Humans domesticated dogs not once, but twice, on both sides of the 'old world', scientists have said. Scholars have long been divided over the origins of man's best friend: some argued that the species was first domesticated in Europe, while others retraced its first appearance at humankind's side back to Eastern Asia.

The latest study, published in Science, suggests that both of these theories may be correct. Looking at extensive archaeological and genetic data, the scientists have gathered the first concrete evidence that two ancient and distinct populations of wolves may have been domesticated by men, in different regions and at different stages of history.

The team, led by scientists from Oxford University in the UK, reconstructed the evolutionary history of dogs in order to understand how they emerged, and then settled across the whole of Eurasia – the continental landmass of Europe and Asia.

Confronting archaeological and genomic data

The well-preserved bone of a 4,800-year-old dog excavated from a Neolithic tomb in Ireland was used to produce a detailed sequencing of the animal's genome.

The researchers also obtained the mitochondrial DNA from 59 ancient dogs and wolves that lived in Europe and Asia between 14,000 and 3,000 years ago.

This genetic information was compared with the genome of 2,500 modern-day dogs and wolves from around the world. The scientists constructed an evolutionary 'tree' to assess how different dog populations might have moved across Eurasia and evolved over the years.

dogs domestication
Dogs have been domesticated separately in Asia and Europe from ancient wolf populations Jeff Pachoud/AFP/Getty

The genetic analysis highlights a deep divide between today's dogs living in East Asia and Europe. Both populations appeared to have had a common ancestor, and to have diverged sometime between 6,400 and 14,000 years ago.

However, archaeological remains bring evidence that there were already domesticated dogs in these two regions 15,000 years ago, before the appearance of the common ancestor. This suggests that dogs had already been domesticated in Europe by the time that Asian dogs arrived with their masters and progressively replaced early European dogs.

"Our genetic data tells us there might have been two separate domestications, one in each region. It shows that there was population movement from the East to the West, which led to the earliest domestic dogs in Europe being replaced", lead study author Dr Laurent Frantz told IBTimes UK.

Thus the scenario of two separate domestications of dogs before both groups met and mixed appears plausible. "Most animals were domesticated once from a single wild population, and what we have now is what we believe to be the first evidence both genetically and archaeologically were in fact domesticated two times", senior author Professor Greger Larson has said.