Ancient humans made dogs their best friend not once but twice, by domesticating two separate populations of wolves far apart in Europe and Asia.
Scientists on Thursday said present-day genomes reveal a deep internal split between dogs from opposite ends of the Eurasian continent.
At one end lie a large group of closely related European breeds such as the black Labrador, dachshund and pit bull terrier, and at the other are dogs that include the Siberian husky, shar-pei and Tibetan mastiff.