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.]
I have no desire to try to persuade you to believe in biological science if do not wish to, but your statement is wildly inaccurate.
The theory of evolution does not state that humans "started off as a monkey". The evidence shows that humans share a common ancestor with apes, dating back about 8 million years ago.
Hope that helps.
Prime placemarker
"human started off as" - "humans share a common ancestor with"
Parsing words.
No sir, there is a very, very big difference between the two.
Consider it this way--you and your cousin 100 times removed both have a common ancestor at some point in your family history. You both descended from an ancestor, say, 1000 years ago. Simply because you share this common ancestor, however, does not imply that you "started off as" your cousin.
For the same reason you wouldn't consider your distant cousin an "ancestor", it is inaccurate to state that we "started off as" apes (or, as you put it, monkeys).
Okay, "came from". Is this more accurate.
No, it isn't. You didn't "come from" your distant cousin, did you?
The analogy of the "distant cousin" isn't remotely accurate in this dialogue. Distinctly different branches of the family tree. If humans "decended" from some ape like creature, then we had to have an original ancestor from which we sprang. It isn't possible for someone to "come from" a cousin, so that analogy doesn't wash.
That is exactly my point. Your original statement that evolution is the "belief that modern human started off as a monkey" is wrong for precisely that reason.
Apes (and more distantly, monkeys) are our evolutionary *cousins*, not our ancestors. That is a very important distinction that your statement mischarcterized.
"Mischarcterizing" something is a lot like "mischaracterizing" it.
I have cousins. Lots of them. If we trace our common ancestry we find that there is one source from which we all sprang on either our maternal or paternal sides. So, if humans are evolutionary "cousins" with apes, then there is "one" source from which we "sprang". Thus, the TOE postulates that we are decended from an ape (which means we came from . . .). Parse away.
Sorry, it's disqualified.
It's 200.
But, this is precisely what some who advocate the "truth" of ToE are claiming. Carry out the "cousin" analogy logically. My cousin and I are the offspring of parents related to one another (brothers or sisters) who are the offspring of two parents (using an intact family tree). Thus, while we are cousins, we come from a common "ancestor" If we are "cousins" to apes (monkey was just a general term, not literal), then there has to be a "common ancestor" from which we both sprang. We cannot be related to the ape without a common "ancestor" from which we branched from. Thus, as I decended from the ancestors of my grandparents, humans and apes must have "decended" from the ancestors which came before according to ToE. If those ancestors were not ape like, then I've been misinformed by those postulating the ToE. There is no other way that the ToE can be explained as it is being currently taught. Common Descent is the idea that humans and apes come from once source; thus the idea that we "descended" from ape like animals.
If humans come from monkeys, why are monkeys still around?
I don't think you're understanding the gist of our disagreement. The fact that the theory of evolution states that humans and monkeys and apes shared a common ancestor is not at issue.
What is at issue is your belief that the theory of evolution states that humans "came from" monkeys (or apes). You've since modified that position to "ape like" which is substantially closer to the truth.
The scientific theory of evolution states that humans and monkeys and apes all descended from a common ancestor. That you clearly understand a agree with. You continue to maintain, however, that if B and C both descended from A, it is accurate to state that B came from C. It is logically flawed, and does not accurately state the scientific theory.
Because humans didn't evolve from monkeys, that's why.
Read more. Seriously.
I really do not understand where you come up with "B" came from "C" as part of my comments. Nowhere have I made such claim. On the contrary, I've stated that the ToE postulates that "B" and "C" came from "A", nothing more.
Using the terms "monkey" or "ape" was nothing more than a parsimonious discriptor and not meant in it's literal transformation.
While I understand the tenents of ToE, that doesn't mean that I agree with all the claims of ToE.
That imprecise (and very inaccurate) use of terms is what I'm taking issue with. Your original statement that the theory of evolution is a "belief that modern human started off as a monkey, and then evolved into what we are today" is fundamentally flawed and badly misstates the truth.
Your parenthetical "if nature decided that modern man was superior to the monkey, then why are there still monkeys?" suggests to me that you misunderstand the basic nature of evolutionary ancestry.
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