When most people have questions about love or sex, they talk to friends, scour the Internet, and maybe call into a radio talk show. Me? I ask my mom, who also happens to be Sue Carter, Ph.D., the director of the Kinsey Institute and the scientist who first discovered the critical role hormones such as oxytocin play in pair-bonding (which is basically a more clinical way of saying "love"). With Valentine's Day approaching, I thought it'd be a good time to talk to Carter (writer's note: it's really weird calling your mother by her last name, but I find it unlikely that repeatedly calling a source "Mom" will be kosher with my editors) about the surprising science behind oxytocin and what we call love.
Humans aren’t the only animals that fall in love
Much of Carter’s pioneering research into oxytocin was done with prairie voles—tiny field mice that, we now know, form life-long bonds that seem conspicuously like the human notion of “love”. But in the early 1990s, it came as a huge surprise to her—and the rest of the scientific community—that a tiny rodent could experience this human-like lifelong attachment.
“I did not realize that a small mammal like a prairie vole could experience a social attachment or a bond that would last for a lifetime,” Carter says. “It just didn’t seem likely that it could be true.”
This revelation led Carter to ask the question of why—and how—these animals were sticking with their mates until death did they part. “We wanted to know: What is the glue that allows these to relationships be long-lasting,” Carter says. “In the prairie vole, we found that whatever it was, it was facilitated by sexual interactions. Which meant that whatever caused the pair bond was biological, and not just something they learned.”
That “glue” ended up being oxytocin: A formerly obscure hormone that was thought to be involved with labor and lactation, but that nobody suspected had anything to do with romantic attachment. So surprising were Carter’s findings that it took her nearly 10 years to publish them—she simply didn’t believe her own results, and assumed she must have made a mistake.
Today, we know that roughly 3-5% of mammals—not just prairie voles, but also wolves, aardvarks, marmosets and other seemingly unrelated species—experience long-lasting pair bonds. Not to mention over 90% of bird species (putting some science behind the term “love birds”). And this same chemical, oxytocin, is now known to be responsible for human bonds as well, and for much of what we call “love”.
Sue Carter, Ph.D. is the director of the Kinsey Institute (credit: Sue Carter)
Biologically speaking, sexual and romantic preferences are not the same
As a child of the 50s, Carter assumed that “monogamy” was primarily a mating system. In other words: Pair-bonded animals would prefer to be sexually exclusive and, if given the opportunity, would always select a familiar partner as a mate. In the late 1970s she discovered this was not true—and it totally took her by surprise.
Carter tells the story this way: “I was honestly disappointed. Prairie voles would pick a partner and live with that partner and have multiple babies. But when we tried to get them to exhibit a sexual preference for their familiar partner, they simply wouldn't do it. I had to face the fact that sexual preferences and social preferences were not always the same, and eventually began to call the prairie voles ‘socially monogamous.’ In retrospect and in terms of immediate survival, this makes sense: A consistent social partner matters more than who provides the sperm. Even prairie voles know and care who they live with and who helps them rear their babies.”
Oxytocin has multiple functions in the body
When Carter first began researching oxytocin, the conventional wisdom was that the molecule was only active in women, and that it was involved with little more than birth and lactation.
“Boy were we wrong,” Carter says. Recent research suggests that, in addition to being necessary for pair bonds, oxytocin helps with everything from healing burns, to strokes, high blood pressure, heart disease, kidney malfunctions, schizophrenia, and autism. In case it isn’t obvious: These are ailments that seem to have little in common with each other, making oxytocin a remarkable panacea.
Probiotics may require oxytocin to work
“Research from Susan Erdman at MIT has shown that probiotics like lactobacillus, improve skin condition, hair growth, and wound healing in a mouse model” Carter says. “But if you do the test in a genetically altered mouse that can’t make oxytocin, lactobacillus no longer has these healing properties. It will be important to know if oxytocin allows other probiotics to work.”
How we release oxytocin
We experience oxytocin in different ways: There is a pervasive always-with-us level in our systems, as well as acute pulses that come from being exposed to different scenarios—both positive and negative.
When it comes to this ambient oxytocin, individuals have different levels in their systems—levels that Carter says seem to be, at least in part, heritable. So if your parents have high levels, you may as well. This pervasive presence of oxytocin is hard at work protecting your system. For example, Carter, working with Jean-Phillipe Gouin, then at Ohio State University, found that individuals with high levels of oxytocin actually healed wounds faster and had more positive social interactions with a spouse.
Beyond the well-known triggers for acute bursts of oxytocin—going into labor and lactating, for example—there are some pretty surprising ways to release the hormone. Our bodies use oxytocin to deal with stressful situations, suggesting it may be of considerable importance in coping with life threats and danger. Although motherhood is probably the most reliable method for elevating the production of oxytocin, fathers, grandparents, and even non-relatives can also experience some of the benefits of oxytocin by simply interacting with children. A pulse of oxytocin is released following exposure to babies—and not necessarily your own baby. “In prairie voles, this effect is most easily seen in males—specifically males who haven’t had a baby before,” Carter says. It also could be useful to realize that oxytocin-releasing experiences—and you can add rollercoaster rides to that list—may offer opportunities to form new and potentially lasting relationships. After all, the hormone is as close a thing as nature has to Cupid’s arrow.
If a little oxytocin is so great, more isn't necessarily better
Before you rush to the Internet looking for oxytocin, Carter warns that artificial oxytocin, although chemically the same as the natural molecule, may have different effects depending on how it is experienced. Oxytocin is naturally delivered in pulses that are timed around specific needs and events. For example, these pulses trigger the labor contractions that allow mothers to deliver babies. “The natural way oxytocin is released is not mimicked by the medical applications,” Carter says. “At present, there are more questions than answers. We really don't know the full range of oxytocin’s effects, even under natural conditions.”
Interestingly, one of most prominent pushers of medical oxytocin is none other than pharmaceutical bad boy and Wu-Tang superfan Martin Shkreli, who sent representatives to meet with Carter and other oxytocin researchers several years ago. As it happens, Shkreli had purchased the rights to distribute an intranasal oxytocin spray.
Oxytocin literally heals a broken heart
Oxytocin is likely involved with healing heart disease, Carter says, and even plays a role in the normal development of the mammalian heart. In fact, this feat that can be recreated in a petri dish. Researchers at the University of Montreal have shown that if you take undifferentiated stem cells and put them in a dish with oxytocin, they clump together, turn into cardiomyocytes (the muscle cells that make up the heart), and begin to beat in synchrony. In other words: The molecule behind love really can heal a broken heart.
