Posted on 10/07/2006 9:08:18 AM PDT by PatrickHenry
Evidence for punctuated equilibrium lies in the genetic sequences of many organisms, according to a study in this week's Science. Researchers report that about a third of reconstructed phylogenetic trees of animals, plants, and fungi reveal periods of rapid molecular evolution.
"We've never really known to what extent punctuated equilibrium is a general phenomenon in speciation," said Douglas Erwin of the National Museum of Natural History in Washington, D.C., who was not involved in the study. Since its introduction by Stephen Jay Gould and Niles Eldredge in the 1970s, the theory of punctuated equilibrium -- that evolution usually proceeds slowly but is punctuated by short bursts of rapid evolution associated with speciation -- has been extremely contentious among paleontologists and evolutionary biologists.
While most studies of punctuated equilibrium have come from analyses of the fossil record, Mark Pagel and his colleagues at the University of Reading, UK, instead examined phylogenetic trees generated from genetic sequences of closely related organisms.
Based on the number of speciation events and the nucleotide differences between species in each tree, the researchers used a statistical test to measure the amount of nucleotide divergence likely due to gradual evolution and the amount likely due to rapid changes around the time of speciation.
They found statistically significant evidence of punctuated evolution in 30% to 35% of the phylogenetic trees they examined. The remaining trees showed only evidence of gradual evolution.
Among the trees showing some evidence of punctuated equilibrium, the authors performed further tests to determine the size of the effect. They found that punctuated evolution could account for about 22% of nucleotide changes in the trees, leaving gradual evolution responsible for the other 78% of divergence between species.
Pagel and his colleagues were surprised that rapid evolution appears to contribute so much in some lineages, he said. "I would have maybe expected it to be half that much," he told The Scientist.
The researchers also found that rapid bursts of evolution appear to have occurred in many more plants and fungi than animals. Genetic alterations such as hybridization or changes in ploidy could allow rapid speciation, Pagel said, and these mechanisms are much more common in plants and fungi than in animals.
"Their result is pretty interesting, particularly the fact that they got so much more from plants and fungi than they did from animals, which I don't think most people would expect," Erwin told The Scientist.
However, it's possible that the analysis could be flawed, because the authors didn't take into account extinction rates in different phylogenetic trees when they determined the total number of speciation events, according to Douglas Futuyma of the State University of New York at Stony Brook, who was not involved in the study. But "they've got a very interesting case," he added. "I certainly think that this warrants more attention."
According to Pagel, the results suggest that other studies may have misdated some evolutionary events. Dates derived from molecular clocks assumed to have a slow, even tempo will place species divergences too far in the past, he said, since genetic change assumed to take place gradually may have happened very quickly.
"These kinds of events could really undo any notion of a molecular clock -- or at least one would have to be very careful about it," Futuyma told The Scientist.
Well known evolutionary mechanisms could account for rapid genetic change at speciation, Pagel said. Speciation often takes place when a population of organisms is isolated, which means that genetic drift in a small population or fast adaptation to a new niche could induce rapid evolutionary change.
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[Lots of links are in the original article, but not reproduced above.]
School Psychologist. What do you mean by "hammered"?
Students told over and over that this is the only way life on Earth can possibly have occured. What would qualify as an alternate cirriculum?
ID of course.
Fossils aren't rare at all. What is rare is for a particular, individual plant or animal to be fossilized.
There are fossils all over the place. I don't know where you live, but I have no doubt that I could take you to a place nearby that had fossils.
Fossils are common. What is uncommon is for a particular individual plant or animal to become fossilized. It takes a very specific set of circumstances. The reason there are so many fossils is the millions of years that plants and animals have lived on this planet. During that time, the circumstances that allowed fossilization have occurred again and again, leading to the rich fossil evidence we now have.
No contradiction.
But your non-answer has great relevance to the article that was posted.
That's a joke, right?
If the vast majority of living things that have ever existed on Earth did not become fossils, would you say then that you know little about most of the living things that have ever existed on Earth?
"So, fossils are rare = we have an extensive fossil record -seems contradictory to me."
That's because you put an = where you should have put an AND.
You have also modified the fact that fossilization rarely occurs to imply that there are few fossils.
And, if an example is still needed: one one in a thousand dead elephants get fossilized. If a million elepants die every year for a million years, how many fossil elephants are there?
Well, I thought maybe you were a member of "Evolutionists Against Evolution." Sorry if I was mistaken.
What was the final result? I only saw what it was when I voted.
"If the vast majority of living things that have ever existed on Earth did not become fossils, would you say then that you know little about most of the living things that have ever existed on Earth?"
Me, personally? Yes, I'd say that, but then, I'm not in that field, so I can't be expected to know a great deal about most of the living things that have ever existed on Earth.
However, it is amazing to see how many evolutionary series there are. While it's rare for a particular individual of any species to become fossilized, it's not all that uncommon for a few individuals of many species to be fossilized.
Every year, new members of the different series are discovered, as exploration continues. The progress in this, since the time of Darwin, is spectacular. And all that's done with very little money, compared to other scientific research.
Each new fossil species seem to fit right into the series that has grown from previous discoveries. Paleontologists learn more every year.
Me? I'm just an amateur and a reader of what is being discovered. I've collected fossils of some crinoid species, and have assembled a nice series of them, from several strata at the same site. Having done that, the progression in species over time is easily seen.
You don't believe that stuff, and that's just fine with me. I don't really care all that much what you believe or don't believe, since it doesn't affect my life in any real way.
Science thinks; religion believes.
Rough memory...a dispiriting 2:1 wrong way. :-(
Is Creationism science?
Belief gets in the way of learning.Robert A. Heinlein, Time Enough for Love, 1973
Is P.E. kind of like the "Immaculate Conception" of Evolution?
My only surprise is that the ratio wasn't bigger. I would have expected 3:1 or more. For a while I used to argue on the Crevo threads but now I really don't even bother. It would seem that those against evolution have it in their heads that their way is the right way and Science/Evidence be damned.
Same reason why non-scientific conjecture about evolution is allowed to be taught in schools.
". . . one in a thousand dead elephants get fossilized."
And this claim is based on . . .? What evidence? Conjecture yet again!
Another one for the trophy room...
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