Man's Best Friend

Ever wondered why humans share such a tight bond with their pet dogs? Some dog owners treat their furry friends as if they were children-- and science has a reason for this.

It turns out, dogs have inserted themselves into the hormonal loop that is responsible for scientifically solidifying the connection between a mother and its newborn child. When a mother is breastfeeding her child, her levels of oxytocin rise, causing her to feel a tighter bond to her child. Dogs are capable of triggering this same oxytocin release in their owner by a look in their eyes. And humans return the glance, inducing heightened oxytocin levels in their dog. Science writer Ed Yong aptly describes this phenomenon as a "chemical loop that unites the brains of two different species."

To test this oxytocin link between the species, scientist Miho Nagasawa allowed 30 dogs to interact with their owners. He collected urine samples from both species before and after interaction, and assessed each sample for a change in the level of oxytocin. Not only did Nagasawa find that an owner's gaze raised the dog's oxytocin levels, but he also found that the longer the owner stared at its dog, the more the dog's oxytocin levels rose. The same could be said for humans: the longer the dog stared at them, the more their oxytocin levels increased.

While humans and dogs engage in interspecies hormonal bonding, the same can't be said for wolves. Wolves maintain less eye contact with humans and the glances they do exchange do not elevate oxytocin levels. This distinction between dogs and wolves may mark the evolutionary event that caused humans to select for dog precursors in the domestication process.