The Genetics of Why You and Your Dog Are in Love

Mutation related to the bonding hormone oxytocin had been assumed to lie behind the extraordinary bond that emerged between human and hound. Guess again

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A Jack Russell Terrier. Pleased to see you.
A Jack Russell Terrier. Pleased to see you.Credit: Javier Brosch/
Ruth Schuster
Ruth Schuster
Ruth Schuster
Ruth Schuster

You love your dog. Your dog loves you. Your love is the upshot of thousands of years – perhaps tens of thousands of years – of doggie domestication, during which people apparently selected canines for amiability, tractability and smarts. A few eccentrics might have chosen snarling monsters, but we assume that prehistoric people generally chose nice animals that demonstrated comprehension of the humans’ gestures; somebody happy they came back to the cave, rather than reacting with avoidance and horror and/or appetite.

They also likely didn’t tend to adopt nervous wrecks, it now appears.

Much work has been done on the role played by the dog’s facial musculature, et cetera. Now a new paper in Nature journal Scientific Reports by Akiko Tonoike and Miho Nagasawa of central Japan’s Azabu University with colleagues focuses on genetic aspects of doggo domestication.

A woman kissing her dog during a "kissing flashmob" in celebration of Valentine's Day, in ParisCredit: Thibault Camus / AP

The team looked at variations in four genes known to be involved in sociability, to see if they differed in wild and tame (to overstate the case) dogs:

1. Melanocortin-2 receptors, aka MC2R, which is involved in production of the stress hormone cortisol.

2. Oxytocin, the “bonding hormone.”

3. Oxytocin receptors.

4. WBSCR17, which is involved in Williams-Buren syndrome in humans, which involves hyper-social behavior.

They did find differences, and let us take a sneak peek at one conclusion. The less genetically prone to stress the canine is, the more agreeable it would have been to human attention, enabling the animals to stop going bonkers and to look deep into your eyes.

In fact, it has been suggested that reduced stress responsiveness in the wild dog was the start of domestication, says co-author Nagasawa.

Note that the team didn’t directly measure cortisol in the dogs but will be doing so, she adds. But they found an association between specific genetic variations and social behavior in our friend the dog.

Children playing with a dog in the war-ravaged neighborhood of Bucha, on the outskirts of Kyiv, Ukraine, in April.Credit: Rodrigo Abd /AP

Look into my eyes, Fifi

The role of the dog’s facial musculature, enabling it to wiggle its eyebrows in appealing ways that wolves largely cannot do, has been discussed. So has the potential role of prehistoric meal scraps in dog domestication. Eyebrow management boils down to communication, and communication must have been key.

This study began with quantifying how well 624 domestic dogs understand human gestures and communication. The dogs were of two basic types: “ancient” Japanese breeds like the Akita, which are genetically closer to wolves; and general European breeds more distant from the wolf.

Why only Japanese dogs? Why scorn the husky, the malamute? “Genetic analysis by Parker et al shows that Japanese dogs (Shiba and Akita canines) belong to a group that is genetically closest to wolves,” Nagasawa answers. All the dogs in the analysis live with humans, but to represent ancient dogs they chose conveniently accessible ones.

The team doesn’t purport to pinpoint the genetics of dog domestication, but light is being shed.

The dogs were given two tasks, both depending on understanding human gestures and communication.

One involved deducing which bowl was hiding food underneath based on a human gazing at the appropriate bowl, pointing at it and tapping it. This tested the dogs’ understanding of our cues, the team explains. All the dogs performed about the same. (Some cats will also respond to such cues, if they feel like it.)

The second task was unsolvable: trying to open a container with food inside. Here the point was to measure how often the dog looked at the experimenter (“Help!”), and for how long. This tested social attachment to humans, the team explains. It turned out that the "ancient" breeds looked less frequently at the humans compared with the modern dogs.

Moira, an 8-week-old Labrador puppy, giving lots of kisses to her Guiding Eyes for the Blind volunteer, in Maryland earlier this year.Credit: Carolyn Kaster / AP

When Fido freaks

Both tests involved social cognitive skills that exist in dogs but not in wolves: the ability to follow pointing and gestures, the team explains.

And now for a technical moment that shall pass quickly. Two mutations in the MC2R gene were associated with good performance of both tasks.

But variations in the oxytocin gene, its receptor, and the Williams-Buren syndrome gene WBSCR17 affected the dogs’ performance only in the second task. (Nagasawa and colleagues previously demonstrated in 2015 that sniffing oxytocin increases gazing behavior in dogs.)

All of which means what? That the genes influencing the dogs’ performances in the first and second tasks differed. Technical moment over.

When, where and how the dog was domesticated is heatedly argued about – one recent theory being, Siberia 23,000 years ago. There are other theories. Anyway, Tonoike and the team write, the genetics indicate two bottlenecks during the process of their domestication.

One seems to have happened early in their initial transition from wolves to dogs. The second happened with the recent formation of modern dog breeds.

Ergo, even the “ancient” breeds of dog have mad communication skills, suggesting this skill set developed early in the domestication process, before the recent emergence of breeds.

But variants closer to the wolf do not evince strong attachment with their humans, suggesting that attachment behavior was acquired late in the domestication process. Nagasawa points out that dogs may have understood human gestures such as pointing, albeit with differences; the next step may have been upgrading the relationship by our exploitation of this ability.

“Furthermore, the behavior of gazing at humans may have been selected to form a bond between humans and dogs. However, how dogs were used as a working animal, climate, culture, and other factors are thought to have played a major role in this selection,” she says.

Why is cortisol involved? The team focused on cortisol and oxytocin mainly because they inferred that terror and stress in the early canine would not have been conducive to adoption, while a relaxed proto-dog would fare better.

“Cortisol regulation of social tolerance and non-fearful response to humans may have been the most important turning point in the domestication of dogs,” the team writes.

Olga from Bucha holding her dog in a school building, amid Russia's invasion of Ukraine, last month.Credit: STRINGER/REUTERS

Sex and the single dog

Oxytocin is produced in our brains and plays a role in aspects of our socialization. In women it gets released during sex and when giving birth, and when they lactate, and is believed to play a role in bonding with baby.

Men’s brains also release oxytocin, and so do their testicles. What the hormone achieves for their socialization and devotion is still under investigation. In some species male release of oxytocin seems to be related to ejaculation, and the hormone may also be involved in steroid metabolism.

Nagasawa has also previously shown, in the oxytocin-dog paper, that mutual gazing boosts oxytocin in the dog (and us), but not the wolf. “Convergent evolution between humans and dogs may have led to the acquisition of human-like communication modes in dogs,” she wrote, and that could have been a by-product of reduced fear and aggression. But the role of oxytocin in domestication is still under investigation.

What is clear is that we like it when dogs look at us and seem to smile – and we selected for it.

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