Posted on 12/21/2004 8:45:42 AM PST by PatrickHenry
The wide range of variety in domesticated dogs — from the petite Chihuahua to the monstrous mastiff — has powered a new view of what drives evolution.
Scientists have long known that the evolutionary changes that alter a species' appearance or create new species frequently occur in rapid bursts. One widely accepted theory holds that any evolutionary change results from a random switch of a single genetic unit within DNA.
These single-point mutations occur in about 1 out of every 100 million DNA sites each generation. This frequency is too low to cause rapid evolutionary change, assert John W. Fondon and Harold R. Garner, biochemists at the University of Texas Southwestern Medical Center at Dallas.
While examining human-genome data, Fondon found that small segments of repeated DNA sequences, called tandem repeat sequences, are frequently present in genes that control how an animal develops into its final appearance. Unlike single-point mutations, tandem repeat mutations occur when a cell's machinery for copying DNA makes a mistake and inserts a different number of sequence copies.
Such mistakes, which happen 100,000 times as often as single-point mutations, could alter an organism's appearance or function for successive generations.
"I was stunned by what I found," says Fondon. "It occurred to me that this might be a nifty way for [organisms] to evolve very rapidly."
To evaluate this hypothesis, Fondon and Garner looked for tandem repeat sequences in 92 breeds of domesticated dogs. For example, they examined a gene that determines nose length. They found that the number of times a particular sequence is repeated correlates strongly with whether a breed has a short or long muzzle.
Many researchers explain dog-breed diversity as the emergence of hidden traits in the genome. However, says Fondon, a more likely scenario is that genetic mutations occur in dogs at a high rate.
By comparing skulls of dogs over decades, Fondon and Garner found significant and swift changes in some breeds' appearances. For example, between the 1930s and today, purebred bull terriers developed longer, more down-turned noses.
Moreover, the researchers found more variation in tandem-sequence repeat lengths among dogs than they found in the DNA of wolves and coyotes.
These results suggest that dogs have experienced significantly higher rates of tandem repeat mutations than the related species have, says Fondon. Because tandem-repeat sequences litter the genes that control the developmental plan in many species, Fondon suggests that mutations in these regions could have a strong bearing on evolution.
"As a new finding about the biology and genetics of dogs, I'm all for it. But in terms of applying this to [evolution in general], I think there's a question mark," says Sean Carroll, an evolutionary geneticist at the University of Wisconsin–Madison.
Carroll notes that because dog owners have coddled their companions over the centuries, mutations that would have killed wild animals may have persisted in the gene pool of domestic dogs. Because domestication diverges from a standard model of evolution, he says, further experiments are necessary to add weight to Fondon and Garner's theory.
Pygmies and Zulus could still meet in the middle, so to speak.
The definition of "species" is not willingness.
My wife's little yippy dog mates with a soccer ball all day long. They ain't the same species (although I always have an urge to kick both).
The prerequisite is: "Can they mate without artificial help?" If so, go to next test. If not, then not the same species.
Ergo, little yippy dogs and really big dogs are no longer the same species.
My mutt is half border collie, half purebred miniature Lab.
Just about the harriest beast I ever met, I found one of his hairs on the floor and it measured 14 inches.
My neighbor insists my hound is smarter and more likeable than alot of people he meets. At 13, he's doing fine.
"Interesting, but terribly disturbing."
Yep.
WFT are you babbling about? While the origins and specifics of the Big Bang might be more than a little hazy, the evidence for it is pretty abundant (look up the work of Hubble). The evidence for evolution is even more abundant. We're now finding the genetic mechanisms that let it happen; we've understood the basic cause-and-effect principles of nature that drive it, and the fossils show the trail of it.
Wave your hands all you want. Rant all you want. Creationists will occupy the same hallowed ground as the hollow-earthers in the history books. If they persist, they will drag their religion down with them.
Some cats do behave strangely. I had a couple watch "Forever Amber" on the television a few years ago. I thought that was strange because the both hated the book.
When your fruit flies won't evolve, just call the one who notices "superstitious"...
Maaaan quit yippin'. Your theory has more holes than swiss cheese.
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The Five Crises in Evolutionary Theory, by Dr. Ray Bohlin
1. The unsubstantiation of a Darwinian mechanism of evolution
2. The total failure of origin of life studies to produce a workable model
3. The inability of evolutionary mechanism to explain the origin of complex adaptations
4. The bankruptcy of the blind watchmaker hypothesis
5. The biological evidence that the rule in nature is morphological stability over time and not constant change.
Raymond G. Bohlin is a graduate of the University of Illinois (B.S., zoology), North Texas State University (M.S., population genetics), and the University of Texas at Dallas (M.S., Ph.D., molecular biology)
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Joseph Boxhorn, author of the talk-origins 'FAQ' on Speciation, makes a bold promise from the outset in his choice of title for his paper: 'Observed Instances of Speciation.' Any rational person visiting this site will naturally expect to find a list of cases where scientists, under controlled experimental conditions, have actually observed the process of speciation taking place.
However, anyone expecting to find such a list in Boxhorn's 'FAQ' is due for a major disappointment. It is true that Boxhorn does list a number of scientific observations, yet -- almost incredibly -- not a single one of these observations can be described as 'speciation' in the Darwinian sense, except by employing the kind of Double-Think used by officials at George Orwell's Ministry of Truth.
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Proponents of evolution often attempt to discredit creation by pointing to occurrences of microevolution, such as speciation, adaptation, etc. To the evolutionist, microevolution is vindication for their belief in the much larger macroevolution. Their belief is that if these microevolutionary changes have enough time to accumulate, then eventually this will lead to a macroevolutionary change. And therefore, in their way of thinking, if microevolution is a well established fact, macroevolution must logically be an established fact as well.
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I think you should probably rethink your test with special consideration given to Pfizer.
One of my sons said he could breathe underwater, and the others thought he was evolving, but we concluded that he's really a space alien.
Does this mean Viagra has brought about a new human species? I mean, talk about your artificial help...
Sounds like it!
LOL. But, alas, not my test. It's in every Bio 101 text book.
And, with the horse answer above, in normal conditions, humans can normally mate without the help of little pills, so they are the same species, even if help is sometimes used.
If not, I would be of a different species than a democrat, as I would not consider mating with one without the help of tequila.
So...this has something to do with Typing Dogs......?
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