 1998]. (Thinking of Gaia as a mutualistic symbiome rather than equally a single living organism may make the concept more palatable for some.) The major aim of this department is to explain how the evolution of symbiotic associations of organisms (whether Gaia or something on a less one thousand scale) could exist favoured past natural option. Some of what I say hither takes advantage of an assay past Timothy Lenton [1998].

I will take as my nominal target a token of Dawkins' influential critique of the Gaia hypothesis:

I don't retrieve Lovelock was articulate—in his first book, at least—on the kind of natural-selection procedure that was supposed to put together the adaptive unit of measurement, which in his case was the whole world. If y'all're going to talk well-nigh a unit of measurement at any level in the hierarchy of life as being adaptive, then in that location has to exist some sort of option going on amidst cocky-replicating information. And we have to inquire, What is the equivalent of DNA? What are the units of code? What are the units of copyme lawmaking which are being replicated? … I don't call up for a moment that information technology occurred to Lovelock to inquire himself that question. And so I'm skeptical of the rhetoric of the Gaia hypothesis, when it comes downwardly to item applications of it, similar explaining the amount of methane there is in the atmosphere, or saying there volition be some gas produced by bacteria which is proficient for the world at big and so the leaner become to the trouble of producing information technology, for the adept of the world. That can't happen in a Darwinian world, equally long every bit nosotros think that natural selection is going on at the level of individual bacterial genes. Because those private bacteria who don't put themselves to the trouble of manufacturing this gas for the good of the globe will do amend. Of course, if the private bacteria who manufacture the gas are actually doing themselves better by doing and then, and the gas is simply an incidental consequence, apparently I have no problem with that, but in that case you lot don't need a Gaia hypothesis to explain information technology. You explain it at the level of what's expert for the individual bacteria and their genes. [Dawkins, 1995]

In fairness to Dawkins, these remarks were apparently made ex tempore at a briefing. Even so, they illustrate a lack of clarity about symbiosis that is endemic to the thinking of evolutionary biologists.

The first thing to articulate out of the way is to remind ourselves that we need to accept care to avoid teleological language which is applicable merely to conscious organisms such as humans who can plan alee on the basis of imaginative representations of goals. Dawkins, who should know better, gets sloppy this mode when he suggests that his hypothetical bacteria might produce a gas "for the good of the world". No leaner produce gases or annihilation else for the sake of anything, even themselves, while humans do all sorts of things for the sake of goals and purposes. (Information technology would probably exist improve as well if biologists were to avoid the term "altruism" for the self-sacrificial behavior that sometimes occurs in mutualistic functioning, since that word is most accurately applied to sure man motivations.)

In a mutualistic organization a species of bacteria may well take the function of producing a certain gas that facilitates the operation of the arrangement as a whole; functional language is perfectly appropriate for coordinated living systems from protozoans to ecosystems [Allen, 2004]. But the fact that a organisation has evolved in such a style that some of its components have recognizable functions in the economy of the whole does not mean that they have purposes in the sense that things done intentionally by humans have a purpose, nor that they have their function for the sake of the whole. (This was expressed clearly past Simpson; come across [Simpson, 1953, p. 181].) To say that (for case) the cells in my kidneys cooperate in a sure way is to say that they happen to part in concert in a certain way, not that they cooperate in the sense that humans can (on selected occasions) cull to cooperate. My kidneys have the function of eliminating excess water and certain toxins from my torso, but they do these things because these activities are supported by a circuitous network of feedback loops; they do not practise them for my sake or even for their ain. This is an important part of the answer to Paley [Paley, 1802] and other champions of "intelligent design": the fact that parts of a complex system have recognizable functions does not by itself imply that they were products of intentionality.

A much tougher question is to say what constitutes a replicator. Dawkins thinks that it does not make sense to say that Gaia has a genome. But of form Gaia has a genome; the genome of Gaia and any other sort of symbiotic complex is comprised of the combined DNA and RNA of all of the myriad organisms of which information technology is composed. A distributed genome is very common at the eukaryotic cellular level. By now there is no controversy nigh the fact that in that location is cytoplasmic Dna, namely the DNA belonging to organelles of endosymbiotic origin such as the mitochondria and plastids. The genome of nearly all metazoan cell lines consists non just of nuclear genes merely of the genetic heritage of an often bewilderingly complex suite of endosymbiotes. The genome of an organism does not take to be concentrated in one spot within the organism, and information technology rarely is.

