Dogs tap into human bonding system to get close to our hearts

Exchanging gazes with dogs boosts levels of a bonding hormone in both
them and us, suggesting they evolved to hijack a uniquely human way of

April 16th – Ever felt hopelessly bonded to your pooch when it
stares at you lovingly? It turns out that man’s best friend may have
hijacked a uniquely human bonding mechanism, ensuring that we love and
care for it.

Knock-on chemical and behavioural effects
occur when humans bond: eye contact leads to release of the “love
hormone” oxytocin, which elicits caring behaviour, and this in turn
causes the release of more oxytocin. This loop has been shown to be important for human bonding, for example between mothers and their children.

Oxytocin bonding occurs in other mammals,
too, but humans were thought to be unique in using eye contact as part
of this cycle. “Facing others is a threatening behaviour in other
animals,” says Miho Nagasawa at Azabu University in Japan.

But when she and her colleagues got a bunch of dog owners to gaze into their pets’ eyes, they found that oxytocin levels rose not just in the humans – but in the pooches too.

In contrast, when Nagasawa’s team tested
hand-reared wolves, they found no such effect, and wolves spent little
time gazing into their owners’ eyes.

They then sprayed either oxytocin or a
placebo into 27 dogs’ noses, in a randomised experiment. Female dogs
that received the hormone spent more time staring longingly at their
owners, and oxytocin levels also rose in those people.

This means that the tendency to gaze into
eyes must have evolved during the domestication of dogs, says Nagasawa.
She adds that it’s the first demonstrated case of convergent evolution
in cognitive traits between a human and another species.

The only hitch was that although both male
and female dogs – and their owners – received an oxytocin boost from
eye contact, male dogs didn’t spend more time looking at their owners’
eyes when they were sprayed with the hormone.

Nagasawa suggests that this could be because among males oxytocin is known to increase hostility towards members of other groups, so the sprays might have made the male dogs more vigilant about strangers in the room during the experiment.        

Pat Shipman
at Penn State University in University Park has argued that the
co-evolution of dogs and humans – possibly starting as long as 36,000
years ago – gave humans the edge over Neanderthals.

“I had predicted that both domestic dogs
and humans would show adaptations to enhanced non-verbal communication,
but I had not thought of the oxytocin link,” she says. “As the first
species to be domesticated, dogs have a very ancient and very profound
link to humans that affected both of us.”

But not everyone is convinced this shows that dogs evolved to hijack our bonding mechanism through staring into our eyes.

Jessica Oliva
at Monash University in Melbourne, Australia, agrees that oxytocin was
key to the evolution of dogs from wolves, allowing them to bond with
humans. But she thinks that the eye-gazing behaviour could be learned
rather than having evolved over time. “It could be a conditioning
thing,” she suggests.

Clive Wynne
of Arizona State University in Tempe agrees. He says that wolves he
works with do make eye contact if they’ve been brought up in close
contact with people. “I’m questioning the attempt to interpret these
results as an evolutionary process,” says Wynne.

Nagasawa agrees that wolves and other
animals can learn to make eye contact, but says it comes easier to dogs.
And to her, that suggests the behaviour has evolved.

She says this might just be the tip of the
iceberg, too. Next, she wants to study whether dogs feel empathy with
humans. “Most dog owners say when they feel sad, their dogs feel sad
too. And when the owners feel happy, maybe the dogs feel happy too. So
maybe the dogs are very sensitive to the owners’ feelings,” she says.

Read the full study here: “Oxytocin-gaze positive loop and the coevolution of human-dog bonds



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