Posted on 12/21/2004 8:45:42 AM PST by 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.
Deliberate manipulation, by humans, of the genetic makeup of dogs has routinely, in hundreds (maybe thousands) of years, produced dogs that can literally eat other dogs in one bite. I wonder what nature (evolution) could do in billions of years. Oh, Oh, Oh... I think I know the answer... it's called evolution by natural selection.
Good Lord.
29+ Evidences for Macroevolution. Yes, macro-evolution.
Transitional Vertebrate Fossils FAQ. Yes, transitional fossils exist.
Fossil whale with legs. Land animal to whale transitional fossil.
Feathered Dinosaurs.
Archaeopteryx. Reptile-to- bird transitional fossil.
Archaeopteryx: FAQS . A true transitional fossil
All About Archaeopteryx.
Human Ancestors.
The Evidence for Human Evolution. For those who claim there isn't any evidence.
Comparison of all Hominid skulls.
Observed Instances of Speciation. That's right ... observed!
Ring Species. We can observe two species and the intermediate forms connecting them.
Ensatina eschscholtzi: Speciation in Progress. A Classic Example of Darwinian Evolution.
Did he chomp the Rott's balls from underneath, or what?
The definition of "species" found in the Mirriam-Webster Online dictionary is as follows:
1 a : KIND, SORT b : a class of individuals having common attributes and designated by a common name; specifically : a logical division of a genus or more comprehensive class
(1) : a category of biological classification ranking immediately below the genus or subgenus, comprising related organisms or populations potentially capable of interbreeding
The genus "Canis" includes a number of species, among them wolves, domestic dog, dingos, jackals, and coyotes.
Tiny dogs like Chihuahuas, and giant dogs like the wolfhounds or mastiffs, are POTENTIALLY capable of interbreeding. So they are members of the same species. However, such radically different breeds of dogs (or goats, or other domestic animals) are actually different subspecies.
The rank is genus; within genus, species; with species, subspecies. Subspecies occur both in nature and as a result of human domestication.
The existence of cats disproves the possibility of natural selection.
The existence of humans disproves the possiblity of intelligent life.
That's been a pet theory of mine for quite some time. Someone I know once termed them "punt" sized dogs.
Over much less than geological timespans, free oxygen in planetary environments goes away. Yes, you'll get atomic oxygen forming above the atmosphere as UV breaks water molecules down, but that is a very miniscule fraction of the oxygen bound up in the whole syste,.
> I made an assertion.
Yes, you did.
> Point to some examples of evolution.
Read the article that started off this thread, for starters. Then google on "speciation" and "observed."
> I'm saying your argument that an unintelligent something created time, matter, energy and the Laws of Physics ex nihilo laughable.
That's nice. Too bad modern quantum mechanics don't agree with you.
Oh really? Why don't you entertain us with your treatise on how quantum mechanics allows for the creation of mass and enrgy ex nihilo. We'll save time and the Laws of Physics for later.
Ah so it is.
http://www.snopes.com/humor/iftrue/chihuahua.asp
Thanks
See post # 214
Too bad.
Obviously, you're not even one of the mediocre minds because you can't read. I didn't bring up Quantum Mechanics, the other guy did.
Actually mass and energy cannot be created or destroyed.
And yet mass and energy were created in viloation of the Conservation Laws. Weird huh?
it can only be transformed from one state to the other E=Mc sqrd.
Evidently not, the laws did not apply at t=0+.
Your argument is false.
You'll understand if I don't treat those words as if Moses brought them down from the mount.
Big bang theory is not stating the mass and energy are created out of nothing. (I assume that is where you are trying to go?)
BBT, as I understand it, assigns the "singularity" responsibility for the creation of matter, energy, time and space et al. Where'd the singulairty come from, WalMart?
Further, speaking in generalities, if you want to bring Quantum theory in to a debate on evolution, Quantum theory is all about probabilities.
The probability that I brought Quantum Theory into the debate is null.
Not about pre determined paths. That is the old God does not play dice line. If you want to bring in Quantum theory, then you subscribe to God playing dice. Hardly a sign of intelligent design.
Does God consult with you often on the mechanisms he uses?
> your treatise on how quantum mechanics allows for the creation of mass and enrgy ex nihilo.
Not mine. But there are several theories. Feel free to look them up. Here's a start:
http://slate.msn.com/id/2100715/
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