The researchers obtained mitochondrial DNA -- a type of DNA that is maternally inherited -- from 59 ancient dogs that lived between 14,000 to 3,000 years ago. They then compared all of the data with the genetic signatures of more than 2500 previously studied modern dogs.
Their analysis uncovered a genetic split between modern dog populations now living in Europe and East Asia. The divide seems to have happened after the earliest archaeological evidence for dogs in Europe.
The new genetic evidence also shows that there was a population turnover in Europe, where a smaller, existing dog population was mostly replaced by another bunch of dogs. The researchers think this happened when large groups of people migrated from Asia to Europe, bringing their dogs with them. Probably because of this influx, most dogs today are a mixture of both Eastern and Western dogs, helping to explain the earlier confusion over where dogs originated.
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A review of the archaeological record additionally shows that early dogs appear in both the East and the West more than 12,000 years ago, but in Central Asia no earlier than 8,000 years ago.
"Dogs were domesticated by hunter gatherers, prior to the advent of agriculture," Frantz said. "Dogs most likely provided multiple services to humans, such as facilitating hunting or providing protection."
The researchers can't yet rule out that Neanderthals or some other ancient human first domesticated dogs. Other research teams have found remains for possible dogs going back to the Neanderthal era.
Frantz said that he and his team are currently studying early dogs and wolves using techniques such as 3D scanning to better analyze their features. He explained, "This will allow us to compare wolves at that time with specimens we think may be dogs and to estimate a more accurate time for domestication."
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As for the two or more wolf populations from which dogs first arose, it is possible that they have since gone extinct. The researchers don't think that these wolves were separate species in the biological sense, but were still genetically distinct because they evolved in different regions.
Today's dogs run the gamut from tiny Chihuahuas to large great danes, but they are all still related to the two or more founding wolf populations, according to the researchers.