Does This Explain Why Our Pets Love Us?

When you warmly gaze into the eyes of your pedigreed poodle, your rescued tabby, or even your chinchilla, you might see real love staring back at you. If you're a decent-enough pet owner, the reason seems simple: You care for your pet, and your pet cares back.

If you believe economist Paul Zak, however, you probably think your bond with Fido is only a function of brain chemistry. Zak and a team of researchers at Claremont Graduate University have studied the release of oxytocin, a hormone involved in bonding, on human social interactions. Writing in The Atlantic on Tuesday, Zak argued that oxytocin is involved in cross-species friendships as well as human ones.

If you've followed the rise of the oxytocin hype these past few years, this may not be a surprise. While oxytocin is often called "the cuddle hormone" nowadays, it was first known as the biochemical that facilitates mothering; it's produced during and after childbirth, and it triggers lactation. For decades, we've known that oxytocin plays an important role in enforcing the bond between mother and child, but it may also have a role in sexual behavior, envy, and social memory/attachment.

Zak, however, has made even loftier claims about oxytocin's powers. The author of The Moral Molecule has claimed that oxytocin can "re-bond our troubled world" and is the "source of love and prosperity."

As science writer Ed Yong has repeatedly pointed, however, oxytocin may not be so simple. "For almost a decade," Yong wrote in Slate, "this simple hormone has been relentlessly hyped as a one-ingredient recipe for a utopian society... This molecular high-five, which is released when we hug, tweet, dance, and orgasm, has been linked to trust, cooperation, empathy, and a laundry list of other virtues."

While oxytocin is certainly involved in all of those activities, that doesn't mean it only produces feelings of peace, love, and happiness; it can also trigger aggression, envy, and feelings of schadenfreude. Yong insists that trust and bonding can't simply be boiled down to a single molecule — and that Zak's tidy conclusions are just a little too "TED-dy."

But, back to Zak's latest experiments. For the first, he asked 100 human subjects to play with dogs and cats, testing their blood before and after the encounters. The verdict? Oxytocin levels went up for about 30% of participants after a puppy cuddle, but "one factor predicted whether playing with a dog would increase oxytocin: the lifetime number of pets of any type one had owned." Essentially, even longtime cat owners got an oxytocin boost after playing with a dog.

According to Zak, this experiment was inspired by the sudden feelings of sadness he experienced when a dog of his (to whom he was never particularly attached) was euthanized. "If animals caused oxytocin release in humans, it would explain my surprise attachment to my dog, Teddy, and perhaps why people spend thousands of dollars to treat a pet medically rather than euthanize it and simply get a new animal." But, does this experiment, in which only 30% of participants displayed an increase in oxytocin levels, really explain that? Couldn't Zak's grief be explained by watching an animal that has evolved to befriend humans die in front of him?

In another experiment, Zak examined the role oxytocin plays in non-human, cross-species relationships. First, he tested the blood of a dog and a goat who regularly played together at an Arkansas animal refuge. While the dog's oxytocin levels went up after playtime, as expected — suggesting to Zak that "the dog viewed the goat as a 'friend'" — the goat's went up four times more. "At that level of increase," Zak writes, "within the framework of oxytocin as the 'love hormone,' we essentially found that the goat might have been in love with the dog."

The problem with this experiment is that it equates the physiological role of a hormone in two very different mammals, and uses human metrics to explain them. Do we know that a goat's oxytocin levels are always on par with a human's? Zak also notes that the dog and goat's play involved "chasing each other, jumping towards each other, and engaging in simulated fighting (baring teeth and snarling)." Considering that oxytocin is also implicated in envy and aggression, couldn't we also deduce that the goat views the dog as a rival rather than a paramour?

Even that is too easy an explanation. Maybe the dog and goat are best friends, but increased levels of oxytocin don't necessarily prove that; the animals' interactions do. Zak's research doesn't actually explain why your pet loves you — or why you love your pet, or why animals might love each other, or even why oxytocin is released during the interactions he's studied. At the end of the day, love remains a mysterious fig. (The Atlantic)