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."
How do you measure genetic complexity?
One way is by counting the number of subsystems involved in the operation of the animal. In the case of humans, our brains have many more functions than is seen in other animals. Humans actually have two brains, an animal brain stem where among other things our feelings of pain and pleasure take place, and a highly evolved neocortex (new brain) where complex reasoning takes place.
Invalid response. 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.
How many people have ever seen the Oort cloud? Name them, please.
For that matter, who has observed one type of animal spontaneously evolving into a more complex type of animal for no other reason than a change in environment?
Pop science these days is filled all kinds of things that have never been observed. I would say that this once foundational aspect of the scientific method has all but been disposed of.
Normally one would blame it on the keyboard, but....
What is the basis for this statement? What's your measure of genetic complexity? Total quantity of DNA? Number of genes? Number of chromosomes? Humans are unexceptional, genetically, by all the criteria that I can think of.
Dolphins and chimpanzee brains have many more functions than is seen in other animals too.
The neocortex is characteristic of all mammals. Actually, the mammalian brain has more nearly six layers, not two. Once again, how do you measure complexity?
One more thing. Your original post spoke of genetic complexity. How do you measure genetic complexity?
Our brains have very exceptional genetics as evidenced by their exceptional complexity. That humans can live so long with a high metabolism is another indication of genetic complexity. The reason for our long lifespan, well past breeding years, is due to the advantages of having wise people around in war. If two tribes go to war, the side with more wisdom and life experience has a substantial advantage. Most human qualities can be traced back to their advantage in war.
One way is by counting the number of functional subsystems. For example algae do not have specialize reproductive organs while more complex plants do. Algae have fewer functional subsystems and are therefore less genetically complex. Does this need more explanation? I find it obvious.
You already made a false statement about humans having more subsystems.
My question, however, is not about complexity at the genetic level. How would you measure complexity of an unknown organism if all you had was the genome?
Each cell fights for survival.
All cells fight for the good of the whole.
If adaptation is needed, the cells adapt (mutate).
If not, they don't.
All creatures are the same. Made up of these cells. Each is intelligent, each has a will to survive.
You are made up of these creatures, these cells.
God gave them the intelligence and will to survive, the mutation is an environmentally induced product of the cells, the Eukaryotes.
God created. Everything after is evolution.
I'm not familiar with a Bible passage that uses that phrase... would you be so kind as to give me a reference quote? Thanks.
best,
ampu
I can only guess you're assuming, rather than actually reading, what Darwin says about war in Descent. I've just searched through the full text, and he doesn't give it anything like the central role you suggest.
Darwin includes war, and pestilence, as amongst factors mitigating against "ratio of increase" (rapid population growth) but in the same passage and others surrounding suggests that the inability to obtain means of subsistence (principally good food) is far more important.
Darwin mentions war several times in discussing man's moral sense and his identity as a social animal. For instance:
When two tribes of primeval man, living in the same country, came into competition, if (other circumstances being equal) the one tribe included a great number of courageous, sympathetic and faithful members, who were always ready to warn each other of danger, to aid and defend each other, this tribe would succeed better and conquer the other. Let it be borne in mind how all- important in the never-ceasing wars of savages, fidelity and courage must be. The advantage which disciplined soldiers have over undisciplined hordes follows chiefly from the confidence which each man feels in his comrades. Obedience, as Mr. Bagehot has well shewn (5. See a remarkable series of articles on 'Physics and Politics,' in the 'Fortnightly Review,' Nov. 1867; April 1, 1868; July 1, 1869, since separately published.), is of the highest value, for any form of government is better than none. Selfish and contentious people will not cohere, and without coherence nothing can be effected. A tribe rich in the above qualities would spread and be victorious over other tribes: but in the course of time it would, judging from all past history, be in its turn overcome by some other tribe still more highly endowed. Thus the social and moral qualities would tend slowly to advance and be diffused throughout the world.
IOW the one specific role Darwin moots for warfare is to INCREASE and improve human morality, sociality, cooperativeness and selflessness. (True enough, that's exactly the opposite from how leftists would tend to see the matter.)
I can find no place, however, anywhere in the entire text of Descent, where Darwin says anything at all like the thesis you attribute to him: That warfare makes men less variable.
Indeed Darwin says repeatedly that mankind is a HIGHLY VARIABLE species.
That's because we killed off in war all similar competitors long ago, the Neanderthals being the last.
Speculation at best. There is scant evidence, and nothing conclusive, that anatomically modern humans were ever in direct competition (let alone at war with) Neanderthals. It is, under the present evidence, at least a viable hypothesis that such competition had NOTHING to do with the demise of Neanderthals.
In earlier times the dogs were kept outside the village stockade.
The "advantage after a hurricane" is more likely. Not too long ago a tribe could hold a war and no one would come even if the invitations were sent out decades earlier. Just weren't enough people around.
BTW, I think dogs do realize we've influenced their evolution -- look at the chip on a Chihuahua's shoulder (he knows his ancestors were big, nasty brutes and he's pissed that he turned out the way he did).
Finally, I don't think dogs have the same concept of names that humans do. I think they mostly identify each other and us by our odor rather than some random combination of syllables.
Using current technology we couldn't. For now we still have to express the DNA into a living thing to observe what genetics are functional. Just measuring the amount and variability of the DNA strands isn't useful for determining genetic complexity.
I think its tied to the gene that makes them think they are bigger than all of the other dogs on the block (including us). "Hey big guy watch me, that's right I did it on your floor, now, what are *YOU* gonna do about it, HUH?!?"
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