Part of the ancient mystery of the makeup of the modern Western dog has been solved by a team led by researchers at the University of California, Davis, School of Veterinary Medicine.

Several thousand years after dogs originated in the Middle East and Europe, some of them moved south with ancient farmers, distancing themselves from native wolf populations and developing a distinct genetic profile that is now reflected in today’s canines.

These findings, based on the rate of genetic marker mutations in the dog’s Y chromosome, supply the missing piece to the puzzle of when ancient dogs expanded from Southeast Asia. The study results are published online this month in the journal Molecular Biology and Evolution.

“Our findings reconcile more than a decade of apparently contradictory archaeological and genetic findings on the geographic origins of the dogs,” said Ben Sacks, lead study author and director of the Canid Diversity and Conservation Group in the Veterinary Genetics Laboratory at the UC Davis School of Veterinary Medicine.

Considerable archaeological evidence indicates that the first dogs appeared about 14,000 years ago in Europe and the Middle East, while dogs did not appear in Southeast Asia until about 7,000 years later. Scientists have been puzzled, though, because growing genetic evidence suggests that modern Western dogs, including modern European dogs, are derived from a Southeast Asian population of dogs that spread throughout the world.

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The problem: If dogs originated in Europe, why does genetic evidence suggest that modern European dogs are originally from Southeast Asia? Sacks and his team think they’ve found the answer.

“Data from our study indicate that about 6,000 to 9,000 years ago, during what is known as the Neolithic age, ancient farmers brought dogs south of the Yangtze River, which runs west to east across what is now China,” Sacks said.

“While dogs in other parts of Eurasia continued to readily interbreed with wolves, the dogs that moved into Southeast Asia no longer lived near wolves, and so they developed a totally different evolutionary trajectory, influenced by the agriculture of Southeast Asia,” he said. “Those ancient dogs apparently underwent a significant evolutionary transformation in southern China that enabled them to demographically dominate and largely replace earlier western forms.”