Oxytocin, or the love hormone, helps reinforce the bond between a parent and a child. And now, researchers working with man’s best friend reveal that dogs have tapped into—or hijacked, some might say—this same instinctual bonding mechanism. Gazing into those sweet puppy dog eyes increases our oxytocin levels, and theirs too. The findings, published in Science this week, suggest that this “oxytocin-gaze” may have been acquired during the domestication of dogs from wolves.
"I love my dogs, and I always feel that they’re more of a partner than a pet," study leader Takefumi Kikusui of Azabu University tells Science. "So I started wondering, 'Why are they so close to humans? Why are they connected so tightly to us?'" An oxytocin-driven bonding mechanism likely evolved to strengthen emotional ties between humans and their babies. And while the hormone is also found in other mammals, we used to think that we were unique for incorporating eye contact, especially because really young babies can't communicate in that many ways. Not to mention, "facing others is a threatening behavior in other animals," Azabu's Miho Nagasawa tells New Scientist. Well, turns out oxytocin also spikes in both human and dog brains when the two species interact, operating in a positive feedback loop that likely fortified the bonds between us and our pups for thousands of years.
Kikusui, Nagasawa, and colleagues recruited 30 of their friends to let them document every interaction the owners had with their pet dogs—staring, talking, petting—in a room for 30 minutes. They measured oxytocin levels in urine samples collected from both person and pooch right before and right after. The researchers found that sustained eye contact between owners and their furbabies drove up levels of oxytocin in the brains of both: a rise of 130 percent in dogs and 300 percent in people, Science reports. More oxytocin, more love, trust, and nurture.
In another experiment, the researchers sprayed oxytocin into the noses of 27 dogs and placed them in a room with their owners and strangers. Petting was not allowed. In this situation, female dogs spent longer gazing at their owners—which triggered a longer gaze in return from their people, whose oxytocin levels rose within that half hour. Pictured to the right is a standard poodle named Jasmine as she stares at a student. Her gazing behavior significantly increased along with her owner’s urinary oxytocin after the spray was administered. The nasal spray didn't cause male dogs (such as Hook, pictured above) to stare longingly at their owners, and that might be because oxytocin made them more vigilant towards strangers.
This mutual gaze and its oxytocin-mediated feedback loop isn't a response that's found in wolves—not even the ones who were hand-raised as pets by humans. The team thinks that this particular bonding mechanism co-evolved in us and our canine companions-to-be over the course of their domestication. Dogs who bonded with people earned our care; humans who reciprocated had lower anxiety and were likely less stressed thanks to the surge in oxytocin. Nagasawa adds that this is the first demonstration of convergent evolution in cognitive traits between humans and another species.
Images: Mikako Mikura