Origin of life

From Citizendium
Revision as of 19:17, 10 August 2008 by imported>Anthony.Sebastian (→‎"A quantum recipe for [the origin of] life": language work; wiki-links)
Jump to navigation Jump to search
This article is developing and not approved.
Main Article
Discussion
Related Articles  [?]
Bibliography  [?]
External Links  [?]
Citable Version  [?]
Gallery [?]
Video [?]
Signed Articles [?]
 
This editable Main Article is under development and subject to a disclaimer.

In a scientific context, 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 earliest 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 as a spatially compartmentalized near-steady-state self-organized dynamical 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 thermodynamically open system enabled by influx of energy and matter and by a more than compensatory efflux of waste (disorder), which thereby complies with the second law of thermodynamics and 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],[6]  that enable transgenerational evolution of the species to which it belongs, adapting to changing environments.

Scientists do not know the origin of life on Earth. They do have pieces of the puzzle, however, and many conflicting plausible scientific scenarios.

The history of scientific 'origins of life' thinking

"A quantum recipe for [the origin of] life"

Theoretical physicist, cosmologist, astrobiologist and science popularizer, Paul Davies [7] has imagined a "quantum recipe" for the origin of life: [8]

To take up [physicist Erwin] Schrödinger's suggestion [....that quantum mechanics, or some variant of it, would soon solve the riddle of life....],[9] a radical solution to the problem, 'What is life?' could be that quantum mechanics enabled life to emerge directly from the atomic world, without the need for complex intermediate chemistry. Life must have a chemical basis: organic molecules provide the hardware for biology. But what about the software? [8]

The software, Davies argues, resides in quantum information. "....to get life started all you need is to replicate information." [8] He argues that, at the quantum level [of reality], information processing can proceed much more rapidly, by comparison presumably with chemical reactions, can achieve gains in information processing performance through such quantum capabilities as tunneling, superposition, and entanglement. He proceeds to conjecture on the replication of the information in an atomic system through a series of interactions, the information in the systems residing possibly in binary form "....making use of the spin orientation of an electron or atom for example." [8] He asserts that quantum mechanics can thus make discrete 'genetic' information.

Davies refers to his conjectured quantum information replicator as "atomic Adam" and speculates on the best environments where some such "atomic Adam[s]" might exist. He argues that when a population of such quantum information replicators arises, expect variation in the fidelity of replication because of the quantum uncertainty principle. Given variation, an evolution of the information by means of darwinian-wallacean natural selection, or survival of the fittest replicators, might occur in the prevailing environment. "....and the great darwinian game could begin." [8]

Davies then asks, given the reality of quantum information replicators in a darwinian reproductive-type domain, how 'organic' life arose? He supposes that "At some stage, quantum life could have co-opted large organic molecules for back-up memory." How that 'great leap' might have occurred Davies offers no plausible description, except to say that information in one medium does not preclude translation to other media. Not that the medium of organic chemistry strays far from the underpinnings of its quantum chemical medium.

Once that transfer of information occurs — from quantum to chemical information — expect a loss in rapidity of information processing, but also expect greater stability in the organic molecules, and greater versatility, and greater complexity. Those compensations might ensure the dominance of organic living systems, given natural selection, and its enabling of the exploitation of diverse environments.

Davies seems to worry most about the issue of complexity of quantum life:

How complexity emerges in quantum systems is a subject still in its infancy, but the principles involved could be illuminated by applying algorithmic complexity theory to quantum information theory. [8]

We might ask the question how much complexity must precede the transfer of quantum information to organic molecular information, given the potential for natural selection, and other evolutionary forces — not to mention autopoiesis — to enable the emergence of organic complexity?

Origin of planet Earth and its pre-biotic characteristics

Pre-biotic chemistry and the origin of organic molecules

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

The first molecular 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. Reid RGB. (2007) Biological Emergences: Evolution by Natural Experiment. A Bradford Book, Cambridge. ISBN 0-262-18257-2
  7. Paul Davies Website
  8. 8.0 8.1 8.2 8.3 8.4 8.5 Davies P. (2005) A Quantum Recipe for Life. Nature 437:819.
    • From Article:  [At the time of this article:] Paul Davies is a physicist in the Australian Centre for Astrobiology, Macquarie University, Sydney, and author of The Origin of Life (Penguin, 2003)
  9. Note: Not a direct quote from schrodinger's book.
  10. Dyson F (1982) A model for the origin of life. See Dyson (1982) J Mol Evol 18:344-350
  11. Post RL. (1990) The origin of homeostasis in the early earth. Journal of Molecular Evolution 31:257-64 Summary and Link to Full-Text.
  12. Davies P. The Fifth Miracle: The Search for the Origin and Meaning of Life (Paperback) Simon & Schuster ISBN-10: 068486309X ISBN-13: 978-0684863092
  13. Galimov EM. (2004) Phenomenon of life: between equilibrium and non-linearity. Orig.Life Evol Biosph. 34:599-613.
  14. 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
  15. Sayer RM. (2006) Self-organizing proto-replicators and the origin of life. Biosystems PMID 17014952
  16. 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 61:1809-1818 PMID 17008220
  17. Szathmary E. (2006) The origin of replicators and reproducers. Philos Trans R Soc Lond B Biol Sci 361:1761-1776 PMID 17008217
  18. Koonin EV. An RNA-making reactor for the origin of life. PNAS 2007;104:9105-6
  19. Baaske P, Weinert FM, Duhr S, Lemke KH, Russell MJ, Braun D. Extreme accumulation of nucleotides in simulated hydrothermal pore systems. PNAS 2007;104:9346-51.

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