Dog domestication happened just once, ancient DNA study suggests

Like pups worrying over a bone, debate over when — and how many times — dogs were tamed continues

dog skull

HEAR HEAR  DNA extracted from an inner ear bone of this dog skull is helping researchers decipher dogs’ origin story. The skull is about 4,700 years old and was found at Cherry Tree Cave in Germany.

Amelie Scheu

People and pooches may have struck up a lasting friendship after just one try, a new genetic study suggests.

New data from ancient dogs indicates that dogs became distinct from wolves between 20,000 and 40,000 years ago, researchers report July 18 in Nature Communications. Dogs then formed genetically distinct eastern and western groups 17,000 to 24,000 years ago, the researchers calculate. That timing and other genetic data point to dogs being domesticated just once.

That idea contrasts with a hypothesis put forward last year that dogs were domesticated separately in Europe and East Asia, with the Asian dogs eventually replacing the European mutts (SN: 7/9/16, p. 15).  

Scientists agree that dogs stem from wolves, but where, when and how many times dogs were domesticated — passing down tameness and other traits over generations — has been rethought many times in the last few years (SN: 7/8/17, p. 20).

The new study “puts dog origins into one time and place again. That’s really important,” says Peter Savolainen, an evolutionary geneticist at KTH Royal Institute of Technology in Stockholm who was not involved in either study. These new data indicate “there’s a single origin, and it wasn’t in Europe,” says Savolainen, a proponent of an East Asian origin of dogs.

The new study examined the complete genetic blueprints, or genome, from a 7,000-year-old dog from Herxheim in Germany, and a 4,700-year-old dog from Cherry Tree Cave (also known as Kirshbaumhöle) in Germany. The scientists also analyzed DNA data from a 4,800-year-old dog from Newgrange, Ireland, that had been described in the previous study positing two domestication events.

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CAVE DOG The skull of a 4,700-year-old dog (center, right of the marker stick) was found in Cherry Tree Cave in Germany. The dog is analyzed in a new genetics study suggesting that dogs were domesticated only once. Timo Seregely.

A claim of multiple domestications for dogs requires extraordinary evidence, says study coauthor Krishna Veeramah, an evolutionary geneticist at Stony Brook University in New York. But complete genomes of the ancient dogs suggest a simpler story. “We can explain all of our data just using one domestication event,” Veeramah says.

Although Veeramah and colleagues see a split between eastern and western dogs, that split probably happened after domestication took place. Modern European dogs still share heritage with Stone Age canines on the continent, hinting that all the pups came from a common source rather than separately domesticated Asian dogs replacing their European counterparts.

These new data don’t completely rule out multiple domestications (the single event is just the simpler explanation), nor do they indicate where humans and canines became BFFs, Veeramah says. A family tree constructed from the DNA data puts today’s Southeast Asian breeds on the earliest branch, implying an origin in Asia. But a dog breed’s present-day location may not reflect where dogs were actually domesticated more than 20,000 years ago, Veeramah says.  

The team that proposed double domestication is not convinced of a single origin. The new study is based on genetic data alone and doesn’t take archaeological evidence into account, says Greger Larson, an evolutionary geneticist at the University of Oxford.

“There’s no smoking gun here, and there’s no direct contradiction,” says Larson. “Our hypothesis of a dual origin remains a possibility, as does a single origin.” Researchers won’t know for sure until they’ve analyzed older dogs from multiple places.

The ancient doggy data also challenge a recently proposed idea that dogs were domesticated when early mongrels developed the ability to digest starch better than wolves could (SN Online: 1/23/13), allowing them to eat grains in early farmers’ trash heaps. A previous study found that today’s dogs have many copies of the AMY2B gene, which produces an enzyme that helps break down starch, while wolves have only two copies.

The new study finds that both ancient German dogs had two copies of AMY2B, while the Newgrange dog had three. Since those dogs lived thousands of years after domestication, the findings suggest the first domesticated dogs were no better equipped to digest starch than wolves were. But the ancient dogs do have other genetic variants that made it possible for the amylase gene to be copied later, Veeramah says. Exactly when that happened isn’t clear.

Tina Hesman Saey is the senior staff writer and reports on molecular biology. She has a Ph.D. in molecular genetics from Washington University in St. Louis and a master’s degree in science journalism from Boston University.

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