The genome of an ancient dog, described in a new study, informs upon the demography and domestication of man's best friend. How wolves became the canine companions of today has remained controversial, both in terms of the number of times dogs evolved, as well as just where this evolution occurred. A number of genetically-based studies have concluded that dogs were probably domesticated just once, yet the scientific community continues to debate whether this occurred in Europe, Central Asia, or East Asia. From where and when then, did man's best friend originate? To gain even greater insights into the prehistoric pattern of dog domestication, Laurent Frantz analyzed 59 mitochondrial DNA sequences from ancient European dogs that lived between 14,000 to 3,000 years ago, as well as a comprehensive genome of an ancient Newgrange (Irish) dog that lived roughly 4,800 years ago, comparing these genetic data to the full genome sequences of hundreds of modern wolves and dogs of different breeds from Western Eurasia and East Asia. Their analyses reveal a deep split between dogs from the two regions - one they say occurred several millennia after the first known appearance of dogs in Europe and East Asia. While the researchers do not rule out the possibility of a single origin of Eurasian dogs followed by early transportation to Europe, they emphasize that a lack of archeological evidence of dogs between the two regions supports two independent dog domestication events. Some species, such as the Greenland sledge dog or Siberian husky, appear to possess mixed ancestry from both Western Eurasian and East Asian dog lineages, the authors say.