RE: Evolutionary rate

From: bivalve (bivalve@mail.davidson.alumlink.com)
Date: Tue May 13 2003 - 19:42:05 EDT

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    >The second is to do with ID and irreducible complexity. From what I gather, irreducible means that no component can be removed without the system as a whole failing. But what about components being added? Is it possible that what we see now as an irreducible system in fact became the way it is by loss of components from what was previously not an irreducible system?<

    This is a possibility, though probably very difficult to test. Evolutionarily, it would make sense for a complex, obviously reducible system to be streamlined over time, thus concealing the steps that went into its creation.

    A possible way of approaching this is to note that the fact that all pieces must be in place to achieve a particular function does not mean that the parts are useless in isolation. Thus, a system could be irreducibly complex in the sense that a whole lot of parts have to come together simultaneously to achieve the function, yet very readily assembled by cummulative individual events. For example, the citric acid cycle occurs as two separate processes in some bacteria. Putting the two together in the same part of the cell would complete the cycle, yet the cycle requires all the components. Another possible example comes from tRNAs. Modern organisms require about 21 amino acids, yet some of the basic tRNAs appear to be copies of others. This would suggest a time, prior to the emergence of any modern type of organism, when fewer amino acid types were in use. Gene duplication then enabled the development of a more complex system. However, it might also be possible for a !
     modified copy to replace an existing tRNA. This would necessarily have happened in the common ancestor of Archaea, Eubacteria, and Eukaryota.

        Dr. David Campbell
        Old Seashells
        University of Alabama
        Biodiversity & Systematics
        Dept. Biological Sciences
        Box 870345
        Tuscaloosa, AL 35487-0345 USA
        bivalve@mail.davidson.alumlink.com

    That is Uncle Joe, taken in the masonic regalia of a Grand Exalted Periwinkle of the Mystic Order of Whelks-P.G. Wodehouse, Romance at Droitgate Spa
                     



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