Humankind’s long friendship with the dog may have begun at least twice. Grey wolves in western Eurasia may have started hanging around Stone Age hunter-gatherer clans even before humans and dogs clinched the relationship perhaps 14,000 years ago in east Asia.

New research based on DNA samples from prehistoric hounds, as well as genetic studies of modern dogs and wolves, suggests that two populations of grey wolves – separated by thousands of miles and thousands of years – may have begun the connection that turned Canis lupus into Canis lupus familiaris.

The scientists say in the journal Science that their scenario remains hypothetical. Researchers have been arguing about the origins of the spaniel, the terrier and the collie for more than a decade.

“Animal domestication is a rare thing and a lot of evidence is required to overturn the assumption that it happened just once in any species,” said Professor Greger Larson, one of the authors and the director of the Wellcome Trust palaeogenomics and bio-archaeology research network at Oxford University.

Scientists show that dogs were domesticated twice - video. Source: University of Oxford

“Our ancient DNA evidence, combined with the archaeological record of early dogs, suggests that we need to reconsider the number of times dogs were domesticated independently. Maybe the reason there hasn’t been a consensus about where dogs were domesticated is because everyone has been a little bit right.”

The domestication of cattle, sheep and goats began with the first farm settlements in the Fertile Crescent at the end of the last Ice Age 10,000 years ago. The only animal known to have been domesticated twice is the pig, in both east Asia and the near East. The same story might be true for Rover and Fido. If so, grey wolves must have started hanging around human settlements for food scraps: the step from scavenger to hunting companion would have taken many generations.

Modern dogs seem to share a common origin: in 2005 geneticists looked at canine DNA and decided that all 400 modern breeds and all 400 million modern dogs had descended from grey wolves that lived in eastern Asia perhaps 15,000 years ago.

But much older bones found with human remains also seemed to show evidence that dogs and humans teamed up in Europe long before that distant befriending event far to the East.

Then Laurent Franz from Oxford University and colleagues began looking at samples of mitochondrial DNA – inherited only from the mother, and therefore a sure guide to ancestry – taken from the bones of 59 European dogs that lived between 3,000 and 14,000 years ago. They also looked at the entire genome of a dog found buried at Newgrange in Ireland, dating from about 5,000 years ago. Then they compared the ancient DNA with that from 2,500 modern dogs and wolves.

This revealed evidence of a separate origin which could not be detected in modern dogs because contact between prehistoric humans from east Asia and west Eurasia would have led to interbreeding, scrambling the genetic evidence. The Oxford scientists, however, could not make the direct link with a different wolf ancestor in the west because this proposed “ghost” population would have long since disappeared.

“Once you have a domestic animal, the wild animal becomes a problem. It’s the same for the aurochs, the wild ancestor of cattle: there’s none of them left either. Or the dromedary camel. We have a very long and proud history of killing all kinds of things,” Larson said. “The population of wolves that gave rise to dogs simply doesn’t exist anymore.”

To settle the question, the researchers are looking at more dog and wolf samples from Stone Age Europe for evidence of a dog-wolf connection that could only have begun in the west.

“That would be the smoking gun. Equally, if we get the early Mesolithic and Neolithic dogs and wolves of western Europe and they look very much like modern dogs then the hypothesis of two origins becomes a lot less tenable. We will have an answer one way or another to this question.”

Besides the dogged pursuit of canine origins, Larson’s lab is working on other domestication puzzles: the story of wild boars and domestic pigs, of jungle fowl and chickens and the first water buffaloes.

“Everything has this unique story,” he said. “Pigs are still the only thing we know where there was more than one.” And though he grew up in a dog-owning family, he does not have a dog himself. “I get asked this every six seconds. I wish the answer was yes.”