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“What does exclusivity mean to you?” asks Amy Hart, a contestant on UK reality TV show Love Island in 2019. Her partner, Curtis Pritchard, is cornered and she knows it. He had been kissing other girls behind her back. Pritchard shrinks into his seat as Hart eloquently and calmly lists the issues with their relationship, starting with how he could possibly have romantic feelings for two people at the same time, how she needed him, and how he had let her down.
Hart was operating under the assumption that a romantic relationship involves two people only, and that Pritchard was breaking the rules. But what we know about human relationships is that historically, they were much more complicated than the monogamy that is normal in many societies now. Might we return to our non-monogamous roots?
Consensual non-monogamy (CNM) allows both parties in a couple to be free to explore relationships with other people. This could incorporate everything from polyamory to swinging and other forms of “open” relationship. Regardless of the form it takes, one of the defining features of CNM is that partners discuss and agree the boundaries, such as for how far they can go, and when and where. This definition means that Pritchard’s antics wouldn’t come under this banner, as Hart had not signed up for them. But the presence of non-monogamy in a sizeable minority of the population might explain why Pritchard acted the way he did.
Despite the prevalence of monogamy, humans are pretty obsessed with having sex with people other than their partner. Psychologist Justin Lehmiller asked 4,000 Americans to describe their sexual fantasies for his book Tell Me What You Want. Having a threesome is the most popular fantasy, by some margin. And what is a threesome if not consensual non-monogamy?
Three isn't always a crowd - a threesome is by far the most common sexual fantasy (Credit: Getty Images)
“If we think about all the people in relationships, about 5% would define as CNM,” says Amy Muise, assistant professor of psychology at York University in Toronto, Canada. But including those who have tried CNM boosts the figure. “In lifetime experience, 21% of people have been non-monogamous at some point.”
Having a threesome is the most popular sexual fantasy, by some margin
To put that in perspective, 21% is slightly less than the number of US households who speak a language other than English at home (21.9%). “I wouldn't be surprised if it was more common,” says Amy Moors, assistant professor of psychology at Chapman University, California. “Something called social desirability explains why people give slightly conservative answers to questions. It might be why someone overestimates how often they eat five fruits or vegetables a day, or underestimates how much they drink.”
For that sizeable minority, the opportunities to meet with partners outside their household may be few right now, as measures to prevent social interactions step up in countries affected by the Covid-19 outbreak. People in CNM relationships might find themselves spending a greater amount of time with their live-in partners while having to get used to seeing their other partners a lot less. How this will affect their wellbeing is unclear, although well-established research on long-distance relationships suggests that long-distance relationships can be perfectly fulfilling. And, as social psychology tells us, in more ordinary times there are reasons to believe that people in CNM relationships may experience advantages their monogamous peers do not.
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At what point monogamy began to occur in humans is up for debate. Some anthropologists cite the fact that ancient human ancestors were strongly sexually dimorphic – that males and females were different sizes and shapes – as evidence of non-monogamy. A high degree of sexual dimorphism suggests that there are strong sexually selective pressures on one (or both) genders. In some species, like gorillas, larger males are more likely to be sexually successful by using their greater size to fight off competition from other males. A dominant male mountain gorilla will monopolise 70% of all copulations, for example, creating a polygynous society (one where many females mate with one male).
Sexual dimorphism does not always work this way. Species that use ostentatious displays of fitness, like birds with beautiful plumes and brightly coloured fish, compete for the attention of mates, rather than physically fighting off competition. The difference here is that often these are not social species, unlike humans, so one male or female would not necessarily be able to control all of their potential mates in one area.
The ancient human fossil record is patchy, though. Similar logic is also used to argue the exact opposite – that our ancient relatives had a similar level of dimorphism to us. This can be justified by looking at different fossils. Therefore monogamy might have first occurred much earlier.
The diversity, or lack-thereof, of the human Y-chromosome has also been used to suggest that humans were polygynous until relatively recently. Again, anthropologists contest the evidence, but some have suggested that the relative similarity in male genetic data suggests that only a few males were mating in our evolutionary past. More recently, this diversity has increased, which suggests that more males have been able to mate because of monogamy.
The institution of marriage only became widespread after the concept of land ownership arose, raising questions about inheritance (Credit: Getty Images)
We know from archaeological evidence that ancient humans lived in small, close extended family groups. Computer modelling of hunter-gatherer societies suggests that they needed to mate with individuals outside of their local group in order to maintain the population as a whole. There would have therefore been a large flow of mating individuals between hunter-gatherer societies. Maintaining a family whose exact genetic lineage was known would have been impossible.
This model suggests that hunter-gatherers were serially monogamous – where couples stay together exclusively for the time taken to wean a child before moving on to find a new partner. This has been shown to be sexually advantageous for modern men, which might explain why men are more interested in open relationships.
