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.
It doesn't? Gee, a lot of horse farms will be interested to know that their horses ain't horses.
Since you credit the Chinese story of inter-primate breeding, should I believe you when you define two breeds of dogs as two species?
Stop that, CG! I almost lost my lunch!
Right, the one with the fish playing baseball...floating there with bat in fin, looking out at the ball that is on dry land.
...Wild Monkeys!
There was no such fly, it was a lie...perhaps he'll die...
But it did get me thinking about the humble fruit fly and all that creature has contributed to the study of genetics without happening to "evolve" in the laboratory! The life cycle of a fruit fly is very brief, and scientists have been monkeying with them for *hundreds* of years in labs all over the world. You'd think, wouldn't you--that there'd be a new one by now, just by accident?
I don't happen to hold with ID--though it makes better sense than evolution. It's all a matter of time--and who controls the wheels of time.
Introducing the Stretch & Squish Theory of Evolution
How do you stretch an arm into a wing, or a fin into a leg? This sounds like the silly putty theory of evolution. An intelligent kid can purposefully make things out of silly putty, but the putty by itself is silly and has no goal in mind. Put the silly putty into a random machine of moving parts and chaos results.
Other problems quickly evolve from this theory. What if the top of the dog’s snout gets stretched by a tandem repeat mutation, but the bottom jaw does not? The dog can’t eat. What if the mutated dog can eat, but cannot find a mate with the same mutation? And don’t these guys know that dog breeding is not evolution, but intelligent design?
For these and other reasons, this Silly Putty theory of evolution gets Stupid Evolution Quote of the Week: their final sentence in the paper makes tandem repeats responsible for all the beauty and variety of living things:
How broadly this mode of evolutionary change is exploited [sic] in nature remains to be seen, but if the prevalence of repetitive elements within genes is any indicator, then mammals, insects, plants, and other genomes throughout the natural world may use this mechanism [sic] to achieve evolutionary agility.
“Evolutionary agility” – now there is an equivocation for the record books. How did a lizard learn to fly? By evolutionary agility. How did an ape learn to build spacecraft? By evolutionary agility. How did a dog learn to become a whale and dive deep into the ocean, navigating by sonar? By evolutionary agility. What an agile concept.
Papers like this diminish the prestige of the National Academy of Sciences. Peer review is supposed to prevent dumb ideas from getting published. If it were not for the desperation of the Darwin Party to keep sending new ideas up the flagpole to see if anyone salutes, they would have been forced to admit defeat long ago. This entry’s only value is in pointing out that the old neo-Darwinian theory of natural selection, acting on point mutations, is inadequate to account for the rapid change found in the fossil record. That is an admission that supports creation, not evolution.
Oh, dat is sweet. Flop-eared bunny.
"In vitro" is different from "in vivo" from "in the wild." (Seems the Romans were very civilized, no Latin for "in the wild.")
"It doesn't? Gee, a lot of horse farms will be interested to know that their horses ain't horses."
Don't be silly!
The distinction is, of course, that horses (with the possible exception of, say, Shetland ponies and Clysdales) can naturally breed, and would not have to rely on artificial reproduction, as would a Mastiff and a Taco Bell dog.
The scientific definition of a "species" is well known; it's not mine.
To take the issue to a less emotional topic than inter-primate breeding, Google "Liger" and see what you find.
Thanks!
Pomeranians were bred down from close to 30 pounds in Queen Victoria’s day to the present 6 or 7 pounds. Mine is a larger – weighing in at about 11 pounds – but he still thinks he’s a giant sled dog of the North as his ancestors were when they pulled sledges in Lapland.
He will take on any dog that offers a challenge, even taking out an adult Rottweiler several years ago – when he was much younger and it better shape.
Did you know that there are two kinds of horse-mule crosses? The most useful is when a donkey male meets horse female--but donkey females can carry the offspring of a horse male. The usual sure-footed and intelligent mule is the offspring of a horse female. The other kind is less useful, harder to manage.
That a Irish Wolhound male would produce a killing offspring in a toy poodle female--I don't doubt. But this is a matter of size, rather than breed.
You hate dogs ONLY because you haven't met mine yet. I tell people who hate fish that it is only because they have never caught a fish and eaten it the same day. Those store bought fish are old. Same thing with dogs, mine are so WONDERFUL you would change your mind and want one. ;9)
If you thought things through, you would see how patently ridiculous these assertions are. The evidence screams out against it.
Darwinism really has taken on the mentality of the Left.
While mules are sterile, they can be nominally male and female. The males are called "jacks", the females "jenny."
You can also cross other horse breeds--there have been known zebra-jackass crossings, a useless and misbegotton creature. All sterile.
Oh, I just hate little dogs. I love real dogs. I have a 6 month old rhodesian ridgeback - 45 pounds - on the way to 80-85 pounds. She is the greatest.
"In vitro" is different from "in vivo" from "in the wild." (Seems the Romans were very civilized, no Latin for "in the wild.")"
Doesn't matter, be in IVF or mere artificial insemination (in vivo) ---- any artificial joining necessary for breeding means that animals are not the same species, per the definition.
Now, this is not the ONLY distinction for two species, which is to what I presume you are alluding.
For example, lions and tigers (unarguably two distinct species of cat) sometimes mate in zoos --- resulting in a Liger --- with no artificial help, other than being locked up together.
But, I am keeping the issue simple and not talking about all the other factors that go into defining a "species" --- as natural reproduction is necessary to be the same species.
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