From welsberr Mon Oct 9 11:38:11 2000 Received: (from welsberr@localhost) by inia.cls.org (8.11.0/8.11.0) id e99GcBg25785; Mon, 9 Oct 2000 11:38:11 -0500 (CDT) Date: Mon, 9 Oct 2000 11:38:11 -0500 (CDT) From: "Wesley R. Elsberry" Message-Id: <200010091638.e99GcBg25785@inia.cls.org> To: dembski@discovery.org Subject: Information request re: Dawkins' "weasel" algorithm Cc: evolution@calvin.edu, welsberr 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