Posted on 02/24/2006 4:12:32 AM PST by PatrickHenry
Charles Darwin would undoubtedly be both pleased and chagrined.
The famous scientist would be pleased because a study published online this week provides the first clear evidence that natural selection, his favored mechanism of evolution, drives the process of species formation in a wide variety of plants and animals. But he would be chagrined because it has taken nearly 150 years to do so.
What Darwin did in his revolutionary treatise, “On the Origin of Species,” was to explain how much of the extraordinary variety of biological traits possessed by plants and animals arises from a single process, natural selection. Since then a large number of studies and observations have supported and extended his original work. However, linking natural selection to the origin of the 30 to 100 million different species estimated to inhabit the earth, has proven considerably more elusive.
In the last 20 years, studies of a number of specific species have demonstrated that natural selection can cause sub-populations to adapt to new environments in ways that reduce their ability to interbreed, an essential first step in the formation of a new species. However, biologists have not known whether these cases represent special exceptions or illustrate a general rule.
The new study – published online in the Proceedings of the National Academy of Sciences – provides empirical support for the proposition that natural selection is a general force behind the formation of new species by analyzing the relationship between natural selection and the ability to interbreed in hundreds of different organisms – ranging from plants through insects, fish, frogs and birds – and finding that the overall link between them is positive.
“This helps fill a big gap that has existed in evolutionary studies,” says Daniel Funk, assistant professor of biological sciences at Vanderbilt University. He authored the study with Patrik Nosil from Simon Fraser University in British Columbia and William J. Etges from the University of Arkansas. “We have known for some time that when species invade a new environment or ecological niche, a common result is the formation of a great diversity of new species. However, we haven’t really understood how or whether the process of adaptation generally drives this pattern of species diversification.”
The specific question that Funk and his colleagues set out to answer is whether there is a positive link between the degree of adaptation to different environments by closely related groups and the extent to which they can interbreed, what biologists call reproductive isolation.
Funk and his colleagues saw a way to address this question by extending a method pioneered by two scientists in a now classic study of species formation in fruit flies published in 1989. The original method measured the way in which reproductive isolation varies with time. It proved to be very powerful and a number of other researchers applied it to additional species. Funk and his colleagues realized that if they used the results of these studies and added an ecological dimension then they would have an approach capable of measuring the link between natural selection and reproductive isolation.
“We thought that the idea itself was important, that this is a really powerful approach to a very major question,” says Funk, “but we thought that there was no way in the world that we were actually going to get statistically significant results.”
The reason for his doubt was the incompleteness and lack of uniformity of ecological data. “There are all these species out there and so few of them are known in intimate detail, so any kind of ecological characterization, through no fault of ecologists, will be limited in accuracy and precision,” Funk says.
Nevertheless, the researchers decided to do the best they could with the information available. So they collected information from the published literature on three basic ecological variables: habitat, diet and size. Then they used this information to calculate the differences in ecological adaptation between the hundreds of pairs of related species in the original studies.
When they compared these differences in adaptation with the degree of reproductive isolation for each pair and then added them up, the researchers found that the overall association was positive with a surprisingly high level of confidence: The odds that the association is simply due to chance are only one in 250, substantially higher than the standard confidence level of one chance in 20 that scientists demand.
“The fact that the association is statistically significant despite the crudeness of our estimates suggests that the true biological association is very strong,” Funk says. “Darwin’s famous book was called ‘On the Origin of Species,’ but it was really about natural selection on traits rather than species formation. Since our study suggests that natural selection is a general cause of species formation, it seems that Darwin chose an appropriate title after all.”
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Very good, and that's just on an annual basis.
"So, how many species do they count?"
About 6. I'm assuming you mean how many real scientists count.
The FIRST clear evidence???
Gee, Wally. And all this time I thunk it was a done deal.
I only count 5 ~
Yes you should, Jenny, in the hope that someone will slip up and post something like 1720...
Cheers!
I like that!
Sub-populations? What is that? Groups of less than one?
I know. Just call it an "act of God."
What else could it be? Evolution itself is one big joke.
"What else could it be? Evolution itself is one big joke."
Maybe you weren't joking about subpopulations after all...
As far as I know salmon are the only critters to which this narrow a reading is ever applied.
Remember, the politics of salmon include the politics of "free flowing streams", people against dams in or near the Grand Canyon, clear cutting, old growth forests, the use of water from Klamath Lake, Port of Valdez, North Slope Oil and concerns over the deadly ick that comes with domestication of salmon.
It's a complex and lucrative enough bunch of issues that you can get a lot of otherwise reputable, intelligent biologists to lie on the witness stand in court or before regulatory agencies.
"Bureaucrats didn't write the act. This was done by the legislative branch."
I'm sure the legislators had some help. :)
Years ago we worked with one of our youngsters on a science fair project. The object was to see what might be needed in a closed environment to grow food.
Along the way we found an article about a lady researcher who'd decided to count the number of viruses in a bucket of seawater. She wondered if there were enough of them to serve as a food source for bacteria.
The numbers she saw were absolutely astounding ~ millions! I've never forgotten that.
More recently one of the major researchers into the mapping of the human genome has taken an around the world cruise. He takes samples of ocean surface water along the way. He also counts the viruses, but he also identifies them and checks to see what genes they have.
His counts are in the millions, and he now claims the discovery of more than 2 million new genes we didn't know about earlier.
Up until recently, the belief was that these viruses developed inside bacteria and other critters. Still, it doesn't matter where they come from ~ they are different. That researcher has proposed that an artifical lifeform be created into which we could plug the viruses (and their genes) to see what they do.
Now, with the discovery of mimivirus, maybe we have to reconsider where these viruses, and their genes, come from, what they represent, and how we can use them.
My own thoughts are that they are manufactured items of a very ancient age. We serve as little more than their assembly point.
Quantum mechanics doesn't predict when an excited atom will emit a photon. Is quantum mechanics a sloppy notion too? No, it's very useful even though it doesn't answer every question. Just like natural selection.
Hey, how come you didn't answer whether you think field, energy etc. are "mere mental constructs?"
I don't think that is true in general. Viral genomes are generally far more compact (e.g. no regulatory or junk DNA). Generally speaking that is.
Bacteria are different ~ they have rod-shaped chromosomes.
I don't think that's true either. Bacterial chromosomes are strings or loops. Small loops are called plasmids.
Then, all at once, there was an infusion of new genes, and all hell broke loose ~ teeth, bones, talons, blood, etc., etc.
I assume we're speaking of the "Cambrian Explosion" here. IIRC, there is evidence that genetic diverence preceded the Cambrian by maybe a half billion years. Pre-Cambrian multi-cellular fossils have been found. One reason some of them were not previously detected is because they are so unexpectedly small.
But relatively sudden appearance of so much novelty is certainly unexplained. I take it you think the earth was inundated by viruses from space bearing genes and systems of genes for teeth and bones etc. etc. Well, that certainly seems implausible, but tell me, how will we test your theory?
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