Skip to comments.Kibble for Thought: Dog diversity prompts new evolution theory
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 WisconsinMadison.
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.
Well I for one am a little dog hating, creationist Rebel. Anyone got a problem with that?
The existence of cats disproves the possibility of natural selection.
There's lots of them neo-confeds who think Abe Lincoln was a son of a bitch -- so I guess we've got that connection, too!
Different dog types are not different species. They are different RACES within the species. Two of any type dog mated together produces viable offspring that can reproduce. This is even applicable to wolves and dogs. I have read that the DNA of a wolf and chihuahua are virtually identical, proving that all dogs are really domesticated wolves.......
Pocking and hoping to shore up the inevitable.
Another failed theory which adds nothing. Mutation isn't evolution, since no improvements are seen. And they can't prove the diversity doesn't already exist in the dog gene's.
Bless your heart ... you have such a sense of humor ...
LOL. It is a known fact that Sherman tortured cute little puppies who had rapidly evolved long noses on his March thru Georgia. There. Something for everyone.
I have read that the DNA of a man and a monkey are virtually identical, proving that all men are really ...
> Mutation isn't evolution, since no improvements are seen.
Aren't you cute! Yes, I'm sure that wolves are just as good at going undergound into critter-tunnels as Dachshunds, and that bulldogs can track smells as well as bloodhounds. Yes, there are no advantages from one mutation to another...
Humans feed and take care of dogs.
The dog thinks the human is a god.
Humans feed and take care of cats.
The cat thinks ITSELF is a god.
Monkeys and humans cannot mate and produce viable offspring that can reproduce themselves.....
Been talking to my wife?
Dogs have Masters
Cats have Staff
I believe that they are selectively breeding humans with the servitude gene.