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Forwarded by request.
philidor11 wrote... >Given the correct numbers, the calculator will produce the correct answer. >There is only one possible mechanism for addition. But the point is that the "calulator" in a cladistic analysis NEVER gets exactly the right numbers. To answer your question another way, I think that if the programmer could recognize every reversal and convergent trait in the fossil record, the analysis could theoretically be coded in enough detail to perfectly duplicate evolution. The algorithm could do it if the programmer knew what to feed it. The problem is that we CAN'T recognize all the homoplasy, and so we can't see the fine details in such characters that would enable us to code them separately. Both you and Tracy have argued that that tweaking the data is wrong because it prevents the analysis from objectively evaluating all the data. My response to this is that, because no analysis can produce perfectly objective results since the "objective" data entered in is almost always going to always be confused by homoplasy, using tweaking to try to get around homoplasy isn't really hurting anything. To put it another way, you might say that tweaking is trying to make the analysis MORE objective by removing homolasy biases. However, its important to keep in mind that we can never be 100% sure that the characters we have dropped are really dropped to homoplasy any more then we can be sure of any result produced by the analysis. Tweaking is a way of looking for clues. Its not going to produce definitve results any more then an analysis with all the characters. >Could I paraphrase this to say that because the cladistic diagram can be >used to explicate the results of your analysis, it can be adapted to show >your conclusion in a manner immediately apprehended by the people you are >explaining it to? Mmmmm...I don't think that is exactly what I meant. The point in tweaking an analysis isn't just to make the cladogram and the results of the analysis easier to understand. Its more to offer possible explanations for why parts of the overall analysis including all of the characters MIGHT be unresolved (if you suspect polytomies might be due to homoplasy), or even just to check a better resolved tree if you suspect homoplasy is involved. If anything, tweaking complicates the big picture, because it doesn't involve just stopping with the comprehensive tree and saying "well, we have so low resolution here, but maybee we'll sort it out someday". It carries the analysis further by experimenting with alternatives. LNJ ***************************************************************** It is our duty to make the best of our misfortunes and not to suffer passion to interfere withour interest and the public good. -George Washington It is your business when the wall next door catches fire. -Horace ***************************************************************** Jeffrey W. Martz Graduate student, Department of Geosciences, Texas Tech University 3002 4th St., Apt. C26 Lubbock, TX 79415 http://illustrations.homestead.com/Illustration.html |