Origin of life: Difference between revisions
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[[Image:Oldest_carbon_life.jpg|thumb|right|A ball of carbon, found on Akilia island off Greenland holds the record as possibly the oldest evidence of life on Earth. The carbon ball, yielding an excess of carbon-12, the fingerprint of life, magnified 6900 times, is cradled in a cavity of a rock that dates 3.86 billion years old.]] | <!-- The following image was deleted because it was taken (and modified) from Nat'l Geo without permission. | ||
[[Image:Oldest_carbon_life.jpg|thumb|right|A ball of carbon, found on Akilia island off Greenland holds the record as possibly the oldest evidence of life on Earth. The carbon ball, yielding an excess of carbon-12, the fingerprint of life, magnified 6900 times, is cradled in a cavity of a rock that dates 3.86 billion years old.]] --> | |||
<blockquote>An early question that needs to be confronted, indeed a question that in the last analysis requires definition, is: What is life? Most biologists would agree that self-replication, genetic continuity, is a fundamental trait of the life process. Systems that generally would be deemed nonbiological can exhibit a sort of self-replication, however. Examples would be the growth of a crystal lattice or a propagating clay structure. Crystals and clays propagate, unquestionably, but life they are not. There is no locus of genetic continuity, no organism. Such systems do not evolve, do not change in genetic ways to meet new challenges. Consequently, the definition of life should include the capacity for evolution as well as self-replication. Indeed, the mechanism of evolution---natural selection---is a consequence of the necessarily competing drives for self-replication that are manifest in all organisms. The definition based on those processes, then, would be that life is any self-replicating, evolving system (Norman R Pace 2001).<ref>[http://www.pnas.org/cgi/content/full/98/3/805 The universal nature of biochemistry]</ref></blockquote> | <blockquote>An early question that needs to be confronted, indeed a question that in the last analysis requires definition, is: What is life? Most biologists would agree that self-replication, genetic continuity, is a fundamental trait of the life process. Systems that generally would be deemed nonbiological can exhibit a sort of self-replication, however. Examples would be the growth of a crystal lattice or a propagating clay structure. Crystals and clays propagate, unquestionably, but life they are not. There is no locus of genetic continuity, no organism. Such systems do not evolve, do not change in genetic ways to meet new challenges. Consequently, the definition of life should include the capacity for evolution as well as self-replication. Indeed, the mechanism of evolution---natural selection---is a consequence of the necessarily competing drives for self-replication that are manifest in all organisms. The definition based on those processes, then, would be that life is any self-replicating, evolving system (Norman R Pace 2001).<ref>[http://www.pnas.org/cgi/content/full/98/3/805 The universal nature of biochemistry]</ref></blockquote> | ||
Revision as of 10:10, 25 February 2007
An early question that needs to be confronted, indeed a question that in the last analysis requires definition, is: What is life? Most biologists would agree that self-replication, genetic continuity, is a fundamental trait of the life process. Systems that generally would be deemed nonbiological can exhibit a sort of self-replication, however. Examples would be the growth of a crystal lattice or a propagating clay structure. Crystals and clays propagate, unquestionably, but life they are not. There is no locus of genetic continuity, no organism. Such systems do not evolve, do not change in genetic ways to meet new challenges. Consequently, the definition of life should include the capacity for evolution as well as self-replication. Indeed, the mechanism of evolution---natural selection---is a consequence of the necessarily competing drives for self-replication that are manifest in all organisms. The definition based on those processes, then, would be that life is any self-replicating, evolving system (Norman R Pace 2001).[1]
The first replicators
Sources of energy
Community metabolism
Coding for amino acids
The RNA World
Rampant horizontal gene transfer hypothesis
Emergence of Darwinian struggle
Emergence of cells
Oldest fossils
References
Citations
Further reading
- Goldenfeld N Woese C (2007) Essays: Connections. Biology's next revolution The emerging picture of microbes as gene–swapping collectives demands a revision of such concepts as organism, species and evolution itself. Nature 445:369 (25 January 2007) doi:10.1038/445369a