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It seems reasonable to suppose that in order to discuss, much less discover, the '''Origin of life''' one must first answer the question, "What is [[Life]]?"  Yet, as discussed in the article, [[Life]], we should pose that question more coherently by asking, "What processes give rise to the activity of living?"  In searching for the origin of life ''o planet Earth'', we need to search for the beginnings of the physico-chemical processes that we know underpin the activity of living and how those led to the first cells, the basic building blocks and working units of all living things on Earth. Indeed we must search for the characteristics of the earliest cells from which all current living things descended. Because we must work backward to a time nearly four billion years ago, we will find little, but not nothing,<ref name=hazen>Hazen RM. (2005) Genesis: The Scientific Quest for Life's Origin. Washington,DC: Joseph Henry Press. ISBN 0309094321</ref>&nbsp;&nbsp;in the way of remains to examine. We can hypothesize, and submit those hypotheses to existing knowledge of earth's early conditions and to experiments attempting to reproduce those conditions. We can narrow our hypotheses and search-paths by dissecting out the most basic and essential physico-chemical process common to all known living things &mdash; the universal biophysics,<ref name=schneider05> Schneider ED, Sagan D (2005) ''Into the Cool: Energy Flow, Thermodynamics, and Life.'' Chicago: The University of Chicago Press. ISBN 0-226-73937-6 [http://www.intothecool.com/ Chapter Excerpts and Reviews]</ref> biochemistry<ref name=pacepnas>[http://www.pnas.org/cgi/content/full/98/3/805 The universal nature of biochemistry, by Norman R. Pace]</ref> and metabolism<ref>Smith E., Morowitz HJ. (2004) Universality in intermediary metabolism.  Proc Natl Acad Sci U S A 101:13168-13173. PMID 15340153 [http://dx.doi.org/10.1073/pnas.0404922101 Full-Text]</ref> of living things &mdash; because as conserved core processes they have the greatest probability of embryonic status. We search for the origin of a system we recognize as living in virtue that it has the informational content and information-processing ability to remain in a near steady-state as a self-organized system of hierarchical robust modular molecular networks, where the networks operate autonomously in their own behalf, to offset responses to perturbations, and facilitate the system's reproducing itself.  We search for the origin of a system enabled by influx of energy and matter and by a more than compensatory efflux of waste (disorder), thereby sustaining and exploiting a dynamically organized state far from the equilibrium state of randomness. Finally, we search for the origin of a system capable, through its self-reproductive ability, of participating in the evolutionary processes<ref name=jablonkalamb>Jablonka E, Lamb MJ (2005) ''Evolution in Four Dimension: Genetic, Epigenetic, Behavioral, and Symbolic Variation in the History of Life.'' Cambridge: The MIT Press</ref> that enable transgenerational evolution of the species to which it belongs in adapting to changing environments.
In order to discuss, much less discover, the '''Origin of life''', we must first answer the question, "What is [[Life]]?"  We can pose that question more coherently by asking, "What essential processes underpin the activity of living?"  Knowing the fundamental physico-chemical processes that underpin the activity of all living systems gives us a starting point for making observations, generating hypotheses, and performing experiments in the search for life’s origin &mdash; for those processes somehow must have given rise to the first cells, the basic building blocks and working units of all living things on Earth. We must discover  the characteristics of the earliest cells from which all current living things descended.  
 
Because we must look backward to a time nearly four billion years ago, we will find little, but not nothing,<ref name=hazen>Hazen RM. (2005) Genesis: The Scientific Quest for Life's Origin. Washington,DC: Joseph Henry Press. ISBN 0309094321</ref>&nbsp;&nbsp;in the way of remains to examine. We can hypothesize, and submit those hypotheses to existing knowledge of earth's early conditions and to experiments attempting to reproduce those conditions. We can narrow our hypotheses and search-paths by dissecting out the most basic and essential physico-chemical processes common to all known living things &mdash; the universal biophysics,<ref name=schneider05> Schneider ED, Sagan D (2005) ''Into the Cool: Energy Flow, Thermodynamics, and Life.'' Chicago: The University of Chicago Press. ISBN 0-226-73937-6 [http://www.intothecool.com/ Chapter Excerpts and Reviews]</ref> &nbsp;&nbsp;biochemistry<ref name=pacepnas>[http://www.pnas.org/cgi/content/full/98/3/805 The universal nature of biochemistry, by Norman R. Pace]</ref>&nbsp;&nbsp;and metabolism<ref>Smith E., Morowitz HJ. (2004) Universality in intermediary metabolism.  Proc Natl Acad Sci U S A 101:13168-13173. PMID 15340153 [http://dx.doi.org/10.1073/pnas.0404922101 Full-Text]</ref>&nbsp;&nbsp;of living things &mdash; because as conserved core processes they have the greatest probability of embryonic status.  
 
We search for the origin of a system we recognize as living in virtue that it has the informational content and information-processing ability to remain in a near steady-state as a self-organized system of hierarchical robust modular molecular networks, where the networks operate autonomously in their own behalf, to offset responses to perturbations, adapt to changing conditions, and facilitate the system's reproducing itself.  We search for the origin of a system enabled by influx of energy and matter and by a more than compensatory efflux of waste (disorder), which thereby permits sustaining and exploiting a dynamically organized state far from the equilibrium state of randomness. Finally, we search for the origin of a system capable, through its self-reproductive ability, of participating in the evolutionary processes<ref name=jablonkalamb>Jablonka E, Lamb MJ (2005) ''Evolution in Four Dimension: Genetic, Epigenetic, Behavioral, and Symbolic Variation in the History of Life.'' Cambridge: The MIT Press</ref>&nbsp;&nbsp;that enable transgenerational evolution of the species to which it belongs, adapting to changing environments.
 
