|Who is that doggy in the window?|
|Scientists trace the origin of dogs|
|By Kate Dalke
November 22, 2002
Best friends, dog and man. Our canine pals console us with wagging tails and wet kisses when we've had a bad day. We, in turn, go for long walks in the woods with our pooches, pockets filled with doggy biscuits.
Where and when did this famed friendship begin? Two new studies bring us closer to some answers. Scientists have discovered that all dogs are descended from gray wolves in East Asia about 15,000 years ago. These include so-called "New World" dogs that came across the Bering Strait with humans many thousands of years ago.
A third study, also published in Science, confirms that dogs are perhaps the most perceptive species when it comes to recognizing and interpreting human behavior.
Dogs and their genomes have perked some ears lately. The US National Institutes of Health announced earlier this year plans to sequence the dog genome, providing clues about behavior, disease and perhaps evolution.
Dogs descended from wolves, most scientists agree. But there is no consensus about the details of wolf domestication. Not to mention about why dogsor humans'decided' to live closer together, putting their fears aside.
"The origin of the dog, in itself, is an important part of human history," says Peter Savolainen of the Royal Institute of Technology in Stockholm, Sweden, who led the study that traced all dogs to wolves in East Asia. Previous studies suggest the origin of the species was Europe or the Middle East.
Savolainen and his collaborators analyzed mitochondrial DNA from the hair of some 650 dogs from Europe, Asia, Africa, and the Americasand from 38 Eurasian wolves.
All the DNA sequences belonged to three related groups with a "common origin from a single gene pool," the researchers write in Science. The most genetic variation occurred in dogs that hail from East Asia, which led to the conclusion that this region is the most likely origin of the species.
The date of about 15,000 years ago as the time of domestication is based on the number of genetic mutations dogs have accumulated in their DNA compared to their wolf ancestors.
In the second study, scientists used DNA fingerprinting techniques to show that New World dogs were not descended from wolves in the Americas. Rather, these dogs were descendents of wolves in Asia and Europe.
Thus, it appears that New World dogs traveled with the humans who reached North America across the Bering Strait.
"We were surprised to see the same DNA sequences in the New World and Eurasian dogs," says Carles Vilà of Uppsala University in Sweden, who led the study.
To get accurate representatives of early New World dogs, the scientists had to literally 'go digging' for DNA. They collaborated with archeologists in Mexico and Peru and extracted DNA from the bones of dogs deposited before the arrival of Columbus.
Based on examinations of dogs from places as distant as Peru and Alaska, the researchers hypothesize that "ancient and modern dogs worldwide share a common origin from Old World gray wolves."
These New World dogs were eventually wiped out of the population and are no longer present in modern dogs. Apparently European colonists systematically discouraged the breeding of Native American dogs.
"The study suggests European dogs basically replaced dogs that came over with the earliest Indians," says Niels Pedersen of the Veterinary Genetics Laboratory at the University of California, Davis.
The findings confirm that the modern dog is not the descendent of modern wolf, notes Pedersen.
"There is no American wolf blood in modern dog," says Pedersen.
No known Native American dog exists. Even the Mexican hairless dog, a breed previously thought to have been developed in the Americas over 2000 years ago, has mostly European genes.
So if dogs have just a handful of common ancestors, where did all these strikingly different breeds come from? From the dog's two-legged friends, say researchers.
"Most breeds have developed during the past 500 years," says Savolainen. Before humans began breeding dogs for certain traits or behaviors, dogs were more general in their appearance or morphology.
Breeds tell us more about human preferences than about dogs, says Vilà. "Dog breeds are the result of human preferencesselected traits taken from generation to generation."
"These studies force us to reconsider how humans were living during these times," he adds. "Humans were not living by themselves; somehow dogs benefited humans and helped them survive.
Pedersen agrees. "It was advantageous for dogs to stay close to humans. These studies suggest that dogs and humans co-evolved."
In the third study in Science, researchers confirm what most dog owners already know: Their companions are more perceptive than other animals in responding to human behavior. Even more perceptive, it turns out, than our closest relative, the chimpanzee.
Brian Hare of Harvard University in Cambridge, Massachusetts, designed the study to confirm his belief that his own dogs, a Labrador retriever and a mixed breed, had superior skills in responding to his behavior.
Hare hypothesizes that these skills were honed during the domestication of dogs because animals that could use social cues to predict human behavior were at a selective advantage. This is the first study to confirm there have been cognitive changes during domestication, he adds.
Next, he plans to investigate the genetics underlying behavioral traits by studying a population of silver foxes in Siberia. Known as Belyaev's silver foxes (for the man who tamed them), these foxes have been experimentally domesticated over 30 generations.
"When you domesticate a species, a suite of changes occurs," says Hare. He will work with a geneticist to try to identify changes in the Belyaev fox genome associated with changes in behavior.
Before he can do that, Hare must answer the email and phone calls from dog owners interested in his research.
"You wouldn't believe the people who have been calling me lately," he says. "I just received a call from a man who says his dog can do math."
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