Humans may have domesticated dogs two separate times, taming wolves both in Europe and Asia thousands of years ago, according to new research.
A major international research project may have cleared some of the controversy surrounding the origins of man's best friend, which has until now remained a mystery with two primary hypotheses.
The first holds that humans domesticated dogs for the first time in Europe more than 15,000 years ago.
Opposing researchers believe the domestication happened approximately 12,500 years ago in Central Asia or China.
The new study, published in the American journal Science, suggests both claims might carry weight.
"Maybe the reason there hasn't been a consensus about where dogs were domesticated is because everyone has been a little bit right," Oxford University Greg Larson said.
Researchers used ancient DNA evidence and the archaeological record of early dog species in their research.
The project involved sequencing for the first time the genome of a 4,800-year-old dog at Trinity College in Dublin.
That dog's bones came from the Neolithic Passage Tomb of Newgrange, Ireland, a contemporary of Stonehenge in England.
The team also used mitochondrial DNA from 59 ancient dogs who lived between 14,000 and 3,000 years ago, comparing the samples to genetic traits of more than 2,500 modern dogs.
Theory could prove domesticating animals 'easier than thought'
Their findings suggested dogs were separately domesticated both in Europe and in Asia, and later mixed as humans migrated across the continent, meaning most dogs today were a genetic mix of their Asian and European ancestors.
The new hypothesis would explain in part why scientists have had a hard time interpreting previous genetic studies.
The double-origin theory could also suggest that cats and pigs were domesticated multiple times, said Peter Savolainen, a geneticist at the Royal Institute of Technology in Stockholm.
"If domestication only happened in one place, it was probably a very hard thing to do," he said.
"But if it happened twice, maybe it wasn't as hard as we thought."