The story ends with a dog curled up at the foot of a bed, having been fed and patted by its owner. But exactly how the canine-human relationship began is a mystery. When and where were dogs first domesticated? For what purpose? How different are they from their fiercer canine relatives, the wolves?
Some clues can be gleaned from dogs and wolves themselves, as well as from fossils of early canids. And in the last decade or so, genetic data have come into play. A 2002 study showed that the greatest genetic diversity in living dogs and wolves (as measured in the mitochondrial genome and later in the Y chromosome) exists in southern East Asia. That led some to finger that region as the birthplace of dogs. But a 2010 study, which used a different kind of genetic analysis to look at 48,000 gene markers in living animals, suggested a close relationship between dogs and Middle Eastern wolves.
A new study, reported by molecular biology writer Tina Hesman Saey, offers a third option — Europe. An analysis of mitochondrial DNA taken from ancient doglike and wolflike fossils shows that living dog species are most closely related to a line of wolves that once roamed Europe. Scientists estimate that dogs emerged as a distinct subspecies more than 18,000 years ago, before the dawn of farming. Which gets us to the question of just why and how dogs first became human companions. If dogs were domesticated by hunter-gatherers, they might have been bred to aid in hunting, for example.
Speaking at the New Horizons in Science meeting on November 3, Clive D.L. Wynne had another idea about how dogs originated. Wynne, a psychologist at Arizona State University in Tempe, thinks it was not initially a human-driven process. Instead, he proposes that dog ancestors started out as scavengers at human trash heaps. Lured by an easy meal, the dogs may have wandered closer and closer to humans. These people might have seen dogs’ utility — perhaps as lookouts with an intimidating bark. Dogs might also have been valued as a source of protein. Random genetic changes may have helped increase mutual toleration between the species. One gene mutation found in dogs but not wolves also turns up in people with a disorder marked by an outgoing and friendly personality, Wynne said. This might have enabled dogs to help on the hunt, and eventually led to interspecies affection.
Wynne is openly speculating. But that’s OK. To get to the bottom of the story we’ll need to use all the clues we have, plus a healthy dose of imagination.