The claim remains just a hypothesis, according to the authors of a paper published Thursday in the journal Science. But they say their analysis of genetic and archaeological evidence makes it the best explanation for a long-standing conundrum that has been hard to solve in part because breeding has made today’s dogs, which all have roots in Asia, so genetically scrambled.
To come to this conclusion, the researchers, who are part of a major project on dog origins based at the University of Oxford in Britain, looked at DNA sequences from the remains of 59 ancient European dogs ranging in age from 3,000 to 14,000 years old. But they also had a complete genome taken from a 4,800-year-old fossil of a dog’s inner ear bone, which was dug up at the Newgrange archaeological site in Ireland. They compared these to DNA from hundreds of modern dogs.
What they saw was a dramatic genetic split between the modern European and East Asian dogs. But when did it happen?
To figure this out, the Newgrange dog was key. Knowing its age allowed them to calculate a genetic mutation rate — or “calibrate an internal molecular clock,” said co-author Greger Larson, an Oxford evolutionary biologist. And that indicated that the East-West divide happened between 6,400 and 14,000 years ago. Here’s a Science magazine video that illustrates the idea:
This could mean that dogs were domesticated first in East Asia and then migrated West, maybe with their new human pals. But the earliest archaeological remains of dogs found in Europe are at least 15,000 years old — before the split they calculated occurred. What’s more, a movement from east to west would have left a timeline of dog fossils scattered in the geographic area in the middle. And those haven’t been found.
“In between, we do not find any dogs earlier than 8,000 years old. We find human settlements there, but we don’t find dogs,” said lead author Laurent Frantz, an evolutionary geneticist at Oxford. “If dogs were domesticated only once and transported from east to west, we should find these gradients, and we can’t find it.”
So they hypothesized that two populations of now-extinct wolves, one in Europe and one in Asia, were domesticated independently. Dogs later migrated from Asia to Europe, and their genetics pretty much engulfed the original dog populations in the West. They emphasize, though, that lots more testing, including of well-preserved ancient dog remains from Europe, is needed to help prove it.
Dual domestication happened before, with pigs, Frantz pointed out. And though the explanation isn’t as neat as a single-origin tale, he said he thinks it could serve to calm the east-west dispute that dogs canine science.
“I think what this paper is really showing is that these can be reconciled,” he said.