When your dog gazes into your eyes, something rather wonderful may be happening inside both of you. You may be strengthening your bond through the same hormone that helps human parents form attachments to their babies.

That hormone is oxytocin, a chemical involved in affection, trust, and social bonding. Research suggests that an exchange of affectionate looks between a dog and its owner can increase oxytocin levels in both species.

In 2015, researchers at Japan's Azabu University studied 28 dogs and their owners, measuring oxytocin levels before and after they spent time together. They found that owners whose dogs gazed at them for longer periods experienced greater increases in oxytocin. Their dogs showed increases, too.

The scientists proposed that the exchange creates a positive feedback loop. A dog looks at its owner, the owner's oxytocin rises, and the resulting attention and affection may encourage more interaction, potentially reinforcing the dog's own hormonal response.

The researchers also studied a small group of wolves raised by humans from an early age. The wolves did not show the same pattern, suggesting that dogs may have developed this form of bonding during domestication. However, the wolf sample was too small to draw firm conclusions about the evolutionary difference.

Still, the findings offer an intriguing possibility. Two species with very different evolutionary histories may have learned to strengthen their attachment through a shared biological mechanism, using the same hormone involved in some of our closest human relationships.