The number of women who admit to doing the dirty (aka a sexual relationship with someone other than your spouse) has increased by 40% in the past 20 years.

But is modern life the cause or merely an opportunity? WH looks for the definitive answer to infidelity’s nature versus nurture debate.

It was the ultimate love rat – or should we say, love vole – story. The Jude Law of the animal world. Until science stepped in. One gene-altering brain injection and the Don Juan rodent fell in love.

It was 2004 and the world had just taken one giant step closer to discovering the monogamy gene, thanks to neuroscientist Dr Larry Young and his vole.

Read more: “I cheated on my husband – and this is why I did it”

Today, 92% of us want to be faithful, but only 8% of us are managing it. Men are almost twice as likely to do the dirty as women (22% compared with 12%) and one-fifth of cheaters admit that they do it regularly.

It seems that we love to love, but are drawn to cheat. And Dr Young’s voles are only part of the story…

In the decades since his groundbreaking study, the men and women in white coats have dug deeper into our DNA, discovering genes, brain wiring and hormones that encourage some of us to stray.

But there’s more to this story than a dodgy double helix. A cocktail of social changes is now interacting with physiological factors, pushing us even further away from fidelity. We’re living in the age of the perfect cheating storm.

All in the genes?

Blaming biology for a wandering eye seems like the ultimate “dog ate my homework” excuse – my genes made me do it. But they do play a part. In 2008, Swedish researcher Hasse Walum looked at how genes impact relationships. His findings were fascinating.

“He took DNA samples from 552 men and asked them detailed questions about their relationships,” explains Dr Helen Fisher, biological anthropologist and human behaviour researcher.

“Men with no copies of the specific gene – allele 334 – had very stable relationships, while men with one copy had less stable relationships and men with two copies had the least stable relationships.”

Sadly, you can’t drag your potential Mr Right down to the pharmacy for an allele 334 test, yet (although we may be able to in the future), says neuropsychiatrist Louann Brizendine, author of The Female Brain.

And there isn’t a genetic equivalent for women. “That doesn’t mean there isn’t one,” she says. “We just haven’t found it yet!”

Read more: The 5 love languages might completely transform your relationship – here’s how

But we do already know that men and women work similarly: studies of twins separated at birth have shown that if one twin is unfaithful, the other has a higher rate of infidelity – and this rule is true for both sexes.

Meanwhile, in a recent US study, a variation of the gene DRD4, called 7R+, was linked to promiscuous behaviour in both men and women.

“Not everyone with this genotype will have one-night stands or commit adultery,” explains researcher Justin Garcia. “The study merely suggests that a much higher proportion of those with this genetic type are likely to engage in these behaviours.”

No study has yet found the genetic smoking gun, the one definitive switch or trigger that makes some men Lotharios and others loyal Labradors. But together these studies show how some of us have DNA drivers that push us closer to cheating. The genes we’re born with lay the foundation for infidelity.

Humping hormones

Upon these genetic foundations sit the building blocks of modern life: those burning stars of circumstance that align to create an infidelity black hole and the other side of the cheating story.

Of course, our hectic, stressed, always-connected-but-more-alone-than-ever lives create more opportunity for us to cheat than ever before.

Our very definition of cheating has been altered – an Ashley Madison or secret Tinder profile, stealth sexting… But concurrently, these circumstances do more than just provide occasion, they’re actually rewiring our biological and neural pathways, leaving us more prone to succumbing to temptation.

Read more: This is why people start to lose interest in sex, according to science

“First, there’s oxytocin, shown to facilitate bonding between mating pairs of animals,” says neuroeconomist Paul Zak, author of The Moral Molecule: The Source of Love and Prosperity.

Oxytocin is built up by touching, hugging and kissing – a shed-load of it is pumped out after sex – and high levels are great at keeping us faithful.

“In a study of more than 1 000 men and women, it was the two percent who didn’t release enough oxytocin who had trouble in their relationships and racked up more sexual partners.”

But life today? Not so great for our O levels. First, that very modern breed of stress – the chronic, cortisol-pumping type that never gets the chance to result in either fighting or fleeing – is partly responsible for plummeting levels, zapping your stores faster than you can say, “Sex is a stress reliever, you know.”

