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.
You don't have to convince me. Hell, even the French Poodle can breed with the German Shephard. You get bull fascists with their paws up.
If you want to call following some guy who was put to death on a cross "political power" that's your prerogative. To me it looks like sheer weakness. But then, I tend to look at the evidence differently than you.
Four men were bragging about how smart their dogs were.
One man was an engineer, the second man was an accountant,
the third man was a chemist, and the fourth was a
government worker.
To show off, the engineer called to his dog. "T-square,
do your stuff." T-square trotted over to a desk, took out
some paper and a pen, and promptly drew a circle, a
square, and a triangle.
Everyone agreed that that was pretty smart.
The accountant said that his dog could do better. He
called to his dog and said, "Spreadsheet, do your stuff."
Spreadsheet went out into the kitchen and returned with a
dozen cookies. He divided them into four equal piles of
three cookies each.
Everyone agreed that that was good.
The chemist said that his dog could do better still. He
called to his dog and said, "Measure, do your stuff."
Measure got up, walked over to the fridge, took out a
quart of milk, got a ten-ounce glass from the cupboard,
and poured exactly eight ounces without spilling a drop.
Everyone agreed that that was pretty impressive.
Then the three men turned to the government worker and
said, "What can your dog do?"
The government worker called to his dog and said, "Coffee
Break, do your stuff." Coffee Break jumped to his feet,
ate the cookies, drank the milk, claimed he had injured
his back while doing so, filed a grievance report for
unsafe working conditions, put in for workers'
compensation, and went home for the rest of the day on
sick leave.
They all agreed that that was brilliant!
> What scientist do, ideally, is intelligent manipulation of pre-existing materials.
Yes. Sometimes it takes intelligence to create an experiment that reflects a natural setting. But the fact that intelligence is required to create a nature-replicating experiment does not in the slightest imply that intelligence is required in the natural setting itself.
I know someone who is EXACTLY like that dog, and she IS a Government worker!......
Perhaps, perhaps not, but the fact that intelligence has been unable to produce matter, energy and the laws of physics ex nihilo or even offer a rational explanation of same does imply a unique being capable of such wondrous creation.
How do they know it's a "nature-replicating experiment"? Nobody was there to observe the conditions under which, in theory, viruses spontaneously generated from some non-living substance. Circular reasoning.
> does imply a unique being capable of such wondrous creation.
Does it? How?
Just because we don't understand something doesn't mean that there's some magic being behind it.
LOL. Keep telling yourself that, it will warm you on these cold winter nights.
I knew there was a reason I didn't trust the little rats.
Shalom.
> Nobody was there to observe the conditions...
Pre-biotic conditions on Earth cannot be known with certainty, but they can be known *generally* based on conditions foudn in the rest of the universe. Free oxygen, for example, is astonishingly rare. Somewhere around 95% of the visible mass of the universe is hydrogen; thus hydrogen dominates. Free oxygen very rapidly chemicaly bonds with hydrogen and forms water. Same with methane. And there are no known non-biological processes which will both produce and sustain an oxidizing atmosphere. If you were to kill off *all* life on Earth, Earth would have a carbon dioxide/nitrogen atmosphere relatively soon.
Looking at the rest of the universe, we can make a reasonable approximation of wha tthe pre-biotic atmosphere of the Earth was like. It it not "circular reasoning" to conclude that what holds true most places in the universe would also hold true on Earth. Consequently, a CO2/methane/nitrogen atmosphere on the early Earth is entirely reasonable and consistent with all available information.
When you bring a cat into your household, you become staff.
Shalom.
That's your best response?
Shalom.
My Chihuahua thinks she is a wolf!.........
If evidence points towards a creation event then that implies a Creator.
Your serve.
I thought creationists viewed speciation as an example of impossible "macro-evolution." If creationists are now calling speciation "mere micro-evolution," where are they drawing the macro-evolutionary boundry?
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