An analysis of the genetic make-up of modern-day dogs found that modern breeds genetically have little in common with their ancient ancestors, Britain's Durham University reported Monday.
That makes it extremely difficult to trace the ancient genetic roots of today's pets, researchers said.
While many modern breeds look like those depicted in ancient texts or drawings, millennia of cross-breeding means it is inaccurate to label any modern breeds as "ancient," they said.
Breeds such as the Akita, Afghan Hound and Chinese Shar-Pei, often classed as "ancient," are no closer to the first domestic dogs than other breeds, genetics studies have found.
This makes it difficult to determine the early history of dog domestication including where, when, and how many times it took place, researchers said.
"We really love our dogs and they have accompanied us across every continent," Durham evolutionary biologist Gregor Larsen said.
"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 man's best friend.
"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."