Anyone who has ever loved a dog would find life without our four-legged friends unimaginable. But there is much about the dog's origin that remains a mystery.

Scientists agree that the modern dog evolved from the grey wolf. But there is still controversy as to how and when dogs first became domesticated. Jean Hofve, DVM, and Celeste Yarnell, PhD, write in their book, Paleo Dog, "Canine domestication may have occurred more than once, with many and far-flung groups of wolves. Wandering groups of people and semi-domesticated wolves may have subsequently crossed paths, increasing the genetic diversity as their wolf-dogs interbred."

The results of DNA studies on when dogs split from wolves vary wildly, with estimates ranging from 7,000 to 140,000 years ago. Then there are the archeological findings. During a 2012 dig, researchers digging in a Siberian mountain cave discovered an ancient canine skull they estimated to be 33,000 years old. (Equally ancient remains were found in a cave in Belgium.) The researchers said the Siberian artifact was domesticated because of its short, wide muzzle and crowded teeth. Wolves, in comparison, have long, thin snouts. But Kathryn Lord, PhD, who teaches courses in animal behavior and evolution at Hampshire College in Amherst, Massachusettes, said the findings are not conclusive, as young wolves also have shorter, wider muzzles.

Scholars also disagree about how dogs became domesticated. Some believe early humans took in wolf pups, raised them, and kept them around for hunting. "It's likely that Paleo (Stone Age) humans knew where the wolves' dens were; they could have taken unattended or orphaned cubs to raise by hand," Dr. Hofve explains. "It wouldn't take long to figure out that the friendliest cubs were the best bet. These naturally tamer pups must have been the ancestors of the modern dog. As human beings shifted from being nomadic hunter-gatherers to farmers living in communities, the wolf stayed with them, and in doing so, changed its ways. Selective breeding began, and so developed the domestic dog."

Another theory is that certain wolves were brave enough to visit these agricultural communities to forage for food. "Suddenly, we had garbage dumps, which to this day is very attractive to animals," Lord says. "The wolves that didn't run away got all the best food."
Eventually, most likely, they began following humans around, just like dogs do today, Lord says.

A 40-year experiment carried out by a Russian scientist, Dmitry Belyaev, supports this theory, according to Lord. Belyaev bred 35 generations of wild silver foxes specifically for the trait of tameness. Over time, the foxes not only bonded with their handlers, but also began to look and sound more like dogs. They barked and even developed spotted fur and floppy ears!

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