WASHINGTON (AP) Fido may be cute, cuddly and harmless. But in his genes, he's a wolf.
Researchers tracing the genetic family tree of man's best friend have confirmed that domestic dogs, from petite poodles to huge elkhounds, descended from wolves that were tamed 100,000 years ago.
"Our data show that the origin of dogs seems to be much more ancient than indicated in the archaeological record," said Robert K. Wayne of UCLA, the leader of a team that tested the genes from 67 dog breeds and from 162 wolves on four continents.
The study suggests that primitive humans living in a hunting and gathering culture tamed wolves and then selectively bred the animals to create the many different types of dogs that now exist.
Wayne said in a statement that DNA sequences of the animals also confirms that wolves are the only true ancestors of domesticated dogs.
The study is being published Friday in the journal Science.
Stanley J. Olson, a University of Arizona vertebrate paleontologist, said Wayne and his colleagues make a "logical argument" but need more evidence, such as canine bones found at places where ancient humans lived.
"It could have happened 60,000 years ago or more, but we have no physical evidence, such as bones and so forth, to prove that," said Olson. "All of the materials I have seen indicates that the taming and domestication probably happened 10,000 to 14,000 years ago."
Olson said there is evidence that primitive humans and wolves lived near each other and probably benefited from the relationship. Wolf packs, he said, probably got some of their food from carcasses left behind by hunting humans. It's possible, he noted, that wolf packs incorporated human bands into a territory protected from other packs.
"They could have become like natural watchdogs," he said.
It is also likely, said Olson, that primitive humans raided wolf dens, captured pups and then raised the ones that showed promise of being tamed.
"Once they started feeding these animals, they probably couldn't get rid of them," he said. "It's clear that we like dogs and they seem to like us. That could be how it started."
In the new study, Wayne and his associates studied patterns in the mitochondrial DNA from dogs, wolves, coyotes and jackals. This type of DNA changes at a specific rate. The number of changes increases with time.
Wayne said the study showed so many DNA changes that dogs had to have diverged genetically from wolves 60,000 to more than 100,000 years ago.
"We have found that the origin of dogs is much older than previously believed because the genetic diversity within dogs is much greater than if their origin was as recent as 14,000 years," Wayne said in a statement.
The researchers found four distinct genetic groups in the dog world. This suggests that wolves may have been tamed and domesticated several times, at different times and places, and that no single wolf ancestor is common to all dogs. It also suggests that dogs and wolves could have interbred later, adding fresh wolf DNA to the domestic dog gene pool.
But no DNA evidence was found of coyotes or jackals in the dog family tree. The study showed that Fido, and every other dog in the world, was all wolf, the researchers said.