In the story of how the dog came in from the cold and onto our sofas, we tend to give ourselves a little too much credit. The most common assumption is that some hunter-gatherer with a soft spot for cuteness found some wolf puppies and adopted them. Over time, these tamed wolves would have shown their prowess at hunting, so humans kept them around the campfire until they evolved into dogs. (See "How to Build a Dog.")

But when we look back at our relationship with wolves throughout history, this doesn't really make sense. For one thing, the wolf was domesticated at a time when modern humans were not very tolerant of carnivorous competitors. In fact, after modern humans arrived in Europe around 43,000 years ago, they pretty much wiped out every large carnivore that existed, including saber-toothed cats and giant hyenas. The fossil record doesn't reveal whether these large carnivores starved to death because modern humans took most of the meat or whether humans picked them off on purpose. Either way, most of the Ice Age bestiary went extinct.

The hunting hypothesis, that humans used wolves to hunt, doesn't hold up either. Humans were already successful hunters without wolves, more successful than every other large carnivore. Wolves eat a lot of meat, as much as one deer per ten wolves every day—a lot for humans to feed or compete against. And anyone who has seen wolves in a feeding frenzy knows that wolves don't like to share.

Humans have a long history of eradicating wolves, rather than trying to adopt them. Over the last few centuries, almost every culture has hunted wolves to extinction. The first written record of the wolf's persecution was in the sixth century B.C. when Solon of Athens offered a bounty for every wolf killed. The last wolf was killed in England in the 16th century under the order of Henry VII. In Scotland, the forested landscape made wolves more difficult to kill. In response, the Scots burned the forests. North American wolves were not much better off. By 1930, there was not a wolf left in the 48 contiguous states of America. (See "Wolf Wars.")

If this is a snapshot of our behavior toward wolves over the centuries, it presents one of the most perplexing problems: How was this misunderstood creature tolerated by humans long enough to evolve into the domestic dog?

The short version is that we often think of evolution as being the survival of the fittest, where the strong and the dominant survive and the soft and weak perish. But essentially, far from the survival of the leanest and meanest, the success of dogs comes down to survival of the friendliest. (See "People and Dogs: A Genetic Love Story.")

Most likely, it was wolves that approached us, not the other way around, probably while they were scavenging around garbage dumps on the edge of human settlements. The wolves that were bold but aggressive would have been killed by humans, and so only the ones that were bold and friendly would have been tolerated.

Friendliness caused strange things to happen in the wolves. They started to look different. Domestication gave them splotchy coats, floppy ears, wagging tails. In only several generations, these friendly wolves would have become very distinctive from their more aggressive relatives. But the changes did not just affect their looks. Changes also happened to their psychology. These protodogs evolved the ability to read human gestures.

As dog owners, we take for granted that we can point to a ball or toy and our dog will bound off to get it. But the ability of dogs to read human gestures is remarkable. Even our closest relatives—chimpanzees and bonobos—can't read our gestures as readily as dogs can. Dogs are remarkably similar to human infants in the way they pay attention to us. This ability accounts for the extraordinary communication we have with our dogs. Some dogs are so attuned to their owners that they can read a gesture as subtle as a change in eye direction.

With this new ability, these protodogs were worth knowing. People who had dogs during a hunt would likely have had an advantage over those who didn't. Even today, tribes in Nicaragua depend on dogs to detect prey. Moose hunters in alpine regions bring home 56 percent more prey when they are accompanied by dogs. In the Congo, hunters believe they would starve without their dogs.

Dogs would also have served as a warning system, barking at hostile strangers from neighboring tribes. They could have defended their humans from predators.

And finally, though this is not a pleasant thought, when times were tough, dogs could have served as an emergency food supply. Thousands of years before refrigeration and with no crops to store, hunter-gatherers had no food reserves until the domestication of dogs. In tough times, dogs that were the least efficient hunters might have been sacrificed to save the group or the best hunting dogs. Once humans realized the usefulness of keeping dogs as an emergency food supply, it was not a huge jump to realize plants could be used in a similar way.