The precise origin of our canine companions is mired in controversy. But a new study suggests that dogs emerged from not one but two different populations of ancient wolves. What's more, this dual domestication happened on opposite sides of the Eurasian continent. A modern wolf. (Image: Shutterstock)
Dogs first appeared about 15,000 years ago, long before the advent of agriculture, and represent the earliest known domestic animal. They emerged from ancient wolves, but scientists aren't entirely sure if this seminal domestication event happened in Europe or Asia. A new study published in Science suggests there's truth to both of these claims.
Previous studies have concluded that dogs were likely domesticated just once, but the timing and origin of this event has been hotly debated. Complicating the matter is conflicting archaeological evidence showing that early dogs resided on either side of the Eurasian continent many thousands of years ago. The new study shows that dogs were likely domesticated on at least two different occasions and in two different parts of the world.
An ancient cave painting of a wolf-like canine, Font-de-Gaume, France. (Credit: Henri Breuil)
By comparing genetic data with archaeological evidence, an international team of researchers led by the University of Oxford has shown that dogs emerged independently from two separate wolf populations (or more accurately, now-extinct ancestral wolves that are common ancestors of both modern wolves and dogs) that lived in West and East Eurasia. This means that two different populations of paleolithic humans independently came to the same conclusion: these intelligent four-legged animals could be bred to live and work among humans.
A critical piece of the puzzle was uncovered several years ago at the Neolithic Passage Tomb of Newgrang in, Ireland. This site yielded a 4800-year-old medium-sized dog, the DNA of which could still be extracted.
"The Newgrange dog bone had the best preserved ancient DNA we have ever encountered, giving us prehistoric genome of rare high quality," said senior author Dan Bradley from Trinity College Dublin. "It is not just a postcard from the past, [but] rather a full package special delivery."
Bradley's team, with the assistance of researchers from the National Museum of National History in Paris, also collected and analysed the mitochondrial DNA from the remains of 59 ancient dogs that lived between 3000 to 14,000 years ago. Their genetic signatures, including those of the Newgrange dog, were then compared to the genomes of more than 2500 previously studied modern dogs.
"Reconstructing the past from modern DNA is a bit like looking into the history books: you never know whether crucial parts have been erased," said lead author Laurent Frantz in a statement. "Ancient DNA, on the other hand, is like a time machine, and allows us to observe the past directly."
Map showing the geographic origin and age of the oldest archaeological dog remains in Eurasia. (Image: L.A.F. Frantz et al, 2016)
This data indicates a deep genetic split between dogs from two disparate geographical regions, several millennia after the first known appearance of dogs in Europe and East Asia. It also appears that there was a dramatic population turnover event in Europe, one that effectively replaced the earliest domesticated dog populations living there. This implies an influx of different dogs from elsewhere, namely East Asia. According to the research, these forebearers of modern dogs appeared in both the western and eastern Eurasia more than 12,000 years ago, but no earlier than 8000 years ago in Central Asia.
The new model of dog domestication under dual-origin hypothesis. (Image: L.A.F. Frantz et al., 2016)
Here's what likely happened: An initial population of ancestral wolves split into East and West Eurasian wolves that were then domesticated independently before going extinct. At some point after this dual domestication event (about 6400 years ago), the eastern dogs travelled to Europe with their migrating human companions, after which time they mixed and partially replaced the earliest European dogs.
Today, most dogs are a hybrid of both eastern and western dogs. This explains why scientists have had such a hard time deciphering the DNA of modern dogs. The researchers say that some breeds, like the Greenland sledge dog and Siberian husky, appear to possess mixed ancestry from both Western Eurasian and East Asian dog lineages.
This new research answers a bunch of unresolved questions -- but more work still needs to be done. It's not implausible, for instance, that a single origin story exists for Eurasian dogs, followed by early transportation to Europe. Trouble is, there's a lack of archaeological evidence to support this.
Looking ahead, the researchers would like to combine ancient and modern genetic data with detailed physical analysis and archaeological research to develop an improved timeline of events, and to better establish the geographical origins of man's best friend. Another good idea would be to do a comparative analysis of ancient dogs with the Australian dingo, which is likely descended from East Asian dogs. Should the dingo lack any traces of European DNA, that would further bolster the new dual origin theory.