There’s a scientific reason many of us fall in love with our dogs, and it speaks to the power of puppy dog eyes.

A new study found that when canines look into our eyes, it activates the same hormonal response in us that occurs between human mothers and their offspring, encouraging them to bond.

Researchers posit that this effect explains how dogs became human companions thousands of years ago.

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“The human-dog relationship is exceptional because it is an interspecies form of attachment,” reads the study, published in the research journal Science.

According to the study, gaze plays a critical role in human communication.

“Gaze not only facilitates the understanding of another’s intention but also the establishment of affiliative relationships with others. In humans, ‘mutual gaze’ is the most fundamental manifestation of social attachment between a mother and infant.”

Mutual gaze became the cornerstone of the study, led by Takefumi Kikusui, a dog lover and animal behaviorist at Azabu University in Sagamihara, Japan.

Kikusui studies oxytocin, the so-called “love hormone” responsible for expressing and responding to emotion and strengthening bonds.

Previous studies have established that when a mother and child stare into each other’s eyes, oxytocin levels increase in both parties. This positive feedback loop is the foundation for a deep but largely nonverbal relationship.

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Kikusui surmised that a similar feedback loop might exist between dogs and people.

“I love my dogs, and I always feel that they’re more of a partner than a pet,” he said. “So I started wondering, ‘Why are they so close to humans? Why are they connected so tightly to us?’ “

Kikusui and his team contacted 27 pup parents and a handful of people raising wolves and invited them to participate in the lab-based study.

The research team collected urine samples from both canines and humans and then instructed owners to interact with their animals in a room for 30 minutes. During this time, dogs and their people gazed into each other’s eyes for varying lengths of time, a few seconds to a few minutes.

Wolves were generally less interested in or capable of making eye contact.

At the end of the half-hour session, urine samples were again collected.

Of the dog-human duos that spent the most time gazing into each other’s eyes, the dogs experienced a 130% rise in oxytocin levels, while humans experienced a 300% increase. The team observed no increase in wolf-owner duos or dog-human teams that spent minimal time gazing.

These results suggest that wolves do not use mutual gaze as a form of social communication with humans, as wolves tend to use eye contact as a threat.

In a second experiment, the protocol was repeated but wolves were excluded, and dogs were given a nasal spray of oxytocin before interacting with their owner.

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Female dogs who received the spray spent 150% more time gazing into their owners’ eyes. In response, owners experienced a 300% spike in their oxytocin levels. No effect was recorded in male dogs. Kikusui hypothesizes that the nasal spray may have exclusively affected female dogs because oxytocin plays a more significant role in female reproduction.

According to researchers, these results suggest that human-dog relationships are rooted in the same positive oxytocin feedback loop as mother-infant interactions. This explains why we feel so close to our canine companions and they to us.

Kikusui argues that this feedback loop played a pivotal part in the domestication of dogs. As wolves evolved into dogs, only those who exhibited the ability to bond with humans were offered care and protection.

Kikusui also suggests that because oxytocin decreases anxiety, this feedback loop was and is critical for our well-being. “If human beings are less stressed out, it’s better for their health.”