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A Montreal male recently had the option of sleeping with a member of the opposite sex whenever he wanted.

But he also had another female in his life, one who only occasionally fulfilled his sexual desires.

Left in a room with both sexual partners, he found himself instantly drawn to the one who had been playing hard to get.

This story will not surprise most women, who have undoubtedly been told - either by peers or pop culture - not to put out too early in a relationship, lest the man lose interest.

But the fact that the Montreal love triangle took place among white lab rats may offer a new level of credence to this piece of sexual lore.

Nafissa Ismail, a graduate student at Concordia University's Centre for Studies in Behavioural Neurobiology who recorded the findings, is one of a growing number of researchers whose work attempts to explain human relationships on a biological, neurological or even genetic level.

From love at first sight to absence makes the heart grow fonder, almost every romantic cliché now has a scientific rationale.

But does this research improve the way we interact with each other, or simply encourage us to reject any relationship that doesn't follow the rules?

"I don't know if it will reinforce behaviours, but I think it should definitely give women something to think about on being too easy with men," Ms. Ismail said. "Especially if it's one that they care about and want to develop a bond with."

Her discovery that male rats show a preference for sexual prudence in their mates could be interpreted as the rodent version of The Rules, a self-help book published in 1997 that encouraged women to abide by old-fashioned mores of modesty and deference to men.

"I think what this whole study is telling us is that having easy access to sex for men does not facilitate the development of bonding with a partner," Ms. Ismail said. "The harder males have to work to get access to the female, the easier it is for them to develop a preference for that partner. And that could apply to humans too."

In recent years, scientific studies have applied their lens to other romantic notions as well, showing that opposites attract and even offering support to the idea that people should indulge in a "rebound relationship" after suffering from a broken heart.

Researchers at the University of New Mexico studied the DNA of 48 heterosexual couples, and found those with the least similar genes were the most faithful, leading one scientist to suggest future romantic partners could be tested to see if they are ideally suited for one another.

Louann Brizendine, a University of California neuropsychiatrist, suggested in her 2006 book The Female Brain that fidelity may be as innate a characteristic as blue eyes or thick hair.

In a chapter on "Love and Trust," she described scientific studies of voles that may provide a genetic explanation for monogamy. The research showed that the DNA of prairie voles, which mate in monogamous couples, contains an element missing from their furry cousins montane voles, creatures that tend to play the field. When researchers injected the missing gene into montane voles, the usually promiscuous animals instantly settled down.

Could there be a genetic basis for long-term commitment? Perhaps at least in the prairie vole, an extraordinarily faithful rodent, explains Thomas Insel, director of the Centre for Behavioural Neuroscience at Emory University school of medicine in Atlanta.

This information is no doubt fascinating to anyone who has fallen victim to a wandering eye (be it human or vole), but some say the science may discourage couples from working through a relationship problem by supporting an "it's not you, it's my genes" approach to love.

"People are always looking for reasons to explain why it didn't work," said Montreal psychotherapist and couples counsellor Vikki Stark. "Everybody wants to know this is it definitively."

"It's fun and gratifying to explain things," said Marc Abrahams, editor of the U.S. journal Annals of Improbable Research. "But the trouble is there are a lot of things that are just so complicated that it may not be possible," he said. "One of those, in my personal opinion, is this thing called love."

Benjamin Le, an assistant professor of psychology at Haverford College in Pennsylvania, says scientists cannot be unduly concerned about how people interpret their work. But he believes it could empower people to know their issues have a root in physical makeup rather than social environment.

"There's definitely neuroscience underpinnings," he said. "There's work showing when people are in love, and think about the person they love, the same areas of their brain light up as when they think about other rewarding things in their life, chocolate or whatever. . . . And anything that has a neurological basis can probably be tied into genetics."

In her Concordia research, Ms. Ismail discovered there may be a biological commonality not just in how male rats behave, but among the females as well.

When the three animals were put in an enclosure together, she said, the favoured or "prudish" female rat displayed contemptuous behaviour toward her "slutty" competitor.

"She knew that she was the familiar female. She knew that this male was her male," Ms. Ismail said. "And she engaged in a lot of mate-guarding behaviours, a way of showing that 'this is my man and I'm going to protect him.' "

It may be nice to know that even mice engage in cat fights, but scientific research of this kind does take some of the romance out of life, reducing love, jealousy and even commitment to an issue of neurological wiring.

"Everybody's aware that it can be seen that way," Mr. Abrahams acknowledges about the struggle to reconcile logic with love. "Most scientists feel, though, that learning more detail just makes it more beautiful and more mysterious."

The science of love

You tell yourself

My heart is broken.

Science tells you

Brain imaging studies have shown that romantic rejection hurts like physical pain. Helen Fisher of Rutgers University proved that the same circuits of grey matter are triggered whether you have broken up or broken a leg.

Your buddies tell you

You need a rebound.

Science tells you

It might just help. According to Louanne Brizendine, author of The Female Brain, the only surefire way out of the "brain pain" of relationship loss is to trigger a dopamine and oxytocin high - through sex.

Cat Stevens tells you

The first cut is the deepest.

Science tells you

First love really does leave an impression. A University of California, Berkeley, student found the first romantic relationship has a greater impact on an adult's love life than any other influence, including parenting.

Your mom tells you

Absence makes the heart grow fonder.

Science tells you

Human beings suffer from romantic withdrawal just like they do from drug withdrawal. Lucy Brown of the Albert Einstein College of Medicine in New York showed people pictures of their romantic partners and noticed immediate stimulation of brain areas responsible for reward and motivation.

Hollywood tells you

Opposites attract.

Science tells you

If you want to make sure he's the one, get a DNA test. Researchers at the University of New Mexico analyzed the major histocompatibility complex of 48 heterosexual couples who had been together for at least two years. The more similar a woman's MHC was to her partner's, the more likely she was to be attracted to other men.

Cosmo tells you

Girls dig the bad boy.

Science tells you

There is a reason women are drawn to emotionally unavailable men. Dr. Brizendine says females are wired to interpret an emotionless face as a signal they're doing something wrong, and to work harder to get a response.

Siri Agrell

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