From: Wesley R. Elsberry <welsberr@inia.cls.org>
>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.
It's been a while since I read TBW, but I'm almost certain you're wrong
here, Wesley. Dembski's description above of Dawkins' weasel algorithm seems
OK to me (except that I wouldn't call the weasel model an "evolutionary
algorithm", because it has a built-in target, and I don't think Dawkins
calls it one.)
Richard Wein (Tich)
--------------------------------
"Do the calculation. Take the numbers seriously. See if the underlying
probabilities really are small enough to yield design."
-- W. A. Dembski, who has never presented any calculation to back up his
claim to have detected Intelligent Design in life.
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