A good analogy of this fact is the protozoan (or more than properly protist) Mixotricha paradoxa, an extraordinarily beautiful organism often cited by Margulis (e.one thousand., in [Margulis, 1998; Margulis and Sagan, 2001]) as an exemplar of symbiogenesis. Thousand. paradoxa lives in the gut of certain termites, and apparently serves its hosts by digesting cellulose and lignin. But it is a symbiote built out of symbiotes: besides equally its own nucleus, each M. paradoxa contains several hundred thousand individuals of at least four other species of leaner [Margulis and Sagan, 2001]. (Curiously, the one blazon of symbiotic organelle it does not contain is the mitochondrion, probably because the termite gut is anoxic.) Each private Chiliad. paradoxa is a populous community, cooperating as a mutualistic whole. So what, in such a case, is the unit of selection?

Dawkins is right that any chunk of genetic code that in upshot says "make more than of me" can be a replicator and will succeed in being replicated if it says this in only the right way to resonate with the demands of its surround. Even so, networks of cooperative behaviors tin can and frequently are sufficiently successful that they are amplified past natural choice into a coherent, reproducing whole. This can occur non merely in the cases of endosymbiosis studied past Margulis; complex associations of metazoa can form such symbiotic networks equally well, some of which may be more tightly coupled (that is, causally interactive) than others. To further complicate the story, it is increasingly evident that complex metazoa such as mammals are host to a rich array of microbial symbiotes, so much then that microbiologists are starting time to draw multicellular organisms as metagenomic [Grice et al., 2008; Ley et al., 2008]. If a symbiotic network is sufficiently coherent and coordinated that it reproduces as a whole, then its unabridged genetic lawmaking is a replicator. Then the question of the unit of pick, the question of what is "seen" by natural option, is not simple; information technology is not just the gene (whatever that is) unless by "gene" one means simply whatever replicator. A sufficiently well coordinated symbiotic clan tin itself become a unit of pick.

Most of Dawkins' objections to Gaia utilise to Mixotricha paradoxa likewise, and if he were correct, there ought to exist no such thing. In fact, the way that M. paradoxa reproduces tin can give united states some insight into the sense in which a hypothetical planetary-scale symbiotic unit could evolve. In symbiotic protists like M. paradoxa the orchestration of reproduction is complex and non yet well-understood. Notwithstanding, there is no reason to suppose that all the component symbionts of such organisms reproduce in perfect concert, even though the host cell is capable of division every bit a unit of measurement. Endobacterial symbionts within a larger complex could well run through many reproductive cycles of their own during one reproductive cycle of the larger circuitous. Their survival would depend upon adapting to the constraints within the larger organism, just as all organisms on Earth take to adapt to the often-inorganic but sometimes organic constraints of the larger world. (An important example of such a constraint is climate, which might best be described equally an organically-mediated inorganic constraint. Clearly when ane is speaking of an environmental parameter such equally temperature, which is partially controlled by solar input and partially controlled by carbon dioxide concentration, the dividing line between the organic and the inorganic is often fuzzy.) To a single bacterium within G. paradoxa, one jail cell generation of its host is an entire cosmological cycle which defines a globe to which the bacterium must accommodate like whatever other organism in nature. Such symbionts inside an organism such every bit Chiliad. paradoxa would often be subject to natural selection that would tend to favour their ability to contribute to the economic system of the whole organism. Circuitous symbiotic associations like One thousand. paradoxa therefore also tin evolve piecemeal in response to internal constraints every bit well equally all at once in the usually understood style, in which the blended organism evolves as a whole in response to external constraints. Ane tin therefore distinguish between external development (which is well-studied) and internal development—evolution of the components of a complex symbiotic association in response to survival challenges and opportunities acting internally to the association.

