He kills birds, mice and even this headless rabbit. He brings them into the house through the dog-door as gifts...I suppose, in exchange for the cat food we give him.
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."
Noooooo! :D
Just, An personal crusade to prevent clutter (Helen Thomases' Photos, thus saving bandwidth) on FR. :^)
Cool. Thanks.
I hope you find the guy your looking for.
Its' 2047 and no Helens. :D
Yeah. How on earth can they jump up on a windowsill, like a normal cat? Those little dumpy legs are just creepy.
Ok, now you have done it...posted a pic of my favorite dog in the world, the basset hound...I have been owned by 3 of them, and loved every minute of it...thanks...
I've been "owned" by my first Basset for the past six years. I fear I will never be able to live without a Basset underfoot again. I wuv my "Rufus the Doofus!"
I actually won him in a poker game, believe it or not. He was going to be listed for sale in the paper later that week, anyway. My brother won his German Wirehaired that way, too.
(Please don't report us to PETA, LOL!)
The flip side of that is child rearing. A tribe that has grandmothers has an advantage over a tribe that does not -- in part because of their wisdom, and in part because having grandmothers to care for older children frees up the younger women to have more babies.
Samurai crabs, maybe?
Look at what's going on down in Brazil with these boys.
That idea makes a lot of sense.
Then explain why there's more than one species of Ants?
To quote E.O. Wilson
"Human generals might do well to study ants, arguably the most warlike and aggressive creatures on the planet. Ant colonies ambush, kidnap, rob, and raid other ants. There are even "suicide bomber" ants that explode their own bodies in order to spray enemies with toxic secretions. If ants had nuclear weapons, they would probably end the world in a week."
"The same cannot be said for evolution, Oort clouds, or the Big Bang. All of which are accepted scientific principles despite the fact that they are actually religious/philisophical beliefs. They are not scientifically proveable.
Which part of evolution is unobservable?
The source of variation? - Mutations are observed to occur. The results of mutations have been observed. There is direct observed evidence linking mutations (including errors during meiosis) with morphological changes.
That morphological changes are given a direction by selection? - This very thread gives observable evidence that selection, whether natural or artificial, can direct those morphological changes.
That those directed morphological changes can fix in a population? - This has been observed in the wild with finches and moths (and many others) and in the lab with bacteria.
That these morphologic changes can cause speciation between two groups? - This too has been observed both in the wild and in the lab. (the TalkOrigins archives has a list)
That given enough time two species can vary to an increasing degree becoming member species of different genera? - This hasn't been observed in the lab but it has been observed in the wild through indirect observation. Events leave physical evidence that can be examined and from which conclusions can be drawn. The maize/corn lineage is just one example of change leaving physical evidence that has occurred within the recent past. The record of change is in the corn genome.
That given enough time two species can vary to an increasing degree becoming member species of different taxa higher than genus? - Changes in species leaves physical evidence. In the case of higher taxa differences, some of this physical evidence is in the fossil record, some in morphological similarities of extant species and the rest is in DNA.
These are all rather simplistic representations of the evidence for the SToE but give an idea of how Evolution is 'observable'. Direct observation is not necessary in science as long as there exists physical evidence that can be used to recreate a specific event (or the traces of said event. Think quantum physics)). In many other fields, direct observation is impossible, all we can observe are the physical 'tracks' and the end result. All else is deduced.
Much of science proceeds by breaking larger problems and processes into small more easily controlled bits 'n bites where the number of variables (controlled, dependent and independent) is reduced to a manageable level. In biological evolution, we can observe, test and derive predictions from all of the operative mechanisms. When the fossil record is examined in light of the (lab and wild) tested and verified mechanisms, predictions (a process at the heart of science testing) can be made of what, where, and when (strata range) related fossils should be found.
What we haven't observed, directly or indirectly, is a mechanism that would prevent the accumulation of incremental morphological changes resulting in 'macro-evolution'.
It seems possible that if given enough time some type of ant would eventually take over the world, and kill off all resource competitors. They may still get their turn. A war making disposition leads to developing intelligence far in excess of that needed to find food and shelter. Insects never get very big compared to other animals for some reason which may be the reason their brain size and cognitive function seems to have hit a biological road block. But that could change.
Exactly. Either some of our apologists for the Church of Evolution here on Free Republic struggle with analogies or they're too far gone to recognize themselves.
At any rate, thanks for chiming in.
Umm . . . no it can't. Why do you say that??
(Oh, and don't forget the sex chromosomes, 22 +1 possibly mismatched pair.)
Agree. I saw a person walking an American show lines German Shepherd down the street a few years ago and at first glimpse I thought the poor thing was crippled. Well, I guess it was.
He kills birds, mice and even this headless rabbit. He brings them into the house through the dog-door as gifts...I suppose, in exchange for the cat food we give him.
Perhaps I nipped them in the bud.
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