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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."
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Taken as a whole...it can be argued that unlike other non-human animals, that dogs are an extension of man, and the behavior of each altered the development of the other in profound symbiotic ways.
No cutsy pics, but you have to put up with my dachshund story. As the keeper of the dog food for 6 dachshunds of varying coats...smooth, long haired, wire...I can attest to their differences through genetics/breeding. Dachushunds were called badger dogs back in the eighteenth century, and pictured with basset hounds. Then dachshunds were bred with spaniels to achieve a longhaired coat, with change in temperament, too -- laid back, spaniel-like. Terriers were bred to dachshunds to get the wire coat and fiery terrier temperament. Really interesting, although my smooth male, supposedly tough, was nothing of the sort before being fixed. Once neutered, he turned into Mr. Hyde. All the testosterone went to the brain.
Interestingly, this article appears to say otherwise - in a sense. Dogs mutate about twice as often as wolves.
The behavior of animals alter the development of one another in profound symbiotic ways throughout the animal kingdom. Actually, the same goes for the other taxonomic kingdoms as well.
The damage the AKC has done to the German Shephard is a crime. The back legs are so short it looks like they are on training wheels (Americans like an angular back).
If you see German Shephards from German and compare them to the American version you can see the difference.
Because they wanted them to bark (which wolves rarely do) and wake them up when danger approaches.
PS. The only real difference between human behavior in this sphere is the premeditation, but human intelligence is natural as well.
I didn't know the moon was dangerous.
I mean difference between humans and the rest of the animal kingdom, of course.
It's a very good answer. Do some research. The bugs didn't change their genome ~ the bacteria and fungi created a "physical separation", just like the one proposed for specieation among the dinosars ~ drifting continents, et al.
True enough. My friend has a husky that tries to hump everybody (a female dog, strangly). With a dog of that size, it's more "hip-humping" than "leg-humping".
That's an invitation to Helen Thomas pics.
Sorry - you must have misread. The post said "cutsy" - not "horrific".
Obviously, animal of x size with z length fangs and z running speed will affect both possible prey and predators, and even competitors...but generally not to near the extent of humans and dogs. There is substantial evidence that humans and dogs are generally born with some level of innate understanding of how to communicate with each other.
LOL
Without getting into the varying definitions of natural, and using what I think is yours...I don't think I implied otherwise.
"It's a very good answer. Do some research. The bugs didn't change their genome"
Sure they do. Every generation in fact.
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