The gray wolf.

Over time, the wolves changed in body and temperament.

Their skulls, teeth and paws shrank.

Their ears flopped.

They gained a docile disposition, becoming both less frightening and less fearful.

They turned into dogs.

Scientists agree that all dogs descend from wild ancestral wolves, but they disagree as to when, where and how that happened.

Gregor Larson from the University of Oxford has been trying to get some firm answers.

Already, he and his team have yielded a surprising discovery.

They think dogs were domesticated not once but twice.

So here's the full story as Larson sees it.

Many thousands of years ago, somewhere in western Eurasia, humans domesticated grey wolves.

And the same thing happened independently far away in the East.

Around the Bronze Age, some of the ancient eastern dogs migrated west alongside their human partners.

And along their travels, these migrants encountered the indigenous, ancient western dogs.

They mated with them, doggy style presumably, and effectively replaced them.

So today's western dogs trace most of their ancestry to the ancient eastern migrants.

Less than 10 percent comes from those ancient western dogs, which have since gone extinct.

Other dog genetics experts think that there are other possible explanations.

But Larson adds that his gene-focused peers are ignoring one crucial line of evidence--bones.

If dogs originated just once, there should be a neat gradient of fossils with the oldest ones at the center of domestication and the youngest ones far away from it.

But that's not what we have.

So we now have a new origin story for dogs.

And this matters because dogs were the first species that we domesticated.

They came before crops, before livestock.

They heralded a change in our relationship to the natural world.