In the late 1970s, archaeologists made a stunning find in northern Israel. In a 12,000-year-old village, where families buried loved ones under their homes, they uncovered the remains of a woman and a young dog, her hand resting on the puppy’s chest.
The find is some of the earliest evidence of the bond between humans and our canine pals, perhaps the most powerful emotional connection between species in the animal kingdom. But even after years of study researchers are divided on how this bond began. Did it arise over thousands of years, as early dogs became tamer and more attuned to human behaviors? Or was this fire already burning in the ancestors of dogs: the gray wolf?
A new study of young wolves suggests they are indeed capable of making doglike attachments to people. Under some circumstances, they might even view humans as a source of comfort and protection.
The findings add support to the idea that wolves may harbor some traits once thought exclusive to dogs, says Monique Udell, a human-animal interaction researcher at Oregon State University, Corvallis, who was not involved with the work. But other experts say the study was not well designed and therefore is not convincing.
The new work utilizes an experiment known as the Strange Situation test. Originally created to study attachment between human infants and their mothers, it measures how the stress of being confronted with an unfamiliar person or setting changes a subject’s behavior when they’re reunited with their caregiver. More interaction implies a tighter bond.
Wolves aren’t born wanting to participate in such experiments, so the team behind the new study had to do some heavy coddling early on. Christina Hansen Wheat, a behavioral ecologist at Stockholm University, and colleagues hand-raised 10 gray wolves from the time they were 10 days old, before they could even open their eyes. The researchers took shifts, spending 24 hours a day with the pups, initially getting up every 2 to 3 hours in the middle of the night to bottle feed them. (“It was like having 10 newborns at once,” Hansen Wheat says.)
When the animals were 23 weeks old, a caregiver led them one at a time into a mostly empty room. Over the course of several minutes, the caregiver exited and entered the room, sometimes leaving the wolf alone, sometimes leaving it with a complete stranger. The team repeated the experiment with 12 23-week-old Alaskan huskies, which they’d raised similarly since puppyhood.
For the most part, the scientists saw few differences between the wolves and the dogs. When their caregiver entered the room, both species scored 4.6 on a five-point scale of “greeting behavior”—a desire to be around the human. When the stranger entered, dog greeting behavior dropped to 4.2 and wolf to 3.5, on average, suggesting both animals made a distinction between the person they knew and the one they didn’t, the team reports today in Ecology and Evolution. It’s this distinction that the team counts as a sign of attachment.
Dogs and wolves were also similar in making more physical contact with their caregivers than strangers during the experiment.
In addition, dogs barely paced–a sign of stress—during the test, whereas wolves paced at least part of the time. That’s not surprising, Udell says, as even hand-raised wolves are more jittery around people. “The wolves are acting like you would expect wolves to act.”
However, the wolves stopped pacing almost entirely when a stranger left the room and their caretaker returned. Hansen Wheat says that’s never been seen before in wolves. It could be a sign, she says, that the animals view the humans who raised them as a “social buffer”–a source of comfort and support.
For Udell, that’s the most interesting part of the study. “If this is true, this sort of attachment is not what separates dogs from wolves,” she says. In other words, it didn’t have to be bred into them by humans, but could have been favored by human selection.
She speculates that the pacing experiment may imply that other wild animals could form strong bonds with humans. Does that hand-raised cheetah at the zoo view its caregiver as just a food dispenser, or a comforter, she wonders. “These relationships may be happening even when we’re not aware of them.”
Not everyone is convinced. Márta Gácsi, an ethologist at Eötvös Loránd University who helped pioneer the Strange Situation test for dogs and wolves in 2005, says the results don’t match what her team has seen. She and colleagues observed stark differences between wolves and dogs, with the wolves making little distinction between their caregiver and a complete stranger. Based on such results, she and others have concluded that the ability to form attachments with specific humans was not present in wolves.
Gácsi contends there are several methodological problems with the new study, including that the experiment room was familiar to the animals (and thus not “strange” enough to them to elicit an attachment response), that all dogs came from the same breed (making it hard to generalize how wolves compare with dogs in general), and that the wolves didn’t pace enough to say anything about what this behavior means. “I’m afraid no valid conclusions can be drawn” about the study, she says.
Hansen Wheat says she’s not arguing that dogs and wolves are the same. “We’re still talking about wild animals,” she says. “What we saw does not make them dogs.”
But she argues that even picking up hints of bonding behavior in wolves suggests they already had this trait in the early days of dog evolution. “That could have been the seed we selected for,” and then strengthened over the eons, she says. (Something similar may have happened with dogs’ ability to fetch.)
Hansen Wheat says the key to understanding what happened during dog domestication is to pay attention to what they have in common. “I often get asked how wolves and dogs differ—but the real question we should ask is, ‘How are they similar?’” she says. “That’s the key to figuring out how we created the dog.”
