LOS ANGELES — When it comes to evolutionary debates, this one is a major dogfight.
Since the time of Charles Darwin, scientists have argued over the origin of domesticated dogs and how, when and where a toothy, flesh-eating beast was transformed into man’s best friend.
Some experts believe our ancestors in the Middle East and elsewhere were naturally drawn to small, furry wolf pups and seized them as novelties. Others suggest they were raised as a source of meat in early agrarian societies in Asia.
Yet another theory holds that early proto-dogs were enlisted as helpers by roving bands of hunters, long before humankind ever experimented with agricultural livestock.
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Now, thanks to faster and cheaper DNA-sequencing technology, this argument over what sparked the Big Bark may be drawing to a close.
After analyzing the mitochondrial genomes of 18 ancient dogs and wolves and comparing them with an array of modern counterparts, evolutionary biologists have concluded that dog domestication most likely occurred in Ice Age Europe 18,800 to 32,100 years ago. That’s much earlier, and much farther north, than previously believed, according to the researchers’ report published Thursday in the journal Science.
Dogs, the authors wrote, evolved from a now extinct species of European wolf that followed bands of nomadic or seminomadic humans who were hunting woolly mammoths and other large prey.
Initially, the wolves sought out the carcasses and scraps of meat left behind by people. Over time, these hang-around wolves began to fill a special role in human hunter-gatherer society, the researchers surmised.
“The initial interactions were probably at arm’s length, as these were large, aggressive carnivores,” said UCLA evolutionary biologist Robert Wayne, the study’s senior author. “Eventually, though, wolves entered the human niche. … Maybe they even assisted humans in locating prey, or deterred other carnivores from interfering with the hunting activities of humans.”
As these wolves migrated along with people, they became isolated from other wolves. The docile wolves bred and stuck with their new human friends. They stopped intermingling as much with the wild wolves.
After generations upon generations of selective breeding, wolves slowly became more like the dogs of today, still the only large carnivore ever domesticated, Wayne said. They even adapted to a high-starch diet, leaving them in better shape during human society’s later forays into agriculture.
After being welcomed into human society in Europe, domesticated dogs spread across the Old World, and then to the Americas. The robust European wolf that got the fetch ball rolling left no living descendants other than dogs.
“Wolves living on the planet today are not the closest group to the ancestor of dogs,” said Wayne, who conducted the research with colleagues in Germany, Finland, Belgium, Russia, Spain, Argentina and the United States.
Until recently, many archaeologists and biologists believed that dogs were first domesticated no more than 13,000 years ago, either in East Asia or the Middle East. One key find was a burial site in Israel that contained the 12,000-year-old remains of an elderly man cradling a puppy, evidence of the unique bond between dogs and humans.
Tracing the exact path of dog evolution has been extremely difficult. Ancient dog remains are hard to distinguish from wolf remains, and frequent interbreeding between dogs and wolves further complicates matters. Add to that mankind’s zealous breeding of dogs to enhance specific traits and behaviors and the genetic water becomes very cloudy.
Darwin believed that the dizzying variety of dog breeds argued strongly that dogs must have had more than one wild ancestor. Genetic researchers today say this is most likely not the case and that domesticated dogs evolved from one ancestor, in one region.
“On some levels, understanding the geographic origins of dogs is definitely more difficult than studying humans,” said Greger Larson, a bioarchaeologist at Britain’s Durham University.
Larson, who was not involved in the Science paper, said Wayne and his colleagues had “significantly advanced” the debate on domestication.
“I really like this paper,” Larson said. “Dogs have always been hard to pin down, and there have always been crazy ideas about the process and the location. But the emergence of genetic methods … has elevated the level of discourse.”
There are those, however, who argue that Wayne and his colleagues are barking up the wrong genetic tree.
Peter Savolainen, an associate professor of evolutionary genetics at Sweden’s Royal Institute of Technology, said there was plenty of evidence that dogs were first domesticated in China, probably as a source of food.
Savolainen pointed out that Wayne and his colleagues published a paper in 2010 citing the Middle East as the origin of domestic dogs, a view they have now abandoned. “They don’t comment on that in this paper and they should,” Savolainen said.
He also noted that the Science study lacked animal samples from the Middle East or China. “If you only have European samples, obviously you will find that Europe is the origin,” he said.
“What they need to have is samples from south China,” he said.
There’s just one catch. South China is now so densely settled by people that no wolves live there.
Wayne said he and his colleagues did not include samples from outside Europe because they were too recent, only about 7,000 or 8,000 years old. “That’s well after dogs were domesticated, so we’re kind of limited in that sense,” he said.
As for the turnabout on the Middle East hypothesis, Wayne said it was based on new genetic evidence and the realization that domesticated dogs interbred with local wolf populations, confusing the genetic signal.
“Initially, we didn’t appreciate how important that early admixture was,” he said.
The study authors said they hoped to confirm their findings with additional testing of genetic material from the nuclei of ancient cells. This type of DNA contains abundantly more information than DNA taken from mitochondria, tiny structures outside the nucleus that produce energy for the cell.
In the meantime, experts are left to ponder this latest development, as well as the reason why the scientific stakes seem so high.
“People make up tremendously elaborate stories about the origin of our own species based on a few fossil remains here and there,” said James Serpell, a professor at the University of Pennsylvania School of Veterinary Medicine who wasn’t involved in the study. “I guess we’re doing the same thing now to our dogs. We view them as members of our families and we want to know where they came from and how this relationship came about.”
Material from The New York Times and The Washington Post is included in this report.