CROSS-BREEDING has diluted the canine gene pool so much that it is now difficult to trace the genetic roots of the current generation of dogs, scientists from Durham and Aberdeen Universities have concluded.

Scientists compared the make-up of modern dogs with archaeological records of dog remains.The scientific journal Proceedings of the National Academy of Sciences USA (PNAS) has published the findings.

Dr Greger Larson, an evolutionary biologist in Durham University's Department of Archaeology, told BBC News: “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."

The report concludes that extensive cross-breeding through the thousands of years since evidence of the first dogs to populate the earth were found in the Egyptian tombs or Roman mosaics mean that no modern dog breeds can be accurately classified as ancient.