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."
I think you should quit while you are behind on this one. You obviously know nothing about ants. Try reading some before digging your hole deeper.
You obviously do not understand cats...
Your cat apparently believes you could not possibly survive without his assistance.. ( food contributions )
You are just a really big, helpless, adopted "kitten"...
Here's something I found interesting about Cro-Magnon at Wikipedia that supports my position. I'm not alone in my conclusions:
Analysis of the pathology of the skeletons shows that the humans of this time period led a physically tough life. In addition to infection, several of the individuals found at the shelter had fused vertebrae in their necks indicating traumatic injury, and the adult female found at the shelter had survived for some time with a skull fracture.
...
The Cro-Magnon likely came in contact with the Neanderthals, and is often credited to have caused or finalized the latter's extinction.
LOL...Can anyone really understand cats?
You seem to have an unsupported theory that you're touting as fact.
Cro-Magnon men and Neanderthals seem to have overlapped in their distribution, but there's no evidence they really had much to do with each other.
It's a supported theory. Fused vertebrae and skull fractures are evidence of intent to kill. Many human fossils show signs of skull damage and other trauma, and there are sometimes arrow or spear heads around. Modern humans come from a very violent and not so distant past. I think it's important to understand mankind's true nature. When schools teach natural selection, they should also teach the special case of high speed human evolution. The left embraces Darwin's ideas of natural selection but likes to pretend Darwin's Descent of Man book does not exist.
Past?
Modern humans live in a violent present.The incipient WW III brewing in the Middle East, the brutality in modern developed cities, and genocides in the third world all support the hypothesis that violence is our reality, not our history. We've just found more efficient means than clubs and spears.
The left embraces Darwin's ideas of natural selection but likes to pretend Darwin's Descent of Man book does not exist.
Scientists don't treat Darwin's work as the beginning and end of knowledge, because science marches on. Darwin's work is no more discredited than that of Hypocrates or Pythagoras or Copernicus or Euclid or Newton or Einstein. They're not refuted or discredited, but refined. We've built on their foundations and moved forward.
Cro-Magnons were perfectly capable of killing other Cro-Magnons without the Neanderthals' help, and that's probably what happened because Cro-Magnons would have had higher intraspecies competition than interspecies. This can't be considered evidence of Cro-Magnon/Neanderthal warfare unless such injuries are absent in Cro-Magnon remains from areas that Neanderthals did not inhabit, and they aren't. Your theory is unsupported.
Placemarker.
The poor dog's breeder TRIED to talk this first-time dog-owning couple out of an extremely energetic field dog . . . to no avail. And then they didn't give him anything to do . . . so he FOUND stuff to do, and drove them nuts.
I have Marley's twin sister. The story begins the same way -- I went to buy a couch-potato house dog and wound up with a high-energy field dog who chose US. The difference is that we went to Plan "B" and put her into training at 12 weeks, and found her lots of energy-burning activities to do.
She is now five, a model citizen, multi-titled in Agility and in Hunting Retriever. I can take her anywhere. But I didn't just wring my hands and watch her destroy stuff.
.....*Elvis's voice* Thank You, very much....*/Elvis's voice*
Who can say? There is insufficient evidence. Probably we had something to do with it, but more likely it was encroaching on their territory and competing for food rather than hunting them all down. Neanderthals were not very culturally advanced. They had only primitive tools, lived in small groups, and did not travel far. Humans had the technological edge. No doubt the climate change did cause problems for them, making it easier for Cro-magnon to move in and changing prey species ranges. It was probably a combination of multiple factors.
There are many species of monkeys, but that's not just a genus you're looking at, but a larger group. There are many organisms that are the sole species in their genus, that doesn't mean they killed all the other members off. Did the African and Asian elephants conspire to kill all other elephants?
Oh, and Occam's Razor is not as you have depicted it.
That's not a useful theory. It has too many assumptions, including ones that are not confidently even a factor. From Wikipedia:
Occam's razor states that the explanation of any phenomenon should make as few assumptions as possible, eliminating those that make no difference in the observable predictions of the explanatory hypothesis or theory.
Although insufficient evidence to convict in a court of law exists today that the Cro-Magnons killed off the Neanderthals, the warring tribe theory is more probable than just attributing the Neanderthals extinction to a fuzzy combination of factors. Are you uncomfortable with the idea that modern man is a war maker by nature, that our high intelligence and social abilities are the result of a violent war making past and present? Do you have an unrelated personal belief that is in conflict with this idea?
I hate it when the door's open, you sortof see them come in from outside out of the corner of your eye, but don't really look. Later, when they've been in for 30 minutes or so, you glance down and between your feet is the a$$ end of a rabbit, or squirrel, or bird, or field mouse.
Are you uncomfortable with the idea that modern man is a war maker by nature, that our high intelligence and social abilities are the result of a violent war making past and present? Do you have an unrelated personal belief that is in conflict with this idea?
I'm uncomfortable with baseless theories. There is no evidence that humans were responsible for the aggressive extermination of Neanderthals. From what we have seen of humans and extinction, the chief means is usually habitat destruction. It's more likely that humans encroached on Neanderthal territory and out-competed them for prey.
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Note: this topic is from 2007. |
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