Are We Wired To Be Monogamous?

Are we meant to be with the same partner “until death do us part?”

Are humans wired to be monogamous? Do some have a higher propensity toward monogamy than others? What drives some toward infidelity? Can science tinker with our genetic makeup to make us more faithful?

The honeymoon phase of intense, romantic love lasts between 6 months and 2 years. This is the "make it or break it" point of a relationship. Interesting. After recently asking a handful of my friends how long each of their previous relationships lasted, all fell within the 6 to 24-month period.

As I point out in How Do You Know You Love Someone?, this honeymoon phase, also known as the attraction phase, is a crazy, hormone-induced, unstable, erratic, and highly addictive type of love that can “send us temporarily insane.” However, when these intense hormones fade, we are left with a mature, committed, and authentic relationship.

We go through leaps to find love, and even greater leaps to maintain that love. We change careers, move across continents, and aggressively pursue the person we think is “the one” in order to secure our own happiness. But why are we so dependent on finding that one person for our personal well-being? What happened in our evolutionary past that wired us to think, behave, desire, and strive for such intense love?

Evolutionary history of monogamy

The brain circuitry of romantic attachment between males and females could have evolved at any point in human evolution. However, it’s speculated that it began some four million years ago with our ancestors in Eastern Africa. With the development of bipedalism in humans, females began carrying their infants in their arms as opposed to on their backs. This huge leap in evolution changed everything.

Females could not carry both their infants and tools and weaponry for protection, leaving them with the inability to protect and provide for themselves and their offspring. They needed a mate. This created the necessity for pair bonding.

“Over time, natural selection favored those with the genetic propensity to form pair bonds, and the human brain chemistry for attachment evolved, essentially out of necessity," according to Dr. Helen Fisher.

What are the brain chemicals that drive us to commit?

Each stage of a relationship (lust, attraction, and attachment) is comprised of distinct hormones.

When in lust, sex hormones testosterone and estrogen fill our bodies. Moving into the attraction phase, dopamine, norepinephrine, and serotonin take over our system, creating sweaty palms, rapid heartbeats, insomnia, and loss of appetite. Attachment is the final stage when specific bonding hormones play key roles in making couples stick together for the long haul.

Two chemical hormones, in particular, have been linked to monogamous pair bonding in this attachment stage: oxytocin and vasopressin. Animal studies have opened the doors for scientists to research these chemicals more in-depth.

The prairie vole experiment

Only 3% of mammals are monogamous. Among those 3% are the prairie voles, especially known for their monogamous behavior.

In female prairie voles, oxytocin is the key ingredient for finding a lifelong partner. When mating, a flood of oxytocin is released, which then triggers the flood of dopamine, allowing feelings of reward to take over the female’s brain circuitry. This whole process allows the female to attach to her mate and desire a lifelong partnership.

If oxytocin receptors were to be blocked, however, it can cut off the pair-bonding response and eliminate the desire for monogamy completely. Similarly, when male prairie voles were given a drug that suppresses the effect of vasopressin, the bond with their partner deteriorated immediately as they lost their devotion and failed to protect their partner from new suitors.

What drives some toward infidelity?

As mentioned earlier, each stage of a relationship (lust, attraction, and attachment) is comprised of distinct hormones. These hormones have the ability to work independently from one another, causing dangerous results.

“You can feel deep attachment for a long-term spouse, while you feel romantic love for someone else, while you feel the sex drive in situations unrelated to either partner,” as Dr. Fisher explains. This independence means it is possible to love more than one person at a time, a situation that leads to jealousy, adultery, divorce, and the possibilities of promiscuity and polygamy, with the likelihood of extra children, and thus a bigger stake in the genetic future. We were not built to be happy; we were built to reproduce.

Dr. Fisher continues, “The independence of these emotional systems may have evolved among our ancestors to enable males and females to take advantage of several mating strategies simultaneously. With this brain architecture, they could form a pair bond with one partner and practice clandestine adultery too, thereby taking advantage of rare extra mating opportunities.”

Can we tinker with genetics to be more faithful?

Dr. Steven Phelps, Integrative Biology Ph.D., found great diversity in the distribution of vasopressin receptors between individual prairie voles. Phelps suggests that this variation contributes to some voles being more faithful than others.

Meanwhile, Dr. Young says that he and his colleagues have found a lot of variation in the vasopressin-receptor gene in humans. “We may be able to do things like look at their gene sequence, look at their promoter sequence, to genotype people and correlate that with their fidelity,” he contemplates.

It has already proved possible to tinker with this genetic inheritance, with startling results. Scientists can increase the expression of the relevant receptors in prairie voles, and thus strengthen the animals' ability to attach to partners. And in 1999, Dr. Young led a team that took the prairie-vole receptor gene and inserted it into an ordinary (and therefore promiscuous) mouse. The transgenic mouse thus created was much more sociable to its mate.

Sprays to increase couple bonding?

Oxytocin is even becoming a commercially-sold product. Vero Labs, for example, aims to improve relationship bonding through an oxytocin spray. They state, “Vero Labs’ line of natural oxytocin body sprays are specifically formulated to emphasize its key role in human bonding to improve confidence, enhance relationships and strengthen bonds for our users. We recommend two sprays every 2-4 hours, with enhanced effects experienced after continued use.”

According to experiments done by Beate Ditzen at the University of Zurich, this might not be such a bad idea.

In one experiment, couples each sprayed the liquid containing oxytocin up their noses (ensuring the hormone reached the brain). Each couple then talked with each other about an issue that would often lead to a disagreement. Ditzen observed how they communicated with each other during the discussion compared with couples who did not get the hormone. Ditzen found that oxytocin improved communication and lowered cortisol (a stress hormone) in both men and women.

However, in a more recent study, Ditzen took a different approach. Ditzen measured salivary alpha-amylase (sAA)—an enzyme tied specifically to social stress—and found that men and women responded differently. Women who got oxytocin showed a decrease in sAA whereas men showed an increase and reported more intense emotions. Counterintuitively, these men were also better at communication during conflict: they smiled more, had more eye contact, and were more open with their feelings.

Men have a tendency to withdraw during relationship conflict, leading to communication breakdown and relationship dissatisfaction on both sides. Ditzen thinks the higher emotional arousal that oxytocin-infused men experience may result in more engagement with their partner and thus more communication.

So, how about ditching couples therapy and inhaling oxytocin spray instead? Some may call this “paradise-engineering," essentially dedicated to abolishing the “biological substrates of human suffering.” With the onset of brain scanners becoming cheaper and drugs that can alter your state of mind (falling in love, mending a broken heart, or fixing broken relationships) this may be a real possibility in the near future.

The real question you have to ask yourself is… how far would you go to maintain your love?

This is part of a three-part series:
Part I: How Long Does It Take To Fall In Love?
Part II: How Do You Know You Love Someone?
Part III: Are We Wired To Be Monogamous?