Puppy eyes seem to bond humans to canines, and new research shows the look of a dog's eyes hijack the human hormonal system, taking over channels normally used between babies and adults. This new study out of Japan suggests the intense bonds between humans and canines may be fueled by body chemistry.

Oxytocin, sometimes known as "the love hormone," helps to secure emotional connections between adults and babies. Investigators found that this chemical becomes more prevalent in both human and dogs while they are together, suggesting a tie-in between parental bonding and dogs. This effect is even more pronounced when canines and people are gazing into one another's eyes, researchers discovered.

Dogs were placed in a room, along with their owners, as the pair interacted. Researchers then measured oxytocin levels though urine samples. These showed that levels of the hormone increased in both humans and canines, and this effect was greatest in pairs who experienced the greatest amount of eye contact, or gazing.

Researchers placed samples of the hormone inside the noses of dogs and placed them in contact with their owners as well as human strangers. They found eye gazing from female dogs increased under both conditions, but no effect was noted in male animals.

Oxytocin is manufactured in the hypothalamus, an area of the brain that creates several hormones to regulate various body functions. The hormone is then secreted from the pituitary gland, a pea-sized section of brain that controls the functioning of hormone-producing regions of the brain. Oxytocin is released during breast feeding, childbirth and during the course of sexual arousal.

"Oxytocin has many positive impacts on human physiology and psychology," Takefumi Kikusui from Azabu University in Japan said.

Among dogs, oxytocin levels rose 130 percent following gazing, and concentrations in humans increased 300 percent. No rise in oxytocin levels were noted in wolves raised by humans as they interacted with their owners.

An oxytocin feedback loop has also been observed in human babies and mothers. Eye gazing increases oxytocin levels in both mother and child, which drives more staring; this releases more of the trust hormone. This process helps to build the bond between a baby with his or her mother during a period when the infant has few means of communication.

"I love my dogs, and I always feel that they're more of a partner than a pet. So I started wondering, 'Why are they so close to humans? Why are they connected so tightly to us?'" Kikusui, a dog owner for the last 15 years, said.

Various breeds of dogs, including golden and Labrador retrievers, beagles and poodles were examined in the study.

This finding could help explain the process by which dogs became domesticated roughly 25,000 years ago.

Photo: Dawn Ashley | Flickr

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