The Failures of Mathematical Anti-Evolutionism
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The Failures of Mathematical Anti-Evolutionism (Jason Rosenhouse) (z-lib.org)
The Legacy of the Wistar
Conference 4.1 again, does evolution have a math problem? Biology is less mathematical than other branches of the physical sciences, and this has sometimes been used as a cudgel against it. The argument goes like this: While we can all agree that dissecting animals and classifying them into groups is important work, it is hardly the same as predicting the mass of an electron to fourteen dec- imal places or to working out the motions of the planets centuries in advance. Evolution is biology’s premier theory, but it is not defended in the usual manner, is it? Real science uses equations to make precise predictions that are then verified by experiment. Evolution just points to a few fossils or anatomical comparisons and calls it a day. So goes the argument, at any rate. This attitude is far less prevalent today than it used to be. Physics is heavily mathematical because it studies simple, predictable objects like atoms and billiard balls. This makes it easy to capture their behavior in a few equations. Questions about complex, unpre- dictable, living things are less amenable to mathematical analysis. Mathematics is a useful tool for science, but it is silly to make mathematical precision the sole standard by which we evaluate a discipline. Still, it is an occupational hazard for biologists to be conde- scended to by more mathematically-inclined scientists. It happens periodically that some nonbiologist turns his attention to the myster- ies of life and, having thought about the problem for a few minutes, presumes to lecture biologists on how to do their jobs. Such people have seldom studied an actual animal, but they typically have some facility with symbol manipulation, and that is deemed sufficient to 84 4.1 again, does evolution have a math problem? 85 hold forth. The biologists, for their part, are expected to be grateful for this attention. This attitude was on full display at a 1966 symposium held at the Wistar Institute in Philadelphia. The proceedings were published the following year under the title Mathematical Challenges to the Neo-Darwinian Interpretation of Evolution . The proceedings make for interesting reading since they not only contain transcripts of the various presentations, but also transcripts of the ensuing discussions. The title is misleading because, of the seven main presenta- tions, only two posed challenges to evolution’s fundamental sound- ness. The first challenge came from Murray Eden, then an engineer at the Massachusetts Institute of Technology in the United States. The other was from Marcel-Paul Schützenberger, a mathematician then at the University of Paris in France. The other presentations had more to do with trying to formulate evolutionary questions in mathematical terms than they did with trying to refute the theory altogether. Eden and Schützenberger were both eminent in their own fields, which lent an air of gravitas to their arguments. When the local preacher claims to have a decisive argument against evolutionary theory, the challenge is easily ignored. But when the likes of Eden and Schützenberger have something to say, they get a full hearing. The symposium was chaired by Nobel laureate Peter Medawar. Among the presenters were Ernst Mayr and Richard Lewontin, both among the first tier of biologists of their time, and mathematician Stanislaw Ulam, who had been part of the famed Manhattan Project. The other attendees were likewise distinguished in their areas of expertise. In other words, there was some serious talent in the sym- posium’s audience, and all involved were taking the issues very seriously. Which made the actual presentations rather anti-climactic. For all of their eminence in their own fields, the anti-evolution arguments presented by Eden and Schützenberger were just bad, even given what was known back in 1966. That notwithstanding, they estab- lished the template followed by modern purveyors of mathematical 86 4 the legacy of the wistar conference anti-evolutionism. Digging into the minutiae of their claims will help us to understand the errors of their modern-day followers. 4.2 natural selection is like a truffle hog We begin with Eden’s presentation. He summarized his argument like this: Any principal criticism of current thoughts on evolutionary theory is directed to the strong use of the notion of “randomness” in selection. … The issue of plausibility is central to my argument; namely that when reasonable assumptions are made concerning certain natural processes, together with the assumption of certain specific kinds of randomness in the variation of heritable properties, then other phenomena which are empirically observable appear to be highly unlikely events. (Moorhead and Kaplan 1967, 5) His main argument in defense of this claim involves the prob- lem of finding functional proteins within the vast space of theoretical possibilities. A protein can be viewed as a long chain, each of whose links is one of twenty amino acids. If we imagine building a protein by randomly selecting two of these amino acids, then there are 20 ×20 = 400 possibilities. If instead we randomly selected three, there are 20 × 20 × 20 = 8,000 possibilities. Most proteins are much longer than this, so Eden asked everyone to imagine a chain with 250 links. We find that there are 20 250 possibilities, which is roughly 10 325 . That is a one followed by 325 zeroes. For a comparison, most people would consider a billion to be a big number, but that only has nine zeroes. We can say, therefore, that the space of all possible proteins is monstrously large. In contrast to this very large number, Eden put forth 10 52 as the number of proteins that could ever have existed in any organism in all of natural history. This number was based on a crude calculation, the details of which are not important. By itself, 10 52 is a large number, but it is very small compared to 10 325 . Somehow, the evolutionary 4.2 natural selection is like a truffle hog 87 process has found a tiny set of functional proteins within a vast space of possibilities. This needs to be explained, and Eden suggested two possible solutions: Either functionally useful proteins are very common in this space so that almost any polypeptide one is likely to find has a useful function to perform or else the topology appropriate to this protein space is an important feature of the exploration; that is, there exist certain strong regularities for finding useful paths through this space. (Moorhead and Kaplan 1967, 7) In the discussion after his presentation, Eden elaborated on this point: There is some path by which we have arrived at this relatively small corner in this large space, on the basis of a relatively small number of generations. What I am claiming is simply that without some constraint on the notion of random variation, in either the properties of the organism or the sequence of DNA, there is no Download 0.99 Mb. Do'stlaringiz bilan baham: |
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