Do You Really Know Oxytocin?
An Unlikely Love Professor
"Do You Really Know What Love Is?" That provocative question is, in fact, the title of a book I published in 2011. I married my wife — the woman I met during my exchange-student days in Canada — at twenty-two. By twenty-six, I had appointed myself a "romance expert" and started gathering students a couple of years my junior for what I grandly called "Introduction to the Science of Romance." Looking back, it is honestly hilarious. What could a kid that age possibly know about love? But the funny thing about teaching is that it forces you to learn. I devoured books on relationships, absorbed every theory I could find, and gradually built my own framework for understanding romantic love. That momentum carried me to public lectures and eventually into the university classroom. In 2005, I was fortunate enough to be hired as a professor at my alma mater, Yonsei University, where I created a course with the rather grandiose title: Do You Know What Love Is: Practical Advice for Successful Romance.1
A remarkable procession of Yonsei students enrolled over the years. Students nursing the wound of a first love gone wrong. Students too terrified to confess their feelings after a painful rejection. Students haunted by an admirer who would not stop following them. Students trapped in unwanted love triangles. The range of human experience that passed through that classroom was extraordinary. Somewhere along the way, teaching about love led me to define it: Love is giving, and giving again, and then turning back to ask whether the other person still needs something you have not yet offered. True love means giving without condition — even at a cost to yourself, even when the love you receive falls short of what you hoped for. It begins in empathy, in feeling what the other person feels, and it ends in selfless action. At that point in my life, I had no idea what oxytocin was, let alone that it was deeply connected to attachment, empathy, and altruism. Perhaps oxytocin had been woven into my story all along.
The Love Equation That Even Mice Understand
Without love, the human race would cease to exist. Love may well be the most powerful force our species has — the thing that propels us through hardships that should, by any rational calculation, be insurmountable. Across the vast sweep of human history, people have loved, married, and raised children. Even now, in an era when South Korea's total fertility rate has plummeted to a staggering 0.74 children per woman, dozens of couples still clasp hands every single day in convention-center wedding halls, pledging eternal devotion. The K-pop artist Rain captured this beautifully in his song "I Do":
As most readers will recognize, "I do" are the words spoken at the altar. When the officiant asks, "Do you promise to love each other until death do you part?" the bride and groom each answer, "I do." Two syllables — perhaps the shortest and most sacred promise in any language. Every married couple hopes their "I do" will stand as an unbreakable covenant. But what if oxytocin plays a central role in whether that promise holds?
I should ask the reader's patience for pivoting from the sanctity of wedding vows to the subject of rodents. But mice, it turns out, mirror humanity in a surprising number of ways — from their social instincts and eating habits to their mating patterns and approaches to birth and child-rearing. Small and unassuming as they are, there is a very good reason biology labs around the world have relied on them so extensively. Now, look at the two creatures pictured below: can you tell which is the prairie vole and which is the montane vole?
To the naked eye, they are virtually identical — the same rodent, twice over. But look more closely and a hint emerges. The one on the left is the prairie vole; the one on the right, the montane vole. How can you tell? In the left-hand photograph, a vole couple is tenderly nestled together with their pups. On the right, nothing of the sort. Despite looking nearly identical, these two species live radically different love lives. Prairie voles maintain strict, lifelong monogamy, and the males are deeply involved in parenting. Montane voles, by contrast, have no steady partner; they mate with as many individuals as possible. The males take on none of the child-rearing burden, and the females abandon their pups a mere ten days after birth. True to their name, prairie voles are the romantics of the rodent world.2
Love Potion: Oxytocin3
Dr. Larry Young, a professor at Emory University in Atlanta, spent more than twenty years comparing these two vole species to understand the role oxytocin plays in love, parenting, and social bonding. By mapping both species' brains, Dr. Young discovered that prairie voles carry oxytocin receptors in two critical regions — the prefrontal cortex and the nucleus accumbens. Montane voles do not. The brain areas dense with oxytocin receptors happen to be the same neighborhoods governed by dopamine, the reward circuit, and the neurobiology of addiction. Some researchers believe that sex activates the brain's reward pathway as a form of pleasure, driving the continued pursuit of sexual intimacy; they argue that oxytocin is what channels that raw drive into caring, empathetic, and tender behavior toward a partner. During mating, dopamine release in the nucleus accumbens surges by roughly fifty percent. Block dopamine in that same region with an antagonist, and the animal stops mating altogether. Dopamine exerts enormous influence over mating behavior — and oxytocin works hand in hand with it. So when researchers administered a compound that blocked both oxytocin and vasopressin receptors in the otherwise faithful prairie voles, the devoted couples simply stopped staying together.
If oxytocin truly underpinned prairie-vole monogamy, could science rewrite the montane vole's promiscuous nature? Dr. Young tested this directly. Through genetic manipulation, he induced oxytocin-receptor expression in montane voles — and the results were dramatic. The former philanderers began mating exclusively with a single partner, just like their prairie cousins. When Dr. Young then blocked dopamine activity in the brain, the montane voles reverted to their old ways, roaming and mating indiscriminately. He had demonstrated that dopamine is essential for oxytocin to do its work within the brain's reward circuitry.
Mice and humans are different, of course, and lab findings in rodents cannot be mapped directly onto people. But consider what we do know. Couples with higher oxytocin levels are more likely to remain together six months after declaring "Day One." Oxytocin surges when partners embrace, when they are physically intimate, and especially at the moment of orgasm. Among all mammals, humans are the only species that experiences nipple stimulation as a sexual stimulus, and that stimulation triggers a cascade of oxytocin release in the brain. Taken together, these facts build a compelling case: oxytocin is deeply involved in the formation of romantic bonds in our species, too.
In 1959, the American R&B group The Clovers released a song called "Love Potion Number Nine." In it, the narrator drinks a magical elixir and, unable to tell day from night, starts kissing everything in sight. Oxytocin is, in many ways, a real-life love potion. As Larry Young himself puts it: "Love is a kind of chemical reaction, and that reaction originates from a remarkable substance called oxytocin. Perhaps the Creator added oxytocin as a natural ingredient in our hormonal cocktail — to make us more loving, more caring, and more compassionate human beings."