How Dogs Steal Our Hearts

If you consider your dog as your beloved "fur baby," recent scientific research has some heart-warming news to share. Ground-breaking findings reveal that when our canine companions gaze into our eyes, they trigger a remarkable hormonal response akin to the bond between humans and infants. This study, marking the first time such a cross-species hormonal connection has been documented, offers insight into the profound relationship that has evolved between humans and dogs over thousands of years.

"It's an astonishing discovery that suggests dogs have managed to tap into the human bonding system," says Brian Hare, a canine cognition expert at Duke University in Durham, North Carolina, who was not part of the study. Hare believes that this revelation could shed light on why service dogs play a vital role in assisting individuals with conditions like autism and post-traumatic stress disorder. He emphasises the need for further research to validate this discovery due to its far-reaching implications.

Dogs have long been celebrated for their remarkable ability to connect with humans on a deep level. It's not just about walks in the park or their Frisbee-catching skills; dogs comprehend us in a way that sets them apart from other animals. Point at an object, and your dog will follow your gesture, intuitively understanding your intentions, a skill that even eludes our closest relatives, chimpanzees. Furthermore, the mutual gaze between humans and dogs during interactions signifies a level of understanding and affection, a stark contrast to how dogs' closest relatives, wolves, interpret such eye contact as hostility.

It was this shared gaze that piqued the curiosity of Takefumi Kikusui, an animal behaviourist at Azabu University in Sagamihara, Japan. Kikusui's research primarily focusses on oxytocin, a hormone associated with maternal bonding, trust, and altruism. Previous studies have demonstrated that when a mother gazes into her baby's eyes, the infant's oxytocin levels surge, prompting the baby to reciprocate the gaze, which, in turn, increases the mother's oxytocin levels. This positive feedback loop fosters a deep emotional bond between mother and child, particularly during a stage when the infant can't express itself in other ways.

Kikusui, a devoted dog owner for over 15 years, couldn't help but wonder if the same mechanism applied to canines. He shares, "I love my dogs, and I've always felt that they're more like partners than pets. So I started pondering, 'Why are they so closely connected to humans?'"

Kikusui and his team invited 30 of their friends and neighbours to bring their beloved pets to his laboratory. They also reached out to a few individuals who were raising wolves as pets. In their experiment, they collected urine samples from both the owners and their animals before asking them to spend 30 minutes interacting in a room together. During this time, the owners engaged in petting and conversation with their animals, and, notably, both dogs and owners gazed into each other's eyes. The profound impact of mutual gazing became evident in the results.

Amongst the pairs that spent the most time gazing into each other's eyes, both male and female dogs exhibited a remarkable 130% increase in oxytocin levels. Simultaneously, both male and female owners experienced a staggering 300% rise in their oxytocin levels. The study showed no oxytocin increase in cases where there was minimal eye contact between dogs and their owners or amongst the wolf-owner pairs.

In a subsequent experiment, the team repeated the same procedure, this time providing female dogs with a nasal spray of oxytocin before interacting with their owners, excluding the wolves. Female dogs given the oxytocin nasal spray spent 150% more time gazing into their owners' eyes, resulting in a 300% increase in their owners' oxytocin levels. There was no such effect seen in male dogs or in dogs given a nasal spray containing only saline.

These results imply that human-dog interactions trigger a similar oxytocin-driven positive feedback loop to that observed between mothers and infants. This mechanism may explain the profound bond that exists between dogs and humans. Kikusui suggests that the nasal spray's impact may have been limited to female dogs due to oxytocin's more prominent role in female reproduction, particularly during labour and lactation.

Kikusui proposes that this positive feedback loop might have played a pivotal role in the domestication of dogs. As wolves gradually evolved into dogs, those that could form bonds with humans would have received care and protection. In response, humans may have developed the ability to reciprocate, adapting the maternal bonding feedback loop to a new species. Kikusui speculates that this adaptation might have been crucial for human survival, as oxytocin helps reduce anxiety, thus benefiting overall health.

Jessica Oliva, a Ph.D. student at Monash University in Melbourne, Australia, who has researched oxytocin's impact on dogs' ability to understand human gestures, also believes that oxytocin played a role in the domestication of dogs. She acknowledges that mutual gazing doesn't happen in isolation; many dogs associate this behaviour with food and play, both of which can boost oxytocin levels. While we might see our dogs as our babies, it's possible that they view us as cherished companions who occasionally provide them with a comforting massage.

For more on the origin of the human-dog bond, check out a story in Science about solving the mystery of canine domestication.