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The cross-breeding of dogs has made it difficult to trace the genetic roots of today's pets, according to a study.

Scientists from Durham and Aberdeen analysed data from the genetic make-up of modern dogs while assessing the archaeological record of dog remains.

They found that modern breeds genetically have little in common with their ancient ancestors.

The scientists believe their research could offer new insights into dog domestication and its evolution.

The findings were published in scientific journal Proceedings of the National Academy of Sciences USA (PNAS).

'Ancient' breeds

Lead author Dr Greger Larson, an evolutionary biologist in Durham University's Department of Archaeology, said: "The study demonstrated that there is still a lot we do not know about the early history of dog domestication including where, when, and how many times it took place.

He added: "We really love our dogs and they have accompanied us across every continent.

"Ironically, the ubiquity of dogs, combined with their deep history, has obscured their origins and made it difficult for us to know how dogs became the first domestic animal.

"All dogs have undergone significant amounts of cross-breeding to the point that we have not yet been able to trace all the way back to their very first ancestors."

According to researchers, while many modern pets may look like those depicted in ancient Egyptian tombs or Roman mosaics, extensive cross-breeding through thousands of years has meant that no modern dog breeds can be truly classified as "ancient".

The study found that the so-called "ancient" breeds such as the Akita, Afghan Hound and Chinese Shar-Pei, are no closer to the first domestic dogs than any other breeds due to the effects of lots of cross-breeding.

Prof Keith Dobney from the Archaeology Department at the University of Aberdeen said: "We still have some way to go to understand how, where and when the dog became man's best friend."