Origin of Life

From: Arthur V. Chadwick (chadwicka@swau.edu)
Date: Fri Jan 14 2000 - 11:48:28 EST

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     From Carl Woese: Proc. Natl. Acad. Sci. USA Vol. 95, pp. 6854ö 6859,
    June 1998

    A concept of the universal ancestor turns on more than phylogenetic trees,
    however. The Archaea and Bacteria share large number of metabolic genes
    that are not found in eukaryotes (18, 20). If these two ÎÎ prokaryoticââ
    groups span the primary phylogenetic divide and their genes are vertically
    (genealogically) inherited, then the universal ancestor must have had all
    of these genes, these many functions: This distribution of genes would make
    the ancestor a prototroph with a complete tricarboxylic acid cycle,
    polysaccharide me-tabolism, both sulfur oxidation and reduction, and
    nitrogen fixation; it was motile by means of flagella; it had a regulated
    cell cycle, and more. This is not the simple ancestor, limited in metabolic
    capabilities, that biologists originally intuited. That ancestor can
    explain neither this broad distribution of diverse metabolic functions nor
    the early origin of autotrophy implied by this distribution. The ancestor
    that this broad spread of metabolic genes demands is totipotent (21), a
    genetically rich and complex entity, as rich and complex as any modern
    cell÷ seemingly more so.
    Yet the totipotent ancestor also fails: it cannot explain the manner of the
    ancestorâs evolution, i.e., how it became so miraculously complex in so
    short a time and just as rapidly gave rise to the ancestors of the three
    primary lines of descent. All of this apparently happened in far less than
    1 billion years, whereas evolution within each of the three primary lines
    of descent has been going on for over 3 billion years now with outcomes
    that donât even begin to compare with the spectac-ular ones associated with
    the ancestor and its original offspring (4)÷ yet experience teaches that
    complex, integrated struc-tures change more slowly than do simple ones.
    Moreover, the totipotent ancestor associates physiologies that have not
    been observed together in any modern lineage and asks that all ofthis come
    about through vertical inheritance. Thus, we are left with no consistent
    and satisfactory picture of the universal ancestor. It is time to question
    underlying assumptions.


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