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Old 02-21-2007, 03:49 AM   #16
a different tim
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Quote:
bryantee wrote
Just a quick brainstorm brought to my attention that punctuated equilibrium and gradualism can both occur. The main factor being the environment. If the environment changes requiring individuals to posses a certain trait, those without the trait will quickly die and those with will find their genes rapidly spreading through the population. Since the environment is always changing evolution will always be occurring, be it gradual or in quick spurts. But hey, that's based on no evidence - just a hypothesis I suppose. :P
I think PE was always supposed to be "rapid gradualism" although Gould flirted with saltation in the 80s. What you're saying is pretty much the Dawkins view - evolution is always happening, sometimes slowly, sometimes quickly. Gould argued otherwise - that long periods of stasis were punctuated by bursts of "normal" evolution. To Gould, these periods of stasis were something that needed explaining.

It's a bit tricky because in Gould the whole question is tied up with his views on selection - he wanted to show that species selection made sense, and that species were "Darwinian entities" that have "descendants". This only makes sense if you interpret the fossil record Gould's way - that between bursts of evolution that lead to speciation there is genuine stasis, and the normal sort of variation in a species is not the same thing as speciation. The Dawkins view makes sense if you argue that selection only takes place between individuals or (if you're being a strict Dawkins-ite) between genes.

This kind of "rapid gradualism" is however different from the saltationist view that I think the prof is giving in the quote that started this. If pharyngula answers Bacon I'd like to know what PZ thinks.

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Old 02-21-2007, 07:15 AM   #17
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So far nothing by PZ. A few people comment on the thread I posted though.
Here is a great video I just saw explaining evolution:
http://www.youtube.com/watch?v=qKb1L...otNickGisburne

The Atheist Jew asked about a Science Daily article. Straw man alert:

Jeffrey H. Schwartz, University of Pittsburgh professor of anthropology in the School of Arts and Sciences, is working to debunk a major tenet of Darwinian evolution. Schwartz believes that evolutionary changes occur suddenly as opposed to the Darwinian model of evolution, which is characterized by gradual and constant change.

The "Darwinian model" presupposes neither gradual nor constant change (what Dawkins derided as "constant speedism"). It does entail incremental change, where the increments are single applications of evolutionary operators in genetic space, not phenotype space. But some of those single increments can be seemingly large: see speciation by polyploidy.
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Re: Atheist Jew:


The title is a Fundies dream come true:
No Missing Link? Evolutionary Changes Occur Suddenly, Professor Says


That is almost exactly how creationists originally saw Punk-Eek. But Stephen Jay Gould turned out not to be their dream come true, despite Punk-Eek, Kurt Wise, and Rock of Ages.
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Old 02-21-2007, 09:18 AM   #18
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I'm at a loss why this is actually an arguement.

The determinant for evolution woulsd seem to be the rate occurrance of mutation along with the environmental pressures culling organisms prior to breeding.

While the former may be somewhat constant--and I'm postulating a somewhat here---the second may be static for a time and then incredibly stressful in short order.

If we see a relatively stable enironmental situation for a time we would see the build up of mutations some of which are beneficial others that are not but neitheer that may materially affect the continuaance of a species.

Come the comet or the drought or the volcano or the plague or the famine or what have you--the enviromental pressures select on a far more draconian level.

It occurs to me that if the pressures are so vicious as to completely eradicate any part of the species lacking a fundamental mutation in a single generation you could see the beginnings of speciation. Multiple generations and multiple cullings and you may see something as close toinstant speciation as exists.

(Like those ads for Lysol that kills 99% of household germs. Its the 1% that arer going to go on drinking lysol like beer, having a party and eventually rising up to kill us all.)

It is gradualism effected by catastrophe.

Unless I'm completely off base here.
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Old 02-21-2007, 09:29 AM   #19
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Well, this is the current model, but what the prof seems to be arguing for is saltation - i.e. large phenotypic change and even speciation in one generation - as opposed to the kind of high speed gradual evolution that you're talking about.

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Old 02-22-2007, 09:24 AM   #20
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Here is a better explanation of what Jeffrey Schwartz is thinking:

http://www.post-gazette.com/pg/06149/694046-85.stm
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Old 02-22-2007, 10:02 AM   #21
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Thanks, BEAJ.

OK, so he's talking about saltation due to hox gene type alterations. Genetically speaking, I should point out, it's still gradualistic.

His take on adaptation puzzles me. Adaptation is one of the best demionstrated things in biology, I think. The eye example is very strange because the precursors have been modelled and are well known. A sudden change in a developmental gene couldn't produce an eye from scratch anyway. Maybe he's been misquoted.

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