Posted on 07/18/2006 9:06:26 AM PDT by PatrickHenry
Thanks to their domestication and favored pet status, dogs have enjoyed a genetic variability known to few other species.
It may be time to revise that old maxim about humans and their canine companions. A man, it seems, is a dog's best friend, and not vice versa.
A paper in the June 29th issue of Genome Research presents evidence suggesting that the domestication of dogs by humans has given rise to the immense diversity of the canine species by allowing otherwise harmful genetic mutations to survive.
"Dogs that would have otherwise died in the wild would have survived because humans would have allowed them to," said Matt Webster, a geneticist at the University of Dublin and one of the study's authors.
The stunning diversity of dogs — Canis lupus familiaris, includes lumbering St. Bernards, sprightly Jack Russell terriers, and graceful greyhounds — has been a source of scientific interest since Darwin, who speculated that these creatures must have descended from several different species. (Scientists now know dogs have a single ancestral species, the gray wolf.)
"Within a single species you have this tremendous range of morphological variation, all this diversity — head shape, body shape, coat color, length — and a tremendous amount of variation in behavior," said Leonid Kruglyak, a geneticist at Princeton University. "Where does all this come from? The parent species, which is the wolf, doesn't show this diversity."
Webster and his colleagues collected and sequenced DNA from the mitochondria of wolf and dog cells. Using this data, they looked for genetic mutations and calculated the rate at which mutations appeared.
Genetic mutations can be divided into two broad categories: nonsynonymous mutations actually change the protein that a stretch of DNA codes for, while synonymous, or silent, mutations do not.
Webster and his colleagues found that the silent mutations occur at similar rates in dogs and wolves, but that nonsynonymous mutations accumulate twice as fast in dogs as they do in wolves. These random changes to proteins are usually harmful, and would have a weakly deleterious effect on dogs and their ability to survive, said Webster.
"That suggests that during dog evolution there's been a relaxation of selective constraint," he said. "These additional changes that have happened during dog evolution have escaped the pressure of natural selection."
Because humans made it easier for domesticated dogs to survive, random genetic mutations that reduced evolutionary fitness — and would have died out in wild dog populations — were able to persist. Furthermore, as humans bred dogs for more desirable traits, they may have exploited these random mutations, accentuating already present variation.
"A lot of the changes over dog evolution would have provided the raw material that humans have used to shape different breeds," Webster said.
The result, then, is the phenomenal diversity in characteristics among different dogs and dog breeds today.
Elaine Ostrander, a geneticist at the National Human Genome Research Institute who worked on the institute's dog genome project, praised Webster's research and its use of mitochondrial DNA.
"For them to focus on mitochondrial DNA was an insightful decision," Ostrander said. "It's been neglected in canine genetics."
Mitochondrial DNA, because it resides outside the cell nucleus, is passed down only from mother to offspring, and it accrues mutations particularly fast. While that might make mitochondrial DNA a natural place to study rates of genetic variation, it's not yet clear whether Webster's findings will apply to the nuclear genome.
"The mitochondrial genome is such a small percentage of the dog genome," said Princeton's Kruglyak. "The interpretations are somewhat speculative."
Nevertheless, he conceded that the researchers' findings and proposed explanation are reasonable, even if not definitive.
"It's difficult to figure out what exactly happened over the last 10,000 years of dog domestication," he said. "It's not clear that any other species has been pushed by artificial human selection to the same extent. There's definitely a very interesting set of questions to be answered."
Details, details.
Since Chihuahua's come from Mexico, I'd say it is probably the chupacabra.
Humans have successfully manipulated dogs' genetics until the dogs have us just where they want us.
Chihuahua's don't forget, they are just on a shorter schedule than bigger dogs. Also those tiny tiny bladders might have something to do with it.
Socialism has an even bigger impact on human diversity. It broadens the gene-pool, mostly in undesirable directions, while jail serves to fine tune it. War's role in human evolution is as a big reset button, bringing the gene pool back into a very narrow range. It's why humans are remarkably the same the world over, and why the Neanderthals no longer exist.
And then, sometimes, there doesn't appear to be any variation at all ~ to wit, all kinds of insects on trees in the Amazon.
oxymoron alert.
What I said.
A petri dish can resolve that problem! Betcha' ya' get a big ol' yeller dawg out of it too.
There's another process where something gets "de-methylated" and genes thought to be dormant get expressed.
The genes don't change at all.
"And then, sometimes, there doesn't appear to be any variation at all ~ to wit, all kinds of insects on trees in the Amazon."
No variation??
I believe that in someways, man and dog co-evolved, together.
You can play with those foxes all day long and all you're gonna' get is a sexed out dog ~ with no pups.
That doesn't mean those dogs aren't trying to breed with you though.
No it isn't, the poster said "cutsy" not "crusty" ;0)
"I'm hoping -- perhaps in vain -- that everyone won't pile in to post cutsy pics of your dogs."
That, at least, would be better than what we usually get on any thread that mentions evolution.
(NOTE: that was an explanation for why there seemed to be entirely different, but otherwise identical in appearance critters on each and every large tree in the amazon ~ I suppose the researcher didn't get any more funding because he was unable to tie this into how serious human rendered habitat loss was going to be to diversity in the biosphere.)
"I have known dogs and cats to possess individual, unique personality traits and intelligence that are far beyond what the Bible calls voided minds of brute beasts."
That is somthing that has always bothered me since I was a kid. I personaly think every dog I've ever had, had a soul.
Each one had his own unique personality, and it always amazed me how they could communicate to get what they need, want, or to get you to play with them. Each one also had the knack to know when my wife or myself were upset, and they knew their affection would help make things just a little better. I think God put man and dogs together because he knew it would be a mutualy benificial relationship.
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