A cardinal divergence between Gaia (every bit hypothesized by Lovelock and Margulis) and the kinds of organisms to which the usual model of natural selection applies is, therefore, that Gaia does not reproduce as a unit every bit do its component organisms, including M. paradoxa. Rather, Gaia evolves because evolution occurs within it, just as it does within M. paradoxa. Gaia reproduces gradually, role by part, in a process of growth, regeneration, adaptation, and decay, almost like an organic version of Neurath'southward boat of knowledge which is rebuilt piece past piece as information technology floats along. Gaia as a whole adapts to its external environs over millions of years in a piecemeal, not-perfectly-coordinated way equally its component organisms adjust to the constraints of the external environment and the internal constraints imposed on them by the other organisms in the system. In a remarkably English language manner, Gaia muddles through and remains tough and resilient despite its jury-rigged nature. Although the details must be very complex and may never be fully elucidated, there is no reason why we cannot suppose that Gaia (viewed as something like a planetary-scale 1000. paradoxa) cannot be supposed to evolve in the piecemeal way that a circuitous symbiotic association similar G. paradoxa tin evolve, even though it neither has a nucleus which partially coordinates its activities, nor reproduces as a unit of measurement the style a protist can.

Now, Dawkins suggests that we imagine that some mutant bacteria happen to start producing a certain gas that is beneficial to the symbiotic complex every bit a whole. He makes a very odd claim: "those private bacteria who don't put themselves to the trouble of manufacturing this gas for the good of the earth will practise improve." (This is more or less Garrett Hardin's tragedy of the commons at the cellular level.) But it should be articulate that this is not necessarily the case; an organism manufacturing some component that increases the overall suitability of the environment for that organism could very well increment the reproductive success of that organism even if the manufacturing procedure has costs and risks associated with information technology. There is no guarantee that this would happen in all cases, but in that location is no a priori reason that information technology would not, either.

Some parasitical "free-riders" can be tolerated and then long as the functionality of the system is maintained; indeed, some parasitism may benefit the system in indirect means if it maintains variability. But if all organisms in an ecosystem are parasitical in the sense that they exercise non put themselves to the problem of contributing something to the system, they certainly volition not exercise meliorate since the whole arrangement will ultimately degrade.

Perhaps the notion of a price-benefit assay would exist helpful here. Whatsoever conceivable activity by an organism has a cost. This need not be only in terms of energy and materials; adaptation to any item environment also exposes an organism to the hazards typical of that surroundings, such as the predators peculiar to it. In that location are as well opportunity costs: if an organism becomes adapted to the Arctic common cold, for instance, then it may have given up survival options suitable to warmer weather. It is simple that cooperative behaviour carries costs and risks precisely equally Hardin indicated; for instance, if the organism shares some of its resources with others it will accept less for itself, and information technology opens itself up to the hazard that information technology may exist out-reproduced or otherwise out-competed past others of its species or other species who are less inclined to share the goods. However, an activeness tin can be advantageous even if information technology has a cost, so long every bit its benefits outweigh its cost, while failure to cooperate may have costs as well, which could include (as in Hardin's tragic scenario) subversion of the very ecology conditions that made life possible for that organism in the first place. Once more, at the risk of repetition, the existence of a co-operative symbiotic modality does not imply intentionality (as with co-performance between humans) but rather coherence of functionality.

As Lenton observes,

Organisms possess surroundings-altering traits considering the do good that these traits confer (to the fitness of the organisms) outweighs the price in free energy [emphasis added] to the individual [Lenton, 1998, p. 440].

This remark suggests a clarification of the sense in which benefit flows back to a symbiont. The nearly general sense of "benefit" to an organism is the availability of costless free energy; this can translate into reproductive opportunities or only an increased survival probability for the individual (since more free energy allows for a wider repertoire of survival strategies and modalities). We meet here over again an instance in which thermodynamics can illuminate the workings of evolution.

If Hardin'south scenario were the normal design—that is, if life typically subverts the conditions for its existence—how could at that place be life on Earth at all? Earthly life has proved remarkably resilient for over 3.5 billion years, despite celestial impacts, episodes of massive volcanism (and the occasional runaway greenhouse catastrophes possibly consequent upon them [Ward, 2007]), and steadily increasing solar output. This could just be possible if the persistence of complex life is somehow probabilistically favoured within the wide range of physical atmospheric condition that have been available on Earth for nearly the past four billion years, and that is simply possible if life (despite the abiding recurrence of owned parasitism at all scales from the viruses to human being society) has had (so far at least) a net tendency to co-operate in order to maintain the atmospheric condition necessary for its continuance. This is especially clear if we sympathise parasitism from the biophysical (thermodynamic) point of view as something that results in the physical degradation of the host; if life on World in net degraded its habitats then information technology would have destroyed itself long agone. Furthermore, if life in internet were balanced on the pocketknife-edge of commensalism, it is hard to understand how such a precarious state could accept persisted for so long. A planetary-calibration, rough-and-ready mutualism seems to be the simply possibility, and this observation could be thought of every bit a minimal Gaia hypothesis.

