Information request re: Dawkins' "weasel" algorithm

From: Wesley R. Elsberry (welsberr@inia.cls.org)
Date: Mon Oct 09 2000 - 12:38:11 EDT

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    Information request to William Dembski:

    [Quote]

    He starts with a target sequence taken from Shakespeares
    Hamlet, namely, METHINKS IT IS LIKE A WEASEL. If we tried to
    attain this sequence by pure chance (for example, by randomly
    shaking out scrabble pieces), the probability of getting it on
    the first try would be around 1 in 10^40, and correspondingly
    it would take on average about 10^40 tries to stand a better
    than even chance of getting it.12 Thus, if we depended on pure
    chance to attain this target sequence, we would in all
    likelihood be unsuccessful. As a problem for pure chance,
    attaining Dawkinss target sequence is an exercise in
    generating specified complexity, and it becomes clear that
    pure chance simply is not up to the task.

    But consider next Dawkins' reframing of the problem. In place
    of pure chance, he considers the following evolutionary
    algorithm: (1) Start with a randomly selected sequence of 28
    capital Roman letters and spaces (thats the length of METHINKS
    IT IS LIKE A WEASEL); (2) randomly alter all the letters and
    spaces in the current sequence that do not agree with the
    target sequence; (3) whenever an alteration happens to match a
    corresponding letter in the target sequence, leave it and
    randomly alter only those remaining letters that still differ
    from the target sequence. In very short order this algorithm
    converges to Dawkinss target sequence. In The Blind
    Watchmaker, Dawkins recounts a computer simulation of this
    algorithm that converges in 43 steps.13 In place of 10^40
    tries on average for pure chance to generate the target
    sequence, it now takes on average only 40 tries to generate it
    via an evolutionary algorithm.

    [End Quote - WA Dembski, "Can Evolutionary Algorithms Generate
    Specified Complexity", "Nature of Nature" conference, Baylor
    University]

    There are several issues that this text brings up. Of the three
    steps listed as comprising Dawkins' algorithm, only step (1) has
    anything like it in the pages of "The Blind Watchmaker". Steps
    (2) and (3) appear to be inventions rather than descriptions.
    What is the basis for claiming that steps (2) and (3) represent
    Dawkins' "weasel" algorithm?

    Further on, the issue of "tries" it takes to find a solution
    is raised. For "pure chance", a figure of ~10^40 "tries" is
    given, which would correspond to individual candidate
    solutions tested. For "weasel", though, only ~40 "tries" are
    given, but in this case the number 40 derives from the number
    of generations taken by the "weasel" algorithm rather than the
    number of candidate solutions examined. It seems to me that
    for the purpose of comparison, a "try" ought to mean the same
    thing for both approaches. I would like to see a restatement
    of the section concerning "tries" that takes this into
    account.

    Wesley

    cc: Calvin Reflector, evolution@calvin.edu



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