To: All Msg #23, Apr0393 11:02AM Subject: theories of abrupt appearance Recently, a 'theor

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From: Chris Colby To: All Msg #23, Apr-03-93 11:02AM Subject: theories of abrupt appearance Organization: animal -- coelomate -- deuterostome From: colby@bu-bio.bu.edu (Chris Colby) Message-ID: <113910@bu.edu> Newsgroups: talk.origins Recently, a 'theory of abrupt appearance' has been offered on talk.origins. I would like to make a few comments about it and ask a couple questions. To begin, I'd like to point out that theories of abrupt appearance are nothing new to biology. Prior to Pasteur, people thought 'lowly organisms' sprung into existence spontaneously. More recently, two theories of abrupt appearance have been written by evolutionary biologists. In the '40s, Goldschmidt posited that large phenotypic changes occurred by 'systemic mutations' -- i.e. large mutants, or 'hopeful monsters' were occasionally formed and very rarely they thrived. He saw the need to invoke this mechanism because he saw that in the organisms he studied (moths, I believe -- don't quote me), characters that varied between species were not the characters that varied within species. Although genes have been found that can produce large phenotypic effects (homeobox genes), his theory is almost completely discredited. (Although, I thought that some legit entomologists believe that the transition from 4 winged flies to 2 winged flies may have been via macromutation. The reverse occurs in _melanogaster_ (the ultrabithorax mutant).) Much more recently, Gould and Eldredge have authored punctuated equilibria (or 'punk eek' or much less charitably 'evolution by jerks'). This is another theory that states new species appear abruptly (at least in the fossil record). The gist of their theory is that transitions happen in isolated locales, then the newly speciated population may displace the old one. Instant transitions in the fossil record are the result of replacement by migration. (They also claim that phenotypic change may occur quickly (in geologic time) so that transitional forms are restricted both in space and time.) Both of these species address two specific topics, neither of which the 'theory of abrupt appearance' appears to: tempo and mode. Other posters have quickly picked up upon the lack of specificity in the theory with regard to time frame. I'll simply restate their question. How fast is abrupt? In Goldschmidt's theory 'abrupt' was within one generation. A hopeful monster was born and it could then begin increasing in population size if it happened to be well adapted (I'm not sure how it would find a mate -- the library has Goldschmidt, maybe I'll check it out if there is interest.) In punk eek abrupt transitions occur instantaneously in geologic time. But, these are artifacts of sampling. Unless the paleontologist is digging at the spot the population transformed, he/she won't find any transitional fossils. In most locales, the abrupt change in species is dues to species B (which evolved somewhere else) invading the territory of species A - _not_ species B evolving from species A. B may have evolved from an population of A, of course. Here's a brief cartoon to illustrate. Imagine the letters below are fossils; going down vertically would be older rocks. The horizontal is different geographic locations. B B B B B B B A B B B B A A A A B A A A A A A A A3 A A A A A A A A2 A A A A A A A A1 A A A A A A A A A A A A A A A B evolved from A in the leftmost column here; later it expanded its range at the expense of A. In all the middle columns, the A to B transition is due to migration, not evolution. The second question is mode. This is, I think, a much more important question to the most recent 'abrupt appearance' theory. In both the hopeful monster and punk eek theories -- new species came from old species. The question that is begging to be asked is -- where do species come from in the 'theory of abrupt appearance'? (And, of course, what evidence do you have for your proposed mechanism of species formation (whatever it is)?) Does Bird's theory answer these questions? (I suspect not.) Are there any predictions Bird's theory makes that are at odd with evolutionary biology? (Again, I suspect the 'theory' will prove to be squishy enough to accomodate any observation -- i.e. it won't really be a theory at all.) Chris Colby --- email: colby@bu-bio.bu.edu --- "'My boy,' he said, 'you are descended from a long line of determined, resourceful, microscopic tadpoles--champions every one.'" --Kurt Vonnegut from "Galapagos"

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