Suppose that the cost of a new trait is that it requires cocky-sacrificial behavior for some members of the species. If a strain of mutant organisms merely commits suicide en masse then its evolutionary story is over. Withal, if the self-sacrificial behavior greatly facilitates the reproduction of the survivors, even if at that place are rather few of them, then it will tend to be amplified past natural selection. The importance of mechanisms of this sort has been emphasized by Bonner who has described, for instance, the cocky-sacrificial behavior of slime mold amoeba (in vast numbers) in the formation of a slime mold fruiting body [Bonner, 1998]. There is aught unusual well-nigh this sort of thing; it occurs throughout nature from the bacterial level on upward. Over again, the fact that cooperative behaviour has costs and risks does not imply that it puts its possessor at a selective disadvantage, then long as there is a sufficient reward for the behaviour as well.

Apparently-donating behavior need not be explained merely as "kin choice"; an organism need non exist in a mutualism merely with its cousins. It could exist in mutualism with any other conceivable form of life at all, and so long as the cyberspace outcome is to provide a modality of survival for the organism. Here, by the way is the ground for so-called group choice, which is cipher more than selection in favour of mutualistic symbiosis. This is a signal that even the nigh sympathetic and well-informed apologists for group pick do not bring out every bit clearly equally they could [Sober and Wilson, 1998]. (Whether species selection tin be understood in symbiotic terms is a different and hard question since it is not clear that a species tin can always be thought of as a symbiome; I will not address this question further hither. [Stanley, 1979].)

Dawkins' distressingly sloppy argument is above all a crashing non sequitur— for from the fact that cooperation must inevitably take costs and incur risks information technology does not follow that it cannot accept benefits as well, and indeed net benefits. What actually matters is the timing of those benefits: the feedback from the surround has to return to the organism presently plenty to brand a deviation to its reproductive success or probability of survival. Therein lies the real tragedy of Hardin'due south medieval eatables: a social pathology that prevented sufficient rewards for cooperative behaviour from flowing back to the beleaguered peasants presently enough for those rewards to make a difference to their well-being.

Natural pick tin can be understood as a procedure involving feedbacks. If a trait increases reproductive success that process can be described as the amplification of the trait by positive feedback from the environment. On the other hand, if a trait triggers a chain of events that decreases the probability of its own recurrence then it volition be damped out past that negative feedback from the environment. In order for the effect of the altered trait on the surroundings to make any departure to reproductive success, it has to feed back to the organism in fourth dimension to affect its reproduction; it does non have to feed back within only one reproductive cycle, but the feedback cannot take forever or be and so attenuated that it makes no deviation to the reproductive or survival probability of the organism. (As in so many endeavors, timing is virtually everything.) Such feedbacks tin can certainly reward cooperative too as competitive behaviour. And once once again, by "cooperative" behavior we do non mean activity that is motivated by warm feelings of fellowship, just coherence of functionality.

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Biogeochemical Cycling

Raina M. Maier , in Ecology Microbiology (2d Edition), 2009

14.1.ii Gaia Hypothesis

In the early 1970s, James Lovelock theorized that Globe behaves like a superorganism, and this concept developed into what is now known as the Gaia hypothesis . To quote Lovelock (1995): "Living organisms and their material environment are tightly coupled. The coupled organization is a superorganism, and as it evolves in that location emerges a new property, the ability to self-regulate climate and chemistry." The bones tenet of this hypothesis is that Earth's physicochemical properties are self-regulated then that they are maintained in a favorable range for life. Equally bear witness for this, consider that the sun has heated upwardly past 30% during the past 4–5 billion years. Given Earth's original carbon dioxide–rich atmosphere, the average surface temperature of a lifeless Globe today would be approximately 290°C (Table 14.2). In fact, when one compares Earth's present-24-hour interval temper with the atmospheres constitute on our nearest neighbors Venus and Mars, one tin meet that something has drastically affected the development of Earth'south atmosphere. According to the Gaia hypothesis, this is the development and continued presence of life. Microbial activity, and later the advent of plants, take changed the original heat-trapping carbon dioxide–rich temper to the present oxidizing, carbon dioxide–poor atmosphere. This has allowed Earth to maintain an average surface temperature of 13°C, which is favorable to the life that exists on Globe.

