Kibble for Thought: Dog diversity prompts new evolution theory

Science News ^ | 18 December 2004 | Christen Brownlee

[PatrickHenry]

The wide range of variety in domesticated dogs — from the petite Chihuahua to the monstrous mastiff — has powered a new view of what drives evolution.

Scientists have long known that the evolutionary changes that alter a species' appearance or create new species frequently occur in rapid bursts. One widely accepted theory holds that any evolutionary change results from a random switch of a single genetic unit within DNA.

These single-point mutations occur in about 1 out of every 100 million DNA sites each generation. This frequency is too low to cause rapid evolutionary change, assert John W. Fondon and Harold R. Garner, biochemists at the University of Texas Southwestern Medical Center at Dallas.

While examining human-genome data, Fondon found that small segments of repeated DNA sequences, called tandem repeat sequences, are frequently present in genes that control how an animal develops into its final appearance. Unlike single-point mutations, tandem repeat mutations occur when a cell's machinery for copying DNA makes a mistake and inserts a different number of sequence copies.

Such mistakes, which happen 100,000 times as often as single-point mutations, could alter an organism's appearance or function for successive generations.

"I was stunned by what I found," says Fondon. "It occurred to me that this might be a nifty way for [organisms] to evolve very rapidly."

To evaluate this hypothesis, Fondon and Garner looked for tandem repeat sequences in 92 breeds of domesticated dogs. For example, they examined a gene that determines nose length. They found that the number of times a particular sequence is repeated correlates strongly with whether a breed has a short or long muzzle.

Many researchers explain dog-breed diversity as the emergence of hidden traits in the genome. However, says Fondon, a more likely scenario is that genetic mutations occur in dogs at a high rate.

By comparing skulls of dogs over decades, Fondon and Garner found significant and swift changes in some breeds' appearances. For example, between the 1930s and today, purebred bull terriers developed longer, more down-turned noses.

Moreover, the researchers found more variation in tandem-sequence repeat lengths among dogs than they found in the DNA of wolves and coyotes.

These results suggest that dogs have experienced significantly higher rates of tandem repeat mutations than the related species have, says Fondon. Because tandem-repeat sequences litter the genes that control the developmental plan in many species, Fondon suggests that mutations in these regions could have a strong bearing on evolution.

"As a new finding about the biology and genetics of dogs, I'm all for it. But in terms of applying this to [evolution in general], I think there's a question mark," says Sean Carroll, an evolutionary geneticist at the University of Wisconsin–Madison.

Carroll notes that because dog owners have coddled their companions over the centuries, mutations that would have killed wild animals may have persisted in the gene pool of domestic dogs. Because domestication diverges from a standard model of evolution, he says, further experiments are necessary to add weight to Fondon and Garner's theory.

[fr_freak]

Thanks for all the links. It will take a little while to get through them.

In the meantime, bear in mind that when I say we haven't observed evolution occurring, I mean we haven't witnessed one species arise from another. Fossil records may suggest that evolution occurred, but that's not what I'm talking about.

Let me make this clear: I do not deny that evidence for evolution exists. If it didn't, there would be no need for discussion, would there? However, I do not agree that the evidence is so overwhelming and airtight as to be indisputable, an assertion made by an earlier poster. So, sending me pages of links regarding fossils found somewhere that might be evidence of a horse ancestor, or a human ancestor, is not sufficient to say that evolution is an accepted fact.

[PatrickHenry]

... bear in mind that when I say we haven't observed evolution occurring, I mean we haven't witnessed one species arise from another. Fossil records may suggest that evolution occurred, but that's not what I'm talking about.

Yes. You're saying that we don't live long enough to personally witness much happening. This is true. But it's also true of continental drift, the formation of mountain ranges, the origin of this:

which could, after all, have been a Navaho public works project, and numerous other things in the world around us.

I assume you're not saying that you don't accept rational conclusions drawn from verifiable evidence. So mull it over. There's really overwhelming evidence of evolution. Lots of people aren't aware how much there really is, and how impossible it is to explain the totality of it in any other rational way.

[Conspiracy Guy]

LOL. Someone needs to fix it!

[Conspiracy Guy]

Ugggggggggggggggly aint it.

[grey_whiskers]

I was thinking of interstellar environments...

The lower T and P slow reactions way down.

See how easy it is to miscommunicate?

[orionblamblam]

> I was thinking of interstellar environments...

Not relevant to this discussion.

