Distal vs. proximate: Timing of design events and Pax-6

From: tikeda@sprintmail.com
Date: Wed Apr 25 2001 - 11:56:28 EDT

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    In "Re: Don't forget about me! (distal vs. proximate)",
    Bob repeated:

    [Berlinski and Dover quotes removed...]
    > I take these modular genes and Pax-6 fall in the design category
    > and indicate that design precedes application and is used in many
    > different applications. I don't see straightforward natural selection
    > in it, although natural processes are undoubtedly involved.

    I discussed this previously in:

    I conclude that there is no a priori reason provided to suppose
    that design events must have stopped or, at least, that we shouldn't
    consider the possibility that a designer could remain active.

    But back to the unrelated question about the evolution of eye
    regulatory genes: To be more specific, what part/s of Pax-6 do you
    think fall/s into the design category? The linear sequence? Its role
    in eye development? Its role in other developmental pathways?

    Pax-6 clearly appears as a variant of a class of transcriptional
    factors that predate the emergence of eyes. We know from experiments
    that transcriptional factors can get recruited into new roles in the
    regulation of genes for which there was previously no interaction. So
    the recruitment and/or diversification of the Pax-6 progenitor into a
    regulator of eye-spot development doesn't seem too much of a stretch to
    me. Certainly one would be hard pressed to claim that event required
    the direct intervention of a designer. Here's a web page I found on the
    evolution of the eye. It's not complete or terribly detailed, but at
    least it summarizes a little of the detail (Discussed by Berlinski?
    Are you kidding?):


    And what part of modular genes fall into the design category? When
    were the design events for these genes? Eukaryotes share many modular
    regulatory sequences with eubacteria and archeabacteria, which
    suggests that the design events must have preceded the split
    between the three kingdoms roughly 1-2 billion years ago (e.g. The
    two-component regulatory system initially discovered in bacteria is
    found in all three kingdoms).

    So what part of the evolutionary history is questionable? The origin
    of a particular module or its subsequent recruitment for alternate
    uses? If it's the origin of the modules which required design
    events, perhaps the examples of eye evolution aren't terribly
    helpful: the "modules" involved in eye development appear to have
    been present long before eyes came about.

    Again, I would strongly encourage anyone who is seriously interested
    in questions about the role and evolution of Pax-6 in cell development
    to look up the relevant, recent papers in Medline. Berlinski, for
    all his knowledge of the history of math, is definitely an uninformed
    hack when it comes to biology (as indicated by the quoted material).

    Tim Ikeda (tikeda@sprintmail.com)

    Mail2Web - Check your email from the web at
    http://www.mail2web.com/ .

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