Meanwhile, our growing fondness of personal space also plays a part. “Millions of years ago, we were surrounded by, and touched by, lots of people every day. We even slept in rows, so our levels were always topped up. Modern life is pretty lonely. Around 50% of people over 21 live alone, far from their families. They’re probably not getting the local daily touching and contact that our forebears would have,” says Zak.

Repeat stimulation

Fear not, there is good news.

The key to keeping your O levels topped up is simple: “Have regular sex,” says Zak. “The sex you had last month doesn’t help. The brain is lazy; if you’re not maintaining oxytocin levels over time, the emotional bond starts to fade because the physiological bond has gotten weaker.”

The minor hitch: apparently we’re having less sex than ever before. An in-vogue theory as to why our sex drives are shifting into neutral comes in the form of our tech obsession; that we’re too busy being aroused by the content of our apps to bother initiating nookie with whoever may be lying next to us. 

Perhaps. But there is a more certain consequence to this scenario and it relates to the neurotransmitter dopamine, the hormone that happens to create the racing-heart, still-fancy-you after- all-this-time passion that helps keep a relationship afloat.

Read more: “I had an affair with a married colleague – this is how it happened”

In Thrilled to Death: How the Endless Pursuit of Pleasure is Leaving Us Numb, Dr Archibald Hart explains that being peppered with tweets, Facebook updates and Snapchat has overloaded the pleasure centres in our brains, creating a numbness that’s driving us to seek bigger and better dopamine thrills in our lives and relationships.

We’re losing our ability to gain pleasure from normally pleasurable experiences. Just as porn has been shown to desensitise men to “real” sex, so constant overstimulation is pushing many of us to find even healthy relationships boring. We seek pleasure in riskier behaviours, including affairs.

And the constant overstimulations have turned us into a nation of impatient, sex-crazed toddlers with three-quarters of millennials agreeing that they want instant gratification (and they want it now!).

The sweet mundanity of that long-term partnership not sexy enough? Screw the long-term and get your temporary kicks from a night with someone else. Right?

Chemical reactions

Still, the story runs deeper, right down to the hormonal keystones, which make women, women and men men.

Studies, including one published in the Journal of Personality and Social Psychology, have shown that men with high testosterone levels are more likely to be unfaithful, whereas for women, oestrogen seems to be the cheating catalyst – high levels of the oestrogenic compound, oestradiol, have been linked to high rates of infidelity.

It’s a peculiarly current problem. It turns out that modern lifestyle factors are sending our oestrogen levels soaring. The adipose tissue in our expanding waistlines converts other hormones into oestrogen, the contraceptive Pill floods our systems with yet more of it, and, yes, the post-work slew of cocktails makes a difference too – even moderate alcohol intake is associated with heightened oestrogen levels.

“The oestrogen-removal process in the liver can break the oestrogen down, but if your lifestyle dictates high levels of external toxins, then your liver is put under added pressure and can often fall behind,” explains pharmacist Rita Arora.

Read more: Here’s whether you should confront the other woman about an affair

Of course, it’s not that simple. But it’s part of the bigger picture, another pulling force in the maelstrom of modern infidelity. 

The good news is that there are relatively doable strategies to cheat-proof your relationship, even if genetics and life are writing a far more complicated script for you.

“There are three things that we know from brain scans that are linked to long-term happy relationships,” says Fisher. “The first is the area for empathy, the second is the region controlling your emotions, and the third is what we call ‘positive illusions’, a brain region that enables you to overlook the negative and focus on the positive.”

Work on all three areas, she says, and you really will reduce the chances of infidelity.

And for all that the labs full of Casanova voles, cheating twins and oestrogen-sodden mice can teach us, one thing is sure – opportunity is the final piece of the puzzle.

Want to safeguard yourself from your own biology? Don’t end up drunk in a hotel room with that colleague you’ve always had a crush on. Delete that online dating profile that you’ve never bothered deactivating because, well, sometimes it’s just fun to look. 

It’s almost scientific surety that if you can, you will. Make sure you can’t.

This article was originally featured on www.womenshealthsa.co.za

Image credit: iStock

Kate Graham