> See how easy it is to miscommunicate?

When one wants to, yes.

[grey_whiskers]

Have you ever heard of "ladder operators" in quantum mechanics, dudes?
"Let there be light" ;-)

and Jim Robinson begat Free Republic;
and Free Republic begat Crevo threads.

And there was heat AND light!

Or, for that matter, Path Integrals (thanks to the late Dick Feynmann for his classic text...)

[grey_whiskers]

Oh, yes, about your other post regarding tags, try the article / topic search in Free Republic and type in the words HTML sandbox.

Enjoy!

[grey_whiskers]

> See how easy it is to miscommunicate?

When one wants to, yes.

Wants to see, or wants to miscommunicate?
This thread has gotten cluttered up with mutant topics
(hat tip to Dave Barry) involving quantum mechanics,
meteor strikes, etc. as well as dog breeding and Rottweilers
having their nuts chomped.

In this environment, a disclaimer on your part regarding planetary vs. interstellar environments when regarding chemical reactions would have been welcome.

Additional condescension and rudeness is not sufficient recompense for your sloppy posting practices!

[MeanWestTexan]

No, it means (as the Talmud says, per LurkingLibertarian above) "all miracles happen in a natural way."

Here, the miracle of life as we know it happened per God's laws.

[MeanWestTexan]

I am using the definition I am reading right here out of a 15 year old college Biology book.

There ARE alternative definitions that are less precise, I agree. But those are not the definition used in classification of species.

[jwalsh07]

Very funny, did you read that piece?

[MeanWestTexan]

It is truly disturbing that they might create a "humanzee."

But (ignoring the whole evolution issue), humans and chimps have very similar DNA (the 99 or 98% figures you see are misleading, we're not quite as close as t).

In fact, humans and chimps are roughly as close DNA-wise than donkeys and horses and certainly "closer" than lions and tigers.

Hence, this abominable experiment is very possible, and, candidly, easy, for anyone with basic knowledge of animal husbandry.

So much for those using the loosy-goosy "potentially interbreeding" definition of species, huh?

[orionblamblam]

Yup. Says that while, in very conjectural theory, the universe *might* be a creation.... it also points out that the "creator" might well be no more than some government science project.

For *real* philosophical fun, imagine 400 years from now, a group of physicists using a ringworld-sized supercollider create a universe. That universe being the one they inhabit. Thus they are their own creators. No beginning, no ending. Whoopee.

Other lines in quantum mechanical thinking about cosmogenesis posit that "pocket universes" are formed naturally due to the space-time stresses caused by black holes. And that each time this happens, the laws and constants are changed ("mutated") very slightly. This would lead to the evolution of universes that have physical principles most ameniable to the creation of large numbers of massive black holes. And since those principles are co-incidentally also good for the evolution of our form of life...

Interesting conjectures, but at this time basically jsut conjectures. They do, however, have math behind them, that runs waaaaaaay over most peoples heads.

[Clorinox]

"The Big Bang is a creation event"

Wrong! According to basic of physics matter and energy can neither be created or destroyed. It is against the law of physics for anything to be created. Thus there was no creation event. Now energy and matter can change forms and properties, but according to todays scientist everything that is must have always been.

[Clorinox]

"Point to some examples of evolution"

Point to some examples of spontaneously created plants or animals.

[Clorinox]

Sex drives the evolutionary process.
It is through sex that varying genomes can be combined and a different result than the two parents appears. Now does this child have different properties than its parents (within genetic reason)? Yes, its eyes may be a different color, its brain is certainly different, as are its immune system, etc. Now if you take this line of reasoning and expand the sexual lineage down thousands of generations you will see that the great great great, etc. grandchild of this couple will have extremely different properties than the original parents. And if you go far enough (millions of years), odds are the far distant offspring may not even be able to mate with its original ancestors)

Thus evolution of a species through sexual reproduction.

[MeanWestTexan]

Hence, answering the question that the egg came before the chicken, or at least the chicken as we know it today.

[Clorinox]

Indeed, I always thought that, "which came first, the chicken or the egg" was such a stupid question because it is quite obvious to me that the egg obviously originated before the chicken as many lizards including dinosaurs existed well before chickens and used eggs as their reproductive method.

[fr_freak]

Point to some examples of spontaneously created plants or animals.

The ironic part of your demand is that if you follow the theory of evolution to its logical beginning, it requires that at some point life spontaneously erupted.