Table xiv.2. Atmosphere and Temperatures Found on Venus, Mars, and Earth Plane

Gas Venus Mars Earth without life Globe with life
Carbon dioxide 96.five% 95% 98% 0.03%
Nitrogen 3.5% 2.vii% 1.nine% 9%
Oxygen Trace 0.13% 0.0 21%
Argon 70ppm 1.vi% 0.1% ane%
Methyl hydride 0.0 0.0 0.0 1.7ppm
Surface temperature (°C) 459 −53 290 ± 50 13

Adapted from Lovelock, 1995.

Copyright © 1995

How do biogeochemical activities relate to the Gaia hypothesis? These biological activities take driven the response to the slow warming of the sun, resulting in the major atmospheric changes that have occurred over the last four–5 billion years. When Earth was formed 4–5 billion years agone, a reducing (anaerobic) atmosphere existed. The initial reactions that mediated the germination of organic carbon were abiotic, driven past big influxes of ultraviolet (UV) light. The resulting reservoir of organic matter was utilized past early anaerobic heterotrophic organisms. This was followed by the development of the ability of microbes to set up carbon dioxide photosynthetically. Evidence from stromatolite fossils suggests that the ability to photosynthesize was developed at to the lowest degree three.5 billion years agone. Stromatolites are fossilized laminated structures that have been constitute in Africa and Commonwealth of australia (Fig. 14.ane). Although the topic is hotly debated, in that location is evidence that these structures were formed past photosynthetic microorganisms (first anaerobic, and so cyanobacterial) that grew in mats and entrapped or precipitated inorganic fabric as they grew (Bosak et al., 2007).

Effigy 14.one. An example of a living stromatolite (left) and a stromatolite fossil (right).

 From (left) Reynolds, 1999 and (right) Farabee, 2008. Copyright © 2008

The evolution of photosynthetic organisms tapped into an unlimited source of free energy, the sun, and provided a mechanism for carbon recycling, that is, the get-go carbon cycle (Fig. fourteen.ii). This kickoff carbon cycle was maintained for approximately i.five billion years. Geologic evidence and then suggests that approximately ii billion years ago, photosynthetic microorganisms developed the ability to produce oxygen. This allowed oxygen to accumulate in the atmosphere, resulting, in time, in a alter from reducing to oxidizing weather condition. Further, oxygen accumulation in the atmosphere created an ozone layer, which reduced the influx of harmful UV radiation, allowing the evolution of college forms of life to brainstorm.

FIGURE 14.2. The carbon bicycle is dependent on autotrophic organisms that gear up carbon dioxide into organic carbon and heterotrophic organisms that respire organic carbon to carbon dioxide.

At the same time that the carbon wheel evolved, the nitrogen cycle emerged because nitrogen was a limiting element for microbial growth. Although molecular nitrogen was abundant in the temper, microbial cells could not directly utilize nitrogen every bit Due north2 gas. Cells crave organic nitrogen compounds or reduced inorganic forms of nitrogen for growth. Therefore, under the reducing weather condition found on early Earth, some organisms developed a machinery for fixing nitrogen using the enzyme nitrogenase. Nitrogen fixation remains an important microbiological process, and to this day, the majority of nitrogenase enzymes are totally inhibited in the presence of oxygen.

When considered over this geologic time scale of several billion years, information technology is apparent that biogeochemical activities have been unidirectional. This means that the predominant microbial activities on earth have evolved over this long period of fourth dimension to produce changes and to reply to changes that have occurred in the atmosphere, namely, the appearance of oxygen and the subtract in carbon dioxide content. Presumably these changes will go along to occur, but they occur so slowly that nosotros exercise non take the capacity to discover them.

One can likewise consider biogeochemical activities on a more contemporary time scale, that of tens to hundreds of years. On this much shorter time scale, biogeochemical activities are regular and cyclic in nature, and information technology is these activities that are addressed in this chapter. On the one hand, the presumption that Globe is a superorganism and can answer to drastic environmental changes is heartening when one considers that homo action is effecting unexpected changes in the atmosphere, such every bit ozone depletion and buildup of carbon dioxide. However, information technology is important to point out that the response of a superorganism is necessarily slow (thousands to millions of years), and as residents of Globe we must exist sure not to overtax Earth's ability to respond to modify by artificially changing the environment in a much shorter time frame.

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