Cuffing season, wedding season, summer flings, biological clocks, midlife affairs—pop culture and peer pressure often make us feel as though love, sex, and relationships are all supposed to happen to everyone at a prescribed time and in just the right order. And when they don't, the problem isn’t that one-size-fits-all relationship boxes are silly, it’s that you must be doing it wrong. But that's not reality. In fact, not all people are meant to be in monogamous, long-term relationships all of the time—and there’s a whole body of scientific evidence to prove that.

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Are you one of those people? Is your significant other? What do you even do with that knowledge? Here, therapist Susan Pease Gadoua, LCSW, founder of the Changing Marriage Institute and co-author of The New "I Do," and sexual relationship therapist Joe Kort, Ph.D., help us comb through the research to get to what matters.

How Our Ancestors Got Us Here

You’ve probably heard the standard evolutionary biology theory that females seek stable, long-term commitment from males because child-rearing leaves them vulnerable. Males, by contrast, seek to spread their seed far and wide. But males in some species have evolved to be monogamous nonetheless. That could be in order to prevent other males from killing their offspring, as one group of anthropologists recently posited. Another team of anthropologists looking at the same data decided that fear of infanticide isn’t the primary motivator; rather, the geographical distance between fertile females motivates mammals to stick to one partner.

Obviously, humans are driven by more than a biological imperative, and these theories don’t exactly take into account LGBTQ relationships. Evolutionary theories should really be seen as only a tiny part of the larger puzzle, given that we no longer have to worry about survival in the same way as our ancestors did—and haven't for a long time. Still, there are ways in which therapists see these concepts play out in couples regardless of gender.

Kort says that his male clients, whether in gay or straight marriages, more frequently seek to have open relationships or extramarital affairs than the women do.

"I'm inclined to think it's testosterone," Kort says, before countering his own theory by adding, "The newer thinking is, men just have more permission and women have not. Women are gaining permission, and that might change."

Gadoua also says that more of the men she works with wind up cheating than women do. And one slightly horrifying habit—which may or may not be part of an evolutionary drive—is what she's seen in new parents.

"After a baby is born, that's a high-risk time for men to be having an affair," she says. "I've seen something happen to men where they don't want to be tied down."

Motherhood has the opposite effect on some of Kort’s clients. "I frequently see this in my practice—where a couple is open, they're having kinky sex, open sex, poly sex, or whatever. Then a child is born, and the woman tends to not want to do that anymore. It's very disconcerting to the guy. It’s not at all the same in gay couples."

But perhaps payback comes later: Gadoua has seen couples in which women in their 60s wanted extramarital relationships. "When women enter menopause, their estrogen levels go down," she explains. "The estrogen is the caretaking hormone. One of my clients said, 'I'm tired of taking care of everyone else. I want my time.'"

Additionally, the idea that more men than women cheat may be changing as our culture rapidly changes. Given that more and more women work—and are achieving positions of power in their work—there's evidence to suggest that these demographics are shifting, and the cheating gender gap is closing, says Alexandra Stockwell, M.D..

"There are many reasons for this—including that co-workers get to know one another well and often spend more time together than spouses do," she says.

Genetic Hall Pass

While evolution may have passed down the notion of monogamy to some of us, that’s certainly not universal. Aside from the fact that many cultures practice polygamy, the evidence that some of us may be geared toward multiple partners is also in our genes. One study found that people with a specific type of dopamine (the pleasure-reward neurotransmitter) receptor gene reported being more sexually promiscuous and were 50 percent more likely to cheat on a spouse.

Scientists in Finland also looked at a gene that's responsible for receptors of vasopressin (a hormone associated with partner bonding, and also peeing), and observed that having lots of vasopressin receptors correlated with women's infidelity—but not men’s.

"The research is clearer and clearer that we are wired to be nonmonogamous," Kort says. "We make choices to be monogamous on purpose for children, for family, for property."

Gadoua notes that her patients’ parents have also strongly influenced their views on relationships. "Parents unconsciously say or do things that give children the idea that they don't really have to commit, or the opposite," she says. Perhaps the parents do that because they're wired to as well.

Money Matters

A recent study in Wales tested how perceptions of wealth might influence men and women to want long- or short-term relationships. After being shown photos of mansions, jewelry, fancy cars, and gold, the test subjects were asked to rate photos of models based on whether they would choose them for long-term, short-term, or no relationships—basically a lab version of "F---, Marry, Kill." Both men and women chose significantly more short-term partners than the control group that just saw photos of potted plants and groceries.

While hardly definitive, this study may indicate that notions of wealth make us more likely to consider cheating. Let's not overstate the causality here: Research doesn’t show that income leads to cheating, but this study does offer some evidence to suggest that they may be related.

"If somebody is worried about having enough food on the table and shelter and whatnot, they're going to be less likely to have unstable relationships," Gadoua reasons. "But if somebody has their basic needs met and they aren't worried about paying the bills, then they do tend to think about luxuries and having more choice in their life."

But there's also some unfortunate news in a study that shows men who aren't the primary breadwinners in hetero marriages are more likely to cheat. Gadoua has seen this happen with clients: It seems that some men still subscribe to the old definition of masculine identity, meaning being the household's main provider.

"Having an affair may be a way to get some validation that they're not getting from the workplace," she says of these men. The good news is that younger couples seem to have a better handle on this.

"Now, younger people are waiting until they've got their life pretty solid on their own and then making the decision to get married," Gadoua says. "I definitely think that if any couple can have a conversation about expectations in roles and contributions prior to getting married, they will do much better."

Thumbs Up to Polyamory and Open Marriages

Kort has observed gay male couples, in particular, having successful open relationships. A search through research databases turns up a lot of studies about men’s sexual agreements, often with regard to how this relates to their risk of contracting HIV/AIDS. (Spoiler alert: The factor here is whether they have safe sex, not necessarily their level of monogamy—of course, some monogamous couples cheat.)

Judging by the (sadly few) scientific studies about the quality of open and polyamorous relationships, the outlook is good. A survey at the University of Quebec demonstrated that there are no differences in relationship satisfaction, sexual satisfaction, trust, or commitment between people in polyamorous, open, or monogamous relationships.

In terms of biological differences, both men and women who prefer to have multiple partners have been found to have higher levels of testosterone than those who prefer having a one-and-only. However, let's remember to take this with a grain of salt—higher testosterone levels may be part of a motivation but don't lead to the behavior itself.

So How Can We Use This Science in Our Own Lives?

"It absolutely can help you have more honesty and transparency in your relationship," Gadoua says. "If you know before you go into a committed relationship that you're not good at monogamy, for example, and you say to the other person, 'This is something I know about myself, so I'm willing to be monogamous right now, but I don't know that I always will be able to,' then that person has the choice to get married or not. If you do know this about yourself and you don't share it, and then you act out later on by having multiple affairs, you've just caused a ton of wreckage."

For anyone on the other end of that conversation—if you’re someone who wants a completely monogamous commitment, this is your chance to proceed with caution or keep shopping for someone who wants the same. It doesn’t sound romantic, but open communication may be the key to happiness.

Sabrina Rojas Weiss lives in Brooklyn, surrounded by her fellow freelance writers and competitive stroller-pushers. Follow her on Twitter @shalapitcher.

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