It's a question that bedevils dog owners the world over: "Is she staring at me because she loves me? Or because she wants another biscuit?"
Research published Thursday in the journal Science suggests that love (or something close) could be behind that stare. The work shows that when dogs and their people gaze into each other's eyes, all get a boost in their circulating levels of oxytocin — a hormone thought to play a role in trust and emotional bonding.
The results suggest that both dogs and people feel it, something few dog owners would doubt.
For thousands of years, humans have bred dogs for obedience, and that has altered their brains as well. For example, MacLean says, dogs are excellent at understanding gestures like pointing. They're also good with language.
But have humans also bred dogs for affection?
"Well, it's a harder one to get at, partially because emotions are so subjective," MacLean says. For instance, many owners say their dog feels guilty after behaving badly, but that's not true.
"There have been good studies to show that, actually, what's happening in those situations is that dogs are ... just responding to people," he says. In other words, the dog looks guilty to you because you look angry to the dog.
A team led by Takefumi Kikusui, at Azabu University's school of veterinary medicine in Japan, has now found a more quantitative measure of emotion. The scientists let owners and dogs interact. And rather than just watching each pair, the team took urine samples from the people and the dogs.
"They measured oxytocin, which is a hormone that has been very associated with trust and social bonds," says MacLean, who was not part of the research team.
Oxytocin is the same bonding hormone thought to give parents warm fuzzies when looking at their infants.
Researchers found that when dogs stared into their owner's eyes, oxytocin levels rose in both the people and the dogs. The same was not true for wolves, who were observed with their handlers. The team also found that when dogs were given a shot of oxytocin, they would stare into the eyes of their owners for a longer period, and that gazing, in turn, would boost the oxytocin levels in the owners. That increase points to a hormonal feedback loop between the dogs and the humans.
Taken together, MacLean says, the findings suggest a special bond between dogs and people — a bond that may have evolved as humans bred them. "I'm perfectly happy saying that we can love dogs, and they can love us back," MacClean says, "and oxytocin is probably a piece of how that happens."
But not everyone is buying this hormonal connection.
"There is a fashion in science at the moment, to identify changes in hormone levels with changes in emotional and feeling states," says Clive Wynne, a psychologist at Arizona State University who studies how dogs and people interact.
In fact, oxytocin is not always associated with love, he points out. The hormone can also be linked to feelings of emotional isolation — even aggression in some animals. The wolves used in the study didn't make a lot of eye contact, Wynne says. If they had, their oxytocin might have gone up too.
But Wynne adds that, oxytocin or no, he believes the bonds between dogs and humans are real.
"I think the best evidence that any dog lover has that their dog loves them is what the dog does was when it's around them," Wynne says. "We're entitled to trust the evidence of our own senses."
ROBERT SIEGEL, HOST:
If you're a dog owner, this question has probably crossed your mind. Is she staring at me because she loves me or because she wants another biscuit? Well, new research out today in the journal Science may provide some clues. NPR's Geoff Brumfiel has this report on puppy love.
GEOFF BRUMFIEL, BYLINE: Just up the street from NPR's headquarters, I found Myrna Charles walking her Great Danes.
MYRNA CHARLES: This is Peace and Quiet. This one's Quiet. Quiet, you going to say hi?
BRUMFIEL: Peace and Quiet are a lot of dog to handle.
CHARLES: He's 185 pounds, and she's 140 pounds.
BRUMFIEL: But they're also nice doggies.
CHARLES: They're pretty good. The only time they run is really if there's a squirrel.
BRUMFIEL: And what do you do when there's a squirrel?
CHARLES: I let the leash go because if not, I'm in a tree or I'm being dragged with them.
BRUMFIEL: Part of the reason Peace and Quiet are so well behaved is because of domestication. For thousands of years, humans have bred dogs for obedience, but what about affection?
EVAN MACLEAN: Well, it's a harder one to get at partly because emotions are so subjective.
BRUMFIEL: Evan Maclean is at Duke University's Canine Cognition Center. He says sometimes humans project emotions.
MACLEAN: I think a common one is that people always talk about dogs looking guilty. You know, you come home from work, and there's a mess in the house, and you look at your dog, and you knew they were feeling guilty about what they did. And, you know, there have been good studies to show that actually what's happening in those situations are dogs are actually just responding to people.
BRUMFIEL: The dog looks guiltily at you because you look angrily at the dog. A team at Azabu University in Japan has now found a more quantitative measure of emotion. They let owners and dogs interact and rather than just watching them, the team took urine samples.
MACLEAN: And what they did is they measured oxytocin, which is a hormone that has been very associated with trust and social bonds.
BRUMFIEL: Oxytocin is the same bonding hormone that gives parents warm fuzzies when looking at their infants. Researchers found that when dogs stared into their owners eyes, oxytocin levels rose in both the people and the dogs. The same was not true for wolves who were observed with their handlers.
MACLEAN: That suggests that what they observed in dogs might actually be something special about dogs and not just a general feature of interaction between humans and any other animal.
BRUMFIEL: Now, not everyone is buying this hormonal connection. Clive Wynne is a psychologist at Arizona State University who studies how dogs and people interact.
CLIVE WYNNE: There is a fashion in science at the moment to identify changes in hormone levels with changes in emotional and feeling state.
BRUMFIEL: In fact, oxytocin is not always associated with love. The hormone can also be linked to feelings of emotional isolation, even aggression in some animals. And Wynne says the wolves didn't make a lot of eye contact. If they had, their oxytocin might have gone up, too. But honestly, Wynne believes dog owners shouldn't worry.
WYNNE: I think the best evidence that any dog lover has that their dog loves them is what the dog does when it's around them.
CHARLES: No, no.
BRUMFIEL: Back outside, a passing doggy gets Peace and Quiet excited. Owner Myrna Charles settles them down, then she tells me she's got no doubt about their love for her.
CHARLES: Look at his eyes. You're not even his owner. Look at his eyes. Wouldn't you like - oxytocin levels - oxytocin levels.
BRUMFIEL: Geoff Brumfiel, NPR News. Transcript provided by NPR, Copyright NPR.