We do not know the origin of life on Earth.  We do have plausible scenarios.


==The historical background of 'origin' thinking==
==The historical background of 'origin' thinking==

Revision as of 20:14, 25 May 2007

In order to discuss, much less discover, the Origin of life, we must first answer the question, "What is Life?" We can pose that question more coherently by asking, "What essential processes underpin the activity of living?" Knowing the fundamental physico-chemical processes that underpin the activity of all living systems gives us a starting point for making observations, generating hypotheses, and performing experiments in the search for life’s origin — for those processes somehow must have given rise to the first cells, the basic building blocks and working units of all living things on Earth. We must discover the characteristics of the earliest cells from which all current living things descended.

Because we must look backward to a time nearly four billion years ago, we will find little, but not nothing,[1]  in the way of remains to examine. We can hypothesize, and submit those hypotheses to existing knowledge of earth's early conditions and to experiments attempting to reproduce those conditions. We can narrow our hypotheses and search-paths by dissecting out the most basic and essential physico-chemical processes common to all known living things — the universal biophysics,[2]   biochemistry[3]  and metabolism[4]  of living things — because as conserved core processes they have the greatest probability of embryonic status.

We search for the origin of a system we recognize as living in virtue that it has the informational content and information-processing ability to remain in a near steady-state as a self-organized system of hierarchical robust modular molecular networks, where the networks operate autonomously in their own behalf, to offset responses to perturbations, adapt to changing conditions, and facilitate the system's reproducing itself. We search for the origin of a system enabled by influx of energy and matter and by a more than compensatory efflux of waste (disorder), which thereby permits sustaining and exploiting a dynamically organized state far from the equilibrium state of randomness. Finally, we search for the origin of a system capable, through its self-reproductive ability, of participating in the evolutionary processes[5]  that enable transgenerational evolution of the species to which it belongs, adapting to changing environments.

We do not know the origin of life on Earth. We do have plausible scenarios.

The historical background of 'origin' thinking

Origin of planet earth and its pre-biotic characteristics

Pre-replicator chemical evolution

Pre-biotic pre-replicator chemical evolution as prelude to origin of living systems. See, for example:

Also:

  • Danchin 2007[9]

The first replicators

Sources of energy

Community metabolism

Coding for amino acids

The RNA World

Rampant horizontal gene transfer hypothesis

RNA to DNA transition

Emergence of Darwinian struggle

Emergence of cells

Oldest fossils

References

Citations

  1. ↑ Hazen RM. (2005) Genesis: The Scientific Quest for Life's Origin. Washington,DC: Joseph Henry Press. ISBN 0309094321
  2. ↑ Schneider ED, Sagan D (2005) Into the Cool: Energy Flow, Thermodynamics, and Life. Chicago: The University of Chicago Press. ISBN 0-226-73937-6 Chapter Excerpts and Reviews
  3. ↑ The universal nature of biochemistry, by Norman R. Pace
  4. ↑ Smith E., Morowitz HJ. (2004) Universality in intermediary metabolism. Proc Natl Acad Sci U S A 101:13168-13173. PMID 15340153 Full-Text
  5. ↑ Jablonka E, Lamb MJ (2005) Evolution in Four Dimension: Genetic, Epigenetic, Behavioral, and Symbolic Variation in the History of Life. Cambridge: The MIT Press
  6. ↑ Dyson F (1982) A model for the origin of life. See Dyson (1982) J Mol Evol 18:344-350
  7. ↑ Post RL. (1990) The origin of homeostasis in the early earth. Journal of Molecular Evolution 31:257-64 Summary and Link to Full-Text.
  8. ↑ Galimov EM. (2004) Phenomenon of life: between equilibrium and non-linearity. Orig.Life Evol Biosph. 34:599-613.
  9. ↑ Danchin A, Fang G, Noria S. (2007) The extant core bacterial proteome is an archive of the origin of life. Proteomics 7:875-889 PMID 17370266
  10. ↑ Sayer RM. (2006) Self-organizing proto-replicators and the origin of life. Biosystems PMID 17014952
  11. ↑ Deamer D, Singaram S, Rajamani S, Kompanichenko V, Guggenheim S. (2006) Self-assembly processes in the prebiotic environment. Philos Trans R Soc Lond B Biol Sci 361:1809-1818 PMID 17008220
  12. ↑ Szathmary E. (2006) The origin of replicators and reproducers. Philos Trans R Soc Lond B Biol Sci 361:1761-1776 PMID 17008217
  13. ↑ Davies P. The FIFTH MIRACLE: The Search for the Origin and Meaning of Life (Paperback) Simon & Schuster ISBN-10: 068486309X ISBN-13: 978-0684863092

External links

Further reading

  • Forterre P (2006) Three RNA cells for ribosomal lineages and three DNA viruses to replicate their genomes: A hypothesis for the origin of cellular domain PNAS 103:3669-3674
  • Davies P. (2000) The Fifth Miracle: Search for the Origin and Meaning of Life. Simon & Schuster ISBN 978-0684863092
  • From The New York Times Book Review, by Lee Smolin: "If you are going to read only one book on the origin of life, seriously consider this one. From Scientific American: "His thesis is that 'the first terrestrial organisms lived deep underground, entombed within geothermally heated rocks in pressure-cooker conditions.' Davies also looks at the theories that life began by chemical assembly in a watery medium and that it came to the earth from space in the form of already viable microbes--the panspermia hypothesis.

See also

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