The Chemical Behind Those Puppy Dog Eyes

Japanese study finds that both dogs and their human companions release a 'love hormone' into the blood when looking at each other.

Reuters

The loving gazes that dogs bestow on humans are anything but coincidental, according to new research conducted in Japan.

In fact, dogs may have become domesticated in part by adapting to a primary human means of contact: eye-to-eye communication, according to the research. 

And both the dog with the "you are everything to me" gaze and the human on the receiving end are flooded with oxytocin, the hormone of love, nurture, mutual trust and, above all, bonding that forms between a parent and child.

The study, conducted by researchers at Azabu University, Jichi Medical University and the University of Tokyo Health Sciences, all in Japan, was published in Science magazine on Thursday and reported by the New York Times.

By observing the interactions of 30 dog owners and their canine companions, the researchers found that the amount of oxytocin produced by both human and pet increased the more they gazed into each other's eyes.

When the dogs were given a supplemental dose of oxytocin prior to their interaction with the humans, the increased oxytocin boosted the number of times that female dogs locked eyes with their owners, leading to an increase in oxytocin released in the owner's blood. But the same response was not noted in male dogs.

Neither the locked eyes nor the surge in oxytocin were observed in similar tests with wolves.

Unlike dogs, wolves “tend to use eye contact as a threat” and are inclined to “avoid human eye contact,” wrote Miho Nagasawa, a research fellow at Jichi Medical University and one of the authors of the study.

Dr. Takefumi Kikusui, a professor in the School of Veterinary Medicine at Azabu University, added that he believes that the differences in gaze between dogs and wolves means “that dogs have acquired this superior ability during the evolutionary and domestication process of living with humans.”

“There is a possibility that dogs cleverly and unknowingly utilized a natural system meant for bonding a parent with his or her child," he added.

The changes in oxytocin were most pronounced in dogs who fixed longer gazes on their owners, which researchers defined as 100 seconds in the first five minutes of the encounter. They saw no significant difference in oxytocin levels among the breeds or sex of the dogs participating in the study.

The study's results suggest that dogs and humans grow to love and protect each other through a positive-feedback loop that is mediated by the same neurochemical – oxytocin – that jump-starts the bond between infant and mother, that cements mutual trust between lovers, and that transforms men from solitary hunters to loving protectors of their families.

Other experts on canine behavior expressed caution about overstating the implications of this study.

“We don’t know what the dog’s gaze means," said Evan L. MacLean, co-director of the Duke Canine Cognition Center and a co-author of a commentary accompanying the study. "When you look at a human baby, it feels good. Maybe dogs gaze at you because it feels good. Maybe the dogs are hugging you with their eyes?"

Dogs may stare fixedly at humans because, for dogs, human behavior is “the telltale of everything that is about to happen,” Dr. MacLean said.