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."
Many things that are very forcefully put forth by science as existing have never been observed.
Like gravity. We've observed the effects of gravity, but no one has ever observed gravity. In fact, all we've done is postulated the existence of gravity.
Sure. Competition, in most modes, is an alternative to "war" with (or explicitly "killing off") another species, even though you tend to speak of war and competition as near synonyms.
Species typically compete with little or no agonistic interaction between them. They may not physically interacts at all and still be in competition for common environments or resources.
True, but that doesn't explain why there are many living species of monkeys, fish, birds, and only ONE species of humanoid still alive, only one version of a theme. Do you see how odd in nature that is? What could explain this other than Darwin's ideas in Descent of Man, that the inferior genetic or cultural tribes were killed off in warfare? These other humanoids were pretty smart, certainly smart enough to handle climate change and finding food. Disease may have done some of them in but it's rare that a disease alone wipes out a whole species. Though a seemingly forbidden idea in modern academia, the most obvious explanation is war.
I apologize. I guess at didn't communicate very effectively the fact that the basis upon which you were dismissing my analogy was entirely flawed. Let me attempt to explain.
1) As with the Oort cloud and macro-evolution examples, science does not require direct observation. In the case of Oort clouds, it doesn't even require any evidence.
2) While the dogs could observe the humans, this is a meaningless distinction with their human analogs as the dogs are not necessarily privy to the humans' intelligent design activities. If your distinction had meaning, I could point to a rock and say that it is more likely that the rock is an intelligent designer than it is that God is the creator simply by virtue of the fact that the rock can be seen.
3) Your point is irrelevent to the analogy as the analogy was not attempting to invalidate evolution or validate intelligent design. It was a commentary on the dynamics of the debate between evolution and intelligent design proponents.
4) While the analogy is flawed (as most if not all analogies are), the point was made regarding the nature of the debate between evolutionists and proponents of intelligent design. Therefore, the analogy served its purpose.
5) Based on the fact that you commented on a somewhat meaningless distinction between the analogy and the real life situation that the analogy represented instead of the point that the analogy was making, you apparently didn't understand what I was trying to say. Therefore, you are attempting to dismiss something whose meaning you don't get. That may or may not matter to you. I would contend that that's a problem for your objection.
However, we can directly observe the effects of gravity under controlled conditions. We can apply the scientific method to gravity to discover its principles and behavior.
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.
Too funny.
Wanna go to Lake Gaston next summer?
However, we can directly observe the effects of gravity under controlled conditions. We can apply the scientific method to gravity to discover its principles and behavior.
But you said...'Many things that are very forcefully put forth by science as existing have never been observed. They are simply and very stubbornly insisted upon because they are necessary to uphold the materialist view of origins.' I pointed out no one has ever observed gravity, just as an example. There are many, many others. You apparently agree that gravity has not been observed but exists. So you admit it is possible for things that have never been observed that are forcefully put forth by science as existing to exist. You've lost your credibility.
Doncha suspect that their inability to be housebroken is just God's way of punishing anyone who would own a chihuahua?
I pity you. Were you there? You have no proof. My granddaddy was no ape!!!!!!
You left out the Lake of Fire.
Could be. It's my mother in law's dog. Stupidist animal I ever saw allowed to run in the house.
Thanks, but my credibility is intact.
You should consider the conversation that you are breaking into and read the context before you jump in and embarrass yourself. I was not stating that things that could not be observed are not subject to scientific validation. The person I was responding to was saying that the inability to see something invalidated the analogy I was making. I was simply pointing out that the inability to observe something does not stop science from considering something. Some of those things are not valid, in my opinion. Like macro-evolution. Others, like gravitation, are completely verifiable. (Please note the fact that it is a mischaracterization to infer from the statement that you quoted that I was saying that all things that cannot be observed are put forth by science as existing and forcefully put forth because they are necessary to uphold the materialist view of origins. Perhaps my wording could have been more rigorous, but I honestly did not consider that someone was obtuse enough to assume that I meant that everything that was invisible was not verifiable. If you honestly thought that, then I stand corrected. That's patently ridiculous.)
Frankly, I see it going the other way. Geographic isolation and social taboos led to populations that are diverse, but fairly homogenous within each; more mobility and more acceptance of intermarriage have begun to blur the lines. Tiger Woods -- 1/4 white, 1/4 black, 1/2 Thai -- for example.
You can look at England, where Celts, Saxons and Normans have essentially ceased to be discernibly separate ethnic groups. Now, you're right that this mobility and mixing of populations will lead to greater diversity in terms of combinations of genetic traits that didn't combine before, but it won't be anywhere near as obvious as it is with dogs, and it won't happen in three generations.
The range of traits among domesticated dogs is the result of hundreds of different eugenics programs designed to select different traits depending on human needs; for the same phenomenon to take place with humans, you'd have to have someone selectively breeding dwarves with dwarves, 7' men with 7' women, athletes with athletes, physicists with physicists, etc.
Oops. Well, I'm new at this, lol!
You should consider the conversation that you are breaking into and read the context before you jump in and embarrass yourself.
I did, and the rest of your post refers, if to anything, posts made after my post to you. Any reader can go back through this and confirm this.
You credibility is further eroded.
This is a thread about evolution. I'm hoping -- perhaps in vain -- that everyone won't pile in to post cutsy pics of your dogs.
What would be the point otherwise?
"The analogy amounts to a strawman attack on the objections to intelligent design."
No, it doesn't. Unless calling someone an idiot amounts to an objection to intelligent design. What you have proved conclusively is that reading and understanding English is not your strong suit. You have succeeded in completely misinterpreting what I said in my original posts and my responses to you. (For example, I never said that you were making a claim as to the validity of evolution or intelligent design. I said that my analogy wasn't making any such claims.)
As this is Free Republic and not remedial English and I have less frustrating things to do than to try to endlessly explain what I meant when I said this and that, I believe I will refrain from commenting any further.
Thanks for your thoughts.
At this point, I can only conclude that you have me confused with someone else.
Sorry.
At this point, I can only conclude that you have me confused with someone else.
Nope. But I'll otherwise be gracious.
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