While researchers have long thought that domestic dogs descended from wolves from at least as far back as 15,000 years ago, the exact geographic origins of the pooches we know and love today has remained a mystery.
But now a new study suggests that there's a reason why the domestication of dogs has baffled scientists, with an international team finding evidence that dogs may have emerged from two separate wolf populations that became domesticated independently from both Eastern and Western Eurasia – what we now know as Asia and Europe. In other words, dogs might have been domesticated by humans twice separately in these two areas, not once, as had previously been thought.
To figure this out, the researchers sequenced the genome of a 4,800-year-old canine from bone excavated from the Neolithic Passage Tomb in Newgrange, Ireland, and looked at DNA sourced from 59 ancient dogs that lived between 14,000 to 3,000 years ago.
They compared this data with the genetic signatures of over 2,500 previously studied modern dogs, and found evidence of a separation that occurred several thousand years ago between East Asian and Western Eurasian dogs – but which took place after archaeological records that suggest the existence of dogs in Europe.
"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 lead researcher Greger Larson from the University of Oxford in the UK.
"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," he added. "Maybe the reason there hasn't yet been a consensus about where dogs were domesticated is because everyone has been a little bit right."
The researchers think that dogs were domesticated separately thousands of kilometres apart on both sides of Eurasia, but then dogs from East Asia migrated with humans westward, largely taking over the Eastern populations.
While records suggest that people and dogs migrated both eastward and westward across Eurasia, it was the dogs from the East that survived in greater numbers.
"Our data suggests that dogs were domesticated twice, on both sides of the Old World," geneticist Laurent Frantz from Oxford told Ben Hirschler at Reuters. "This suggests that at least two groups of humans independently came to the same conclusion: dogs can be domesticated. It also suggests that the process of domestication, while mostly rare, may be replicated more often than we think."
It's an intriguing idea, and one which could explain why genetic traces from both Europe and Central/Eastern Asia are found in modern dogs. But not everybody is convinced by the hypothesis, with other geneticists labelling the paper "provocative" and calling for more evidence to support the claims.
The study authors acknowledge their conclusions remain hypothetical for now, but say new studies combining genomic data with archaelological research will soon help solve the puzzle of where dogs came from - and hopefully with a lot more certainty.
"With the generous collaboration of many colleagues from across the world – sharing ideas, key specimens, and their own data – the genetic and archaeological evidence are now beginning to tell a new coherent story," said one of the team, Keith Dobney from the University of Liverpool in the UK. "With so much new and exciting data to come, we will finally be able to uncover the true history of man's best friend."
You can see the researchers explaining more about their study in the video below.