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.]
Excellent post. I applaud you for your pithy comments.
In the meanwhile I'll keep him in my thoughts
I will pray that Iran's current coup attempt bears fruit so that our troops will no longer have to worry about that front. Thanks for your thoughts for my son. Prayers up for the 10th Mountain.
I did answer it. I asked why does the fossil record show a lack of modern species the farther back you go yet show numerous other species that do not exist today. Macro Evolution explains it very well, Creationism and ID doesn't.
But you know what SoldierDad, I really do give up this argument. I concede. You win. Sure... Creationism... who needs proof. Teach the controversy... Let's teach Noah's flood made the Grand Canyon. Can I prove it didn't? No... so go ahead... teach what you want.
It's midnight here and I am unusually tired, good night.
You post these controversial articles that YOU KNOW will get Freepers at each other's throats...and then you cutely say "Everybody be nice".
What a trouble maker!
What a trouble maker!
The title of the article was Genetic evidence for punctuated equilibrium.
It is an article about science, and some recent discoveries.
Are you suggesting that this is not an appropriate topic for an FR post?
Where is the controversy? Is there some scientific argument against this article?
Or, are you suggesting that this article may be opposed by a few religious fundamentalists, and therefore is not appropriate for FR?
Could you please clarify your opposition to this, and other scientific articles?
I hope you rest well. I know you believe you are giving the answer I'm looking for, and I appreciate what you've provided. I must admit that of all those who have made posts to me, you are the only one who has provided a complete explanation that makes sense.
I do not accept "creationism" as expressed by some. I think there could be an alternate explanation for why the fossil record shows a lack of modern species the farther back that record goes, but there can be no proof for that explanation. And, this isn't about me. I neither can win or lose, which is true for all others as well. Just asking questions - looking for explanatations which make sense. Thanks for your well thought out posts. Gives much food for thought.
You see what I mean?
I didn't offer A SINGLE opinion on the article and ALREADY I got poster challenging me on WHY I OPPOSE it. LOL!
No, it wasn't. It was a load of ignorant crap.
Don't hold your breath waiting for an answer.
It was scientific skepticism that lead me to the right.
No, it doesn't.
I think "punctuated equilibrium" sounds as silly as the idea that the Earth's ecosphere is periods of stability followed by periods of great upheaval.
That is, not very silly and very likely. Or do you believe that the Earth changed at the same speed throughout it's existence?
placemarker
Thanks. Such a display of egotism is really disgusting!
The prophet Isaiah:
Woe to those who go down to Egypt for help,
who rely on horses,
who trust in the multitude of their chariots
and in the great strength of their horsemen,
but do not look to the Holy One of Israel,
or seek help from the LORD.
Yet he too is wise and can bring disaster;
he does not take back his words.
He will rise up against the house of the wicked,
against those who help evildoers.
But the Egyptians are men and not God;
their horses are flesh and not spirit.
When the LORD stretches out his hand,
he who helps will stumble,
he who is helped will fall;
both will perish together.
Isaiah 31:1-3
If I cared to do so...
I guess you failed to read my opening comment:
I disprove your points by bolding your words
You alone are responsible for the content and tone of your posts.
100
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