Megan Callahan-Beckel has been working with gray wolves since she was 4 years old. Now the animal care coordinator at the Wildlife Science Center in Minnesota—where her mother, Peggy Callahan, is the executive director—Callahan-Beckel grew up in a home inhabited by not only dogs but also wolf puppies, who must be intensively hand-reared for them to be comfortable with humans later in life. She now raises wolf puppies in her own home every summer, and they come to adore her and see her as a kind of mom.
Much as she loves the wolves, Callahan-Beckel is well equipped to explain why dogs live in our homes and wolves stick to the great outdoors. “They test you, they get into your face, they are cocky, they’re destructive,” she says. “They’re everything that people shouldn’t want in dogs.”
For scientists who want to understand how dogs came to be our constant companions, this contrast presents a promising path forward. While wolves and domestic dogs technically belong to the same species—they can interbreed and produce fertile offspring—their genomes hold meaningful differences. Unlike wolves, for example, dogs are omnivorous: Over the tens of thousands of years that dogs have lived alongside humans, they have evolved to produce larger amounts of an enzyme needed to digest carbohydrates. (House pets can lead long and healthy lives on a kibble diet.)
But the dog-human bond is more than a matter of a digestive protein—it comes down to behavior. “We’re interested in what makes dogs special,” says Clive Wynne, director of the Canine Science Collaboratory at Arizona State University. “How is it that dogs have the amazing role in our lives that they do, and that they have had for thousands of years? How do they pull that off?”
To answer this question, researchers can directly compare the behavior of dogs and wolves to figure out what has changed since their evolutionary divergence. Over five years of testing at the Wildlife Science Center, a team led by Brian Hare, director of the Duke Canine Cognition Center, managed to obtain behavioral data from 37 hand-reared wolf puppies—a far larger sample than anyone had previously tested. They compared the results from wolves with data from 44 dog puppies, who had been raised in litters and so had less human contact than many pet dogs do, and found that the dogs were much more interested in—and better at communicating with—people, despite their comparatively low level of human interaction. Their results were published in July in the journal Current Biology.
The dog and wolf puppies displayed their communication skills by completing a food-finding task with a human partner. The experimenter hid food in one of two bowls, and then pointed to the bowl with the snack or placed a colored block beside it. Unlike a dog who sits in response to a verbal command from its owner, these puppies had never been trained to use the nonverbal cues—the experiment was designed to get at their innate ability to respond to human gestures and signals. While the wolf puppies showed some limited ability to complete this pointing task, the dog puppies performed far better in both versions of the experiment. On both tests, the dogs chose the correct container more than three out of four times; the wolves’ success rate was closer to 60 percent.
Researchers have known for a long time that dogs are particularly good at this pointing task. They even appear to be better at it than chimpanzees, who are otherwise thought to be substantially more intelligent. But this observation alone doesn’t necessarily explain what’s going on with dogs. Perhaps they spend more time around people and so learn more about human gestures, or perhaps their abilities have a genetic root.
Earlier this year, researchers found new support for this second idea when they measured the extent to which the ability to follow pointing gestures runs in dog families. Puppies who were more closely related to each other scored more similarly on the pointing test, which indicates that their scores could be partly explained by their genetics.
The ability of dogs to complete this task could be a product of domestication. Humans, intentionally or unintentionally, could have prompted dogs to become more effective communicators; people could have purposefully bred the friendliest dogs with each other, or, alternatively, the friendliest individuals could have been the most successful at living with humans. Or, the ability could be inherited from the common ancestor of dogs and modern-day wolves. To distinguish between these two possibilities, and to limit the influence of environmental factors, researchers have tried to compare dog and wolf puppies who were raised similarly. A 2008 study found that the dogs did better than the wolves on the pointing task, but a paper published the following year failed to replicate that difference.
This new study, which has a far larger sample size and compares wolves with more human contact to dogs with less contact, solidifies the conclusion that dogs are indeed better at this task than wolves, says Juliane Bräuer, head of the DogStudies Lab at the Max Planck Institute for the Science of Human History. “It was quite a big sample size, especially for the wolves,” she says. “To find testable wolves is always a challenge.”
Dogs’ abilities to follow pointing cues, then, appear to be a product of domestication—there’s an important genetic difference between dogs and wolves at work here. But just where genetics enters the picture remains an open question. Hare thinks that the key element is an evolved reduction in the natural fear that wolves have toward humans. (“Wolves are giant wusses,” Callahan-Beckel says.) As pack hunters, wolves need to be capable of coordinating with other members of their species. Hare believes that, during the process of domestication, dogs expanded their potential set of coordination partners to include people. “Dogs inherited a skill set at understanding others from wolves,” he says. “When fear was replaced by an attraction, those skills became enhanced.”
But perhaps dogs are simply more inclined to learn from humans, and do so incredibly quickly. In support of this second possibility, Wynne notes that the older dog puppies in the study performed better on the pointing task than the younger ones, which suggests that some learning was taking place.
In general, Wynne finds it difficult to believe that dogs have an ingrained ability to understand human gestures or human intentions. “It’s just absurdly unlikely that dogs could be born with an innate ability to follow human pointing gestures, when our own children are not born with an ability to follow human pointing gestures,” he says.
Both Hare and Wynne agree, however, that there is one major, striking difference between dogs and wolves, regardless of how they are raised: Dogs are far, far more attracted to humans. The wolves that Callahan-Beckel and Callahan raise will often, as adults, let their rearers rub their bellies and scratch them behind the ears. Strange humans, however, are a different story. In the study, dog puppies were 30 times more likely to touch unfamiliar humans than wolf puppies were.
Some wolves will see Callahan-Beckel and Callahan as their moms for life and greet them the way a pet dog might greet its owner arriving home from work. But others reveal their genetic history when they ultimately come to view their rearers as a leader to be overthrown. This happened recently for Callahan-Beckel, when Adam, a wolf she had raised, became the leader of his pack—and then decided he was the boss of her as well.
“I still love Adam. I still love him so much,” Callahan-Beckel says. “And I walk up to the fence [saying], ‘Oh, Adam, that’s my good boy,’ and he hits the fence as hard as he can, roaring, with his tail up, trying to kill me. And it’s just the way they are.”