The domestication of canines was an important step in humanity's rise to world domination, but when did it happen? A genetic study of long dead dogs suggests there were two independent occasions when a human-wolf alliance resulted in the development of our closest companions.

A large team led by Dr. Laurent Frantz of the University of Oxford examined DNA from the remains of 59 dogs that died between 3,000 and 14,000 years ago. This included the complete genome of a faithful companion interred in the tomb at Newgrange, Ireland, remarkably preserved for 4,800 years. This was compared with a wealth of data from modern-day dogs, including 80 full genome sequences.

The team found a major genetic divergence between the genetics of the dogs buried in Europe with those from East Asia, differences sharper than the ones we see today.

The variation was large enough to challenge the idea that humans domesticated dogs once, with all subsequent companions descended from this event, albeit with some interbreeding with wild populations. Moreover, modern European canine genetics are more diverse than ancient specimens.

“Combined, these results suggest that dogs may have been domesticated independently in Eastern and Western Eurasia from distinct wolf populations,” Frantz and his co-authors write in Science. “East Eurasian dogs were then possibly transported to Europe with people, where they partially replaced European Paleolithic dogs.”

^{We were once wolves. Then we discovered sofas. B. Stefanov/Shutterstock}

This east to west canine migration is thought to have occurred between 14,000 and 6,400 years ago, implying a substantial human migration at the time.

For whatever reason, the genetic inheritance of the eastern dogs has proven more successful. Modern dogs, even in Europe, have more genes from the eastern domestication than the one that occurred closer to home.

Greenland sled dogs and Siberian huskies are breeds the paper reports “probably possess mixed ancestry from both Western Eurasian and East Asian dog lineages.” On the other hand breeds such as the Tibetan mastiff appear to be purer representations of the original eastern domestication.

If two events occurred it explains, in part, why scientists haven't been able to get a clear finding of when and where domestication took place. Estimates have ranged from 30,000 years ago to as recently as 12,500 years.

Archaeologists have found some support for the idea of multiple domestication incidents, but until now this has appeared to conflict with genetic studies. However, even these have disagreed on where the event occurred.

“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. 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,” said senior author Professor Greger Larson in a statement.

In the course of the research Frantz also discovered that artificial selection for particular traits is not a new thing – the Newgrange hound had been subject to a similar level of inbreeding to modern dogs.