Scientists are beginning to find clues as to how or why there are so many varieties of dogs and the mechanisms that allow that. From the Dallas News:
Dozens of new dog breeds have taught Dallas scientists one of evolution's very old tricks. The researchers have uncovered a previously unappreciated genetic mechanism that, over millions of years, may have helped sculpt the many different shapes of the world's animals.The findings – based on a gene that helps give dog breeds their distinctive head shapes – may also explain how massive St. Bernards, tiny Chihuahuas and everything in between descended from the wolf in just a few thousand years.
Understanding this genetic process could also give scientists new clues to the development of the human form and brain, as well as the rampant growth of cancers.
"We're just beginning to scratch the surface of all the gadgets and tools that nature has come up with," said John "Trey" Fondon, one of the biologists from the University of Texas Southwestern Medical Center at Dallas who performed the new research. "This is just one of them. But what it says is that we don't know nearly what we think we know about how evolution works."
The report describing the research, released Monday, appears online in the Proceedings of the National Academy of Sciences.
Not too long ago there was a show about this subject on Nova. What they found was that a fox breeder in Russia wanted to breed the aggressive nature out of them, and so he started doing so by selecting the most passive, domesticated foxes for breeding. What happened was the amount of adrenalin in the fox’s system dropped, and as that happened they started barking, and their ears started to droop and move down on their heads.
I wish I could remember more, but that is essentially what they said, and it is one theory on how we came to have such a variety of dogs.
The fox effect is pretty easy to explain; floppy ears, increased barking, and other traits- like the fluffy coat with odd markings that made the "domesticated" foxes useless as fur farm products- are all puppylike qualities. Biologists call it "neoteny", which means retention of juvenile traits into adulthood. Docility (relative to their normal adult attitude, anyway) is a juvenile trait for carnivores, so selecting for it tends to bring much of the rest of the package along.
As for the mechanism discussed in the article, from the PNAS abstract it appears to be variations in repeating patterns in certain developmental genes, particularly in limb and skull design. High-frequency mutations and incremental effects of same can mean big changes in short periods of time that selection (natural or in this case artificial) can easily work on.
Posted by: LabRat at December 15, 2004 07:03 PM