Lehmiller’s research on fantasies found that men are more interested in group sex (about 26% of men compared to 8% of women). Similar trends are also seen for other types of “social sex”, too, like interest in going to sex parties or swingers clubs (17% of men compared to 7% of women). However, those women who were interested in these fantasies were more likely to fulfil them. The number of people in the same sample who reported having taking part in group sex, for example, was 12% of men and 6% of women. It would seem, then, that women are more likely to find the right opportunities.
What we do know is that in 85% of modern human societies globally, forms of non-monogamy are sanctioned. Even the Old Testament is filled with many references to polygamy. However, the default condition in most societies is still monogamy. It might be common now, but however you look at it, historically humans were not monogamous like we are today. So why is lifetime monogamy now seen as the default?
“It is tricky to succinctly answer without saying the media,” says Moors, emphasising the impact that our art and culture play on us while growing up. “In the most part, when growing up our parents are married or trying to be monogamous. In most places worldwide we have the institution of marriage.”
“Since people started taking up land and calling it their own, that is when marriage took off because that was one clear way to keep control of your property and have it go to your family,” says Moors. “From that point we started prioritising a couple and heterosexuality.”
Is it better to see other people?
Repeatedly, research on CNM shows that couples with differing sexual interests report being better off when they have multiple sexual partners. “In a relationship often there is a discrepancy between both partners’ interests,” says Muise. “However, people with multiple partnerships might be more fulfilled overall. If you have the interest in being sexual with other people it can be healthy to explore that.”
What has been lacking in research on CNM to date has been large longitudinal studies, where groups of people who are considering opening up their relationships are followed for several years, starting even before they have that first conversation with their partner.
Some people may play different roles in a CNM relationship, with some offering nurturing care and others fulfilling erotic needs (Credit: Getty Images)
Some studies, however, are starting to fill that gap. For one, CNM-curious people and people who had never considered being open were recruited for a series of questionnaires about their relationship and sexual satisfaction. In the beginning, none of them had approached their partner to discuss the idea of opening up to other people. At the end, they were asked the same questions about how satisfied they were in their romantic lives, but also had to report whether they had opened their relationship.
“For the people who wanted to open their relationship and who did end up doing it, their satisfaction was significantly higher,” says Samantha Joel, assistant professor of social psychology at Western University in London, Canada. “Meanwhile, for the people who thought about it but didn't, their satisfaction dipped, but barely significantly.”
For the people who wanted to open their relationship and who did end up doing it, their satisfaction was significantly higher – Samantha Joel
Joel suggests that the uplift in satisfaction among people who switched to CNM might have been the result of a dragging effect. A better quality of sex life with a secondary partner drags up satisfaction with the primary partner, because suddenly the pressure of one person having to provide all of their enjoyment is removed.
“We know that when people are happier with their sex life they communicate better anyway,” says Joel. “But people in CNM report having open communication – it is difficult to be CNM if you are not talking about boundaries. Whereas in monogamous couples, those discussions about boundaries often don’t happen.”
Emotional satisfaction – feelings of security, nurturing and closeness – tends to increase in normal relationships over time. Meanwhile, spontaneity and excitement, which is linked to eroticism, decreases.
“The beginning is sexy and steamy, but then it becomes predictable,” says Rhonda Balzarini, a psychologist at York University. “Novelty is hard to maintain and there goes the steaminess.”
Balzarini gives the example of a primary partner with whom you might be legally married, live, have kids and generally have the responsibilities associated with living a monogamous life. With all the work this entails, there is more need for predictability – which is not sexy, she says. A secondary partner might never share these responsibilities with you, and so, the deterioration in the excitement of your relationship might not happen. As a result, secondary partners tend to provide a higher frequency of sex with fewer commitments.
“I think generally there is this dance between novelty and security and being in a long-term CNM relationship is a way to try to meet both needs simultaneously,” says Joel. “It’s not the only way, but it is one way and it works for some people.”
There are about as many ways to have a CNM relationship as there are people who are in them. Anita Cassidy, one of the interviewees in the video below, talks about how her and her partner manage theirs. Cassidy lives with her two children and maintains relationships with multiple partners who visit her home throughout the week. Cassidy was interviewed for this video before the Covid-19 outbreak began, and social distancing or self-isolation might limit how frequently she is able to see her partners.
How do you deal with jealousy?
The benefits of CNM are most strongly seen when primary partners are both motivated to support each other’s happiness, says Muise. “It seems like there is something about a primary wanting to see their partner sexually fulfilled but not needing to be the one who does it,” she says. “When they see their primary partner motivated by their happiness they are more comfortable getting their needs met.”
There is something about a primary wanting to see their partner sexually fulfilled but not needing to be the one who does it – Amy Muise
This describes a psychological concept called compersion – being able to experience pleasure by seeing another’s pleasure. It might be more familiar to you outside the realms of romantic relationships. Think, for example, of watching someone open a gift. But compersion has also been applied to seeing someone else sexually gratified.
So how do people in CNM couples override any feelings of jealousy? For men, jealousy is more strongly felt in relation to sexual infidelity than emotional infidelity, writes Katherine Aumer, a researcher at Hawaii Pacific University, and her co-authors in a study on compersion in both monogamous and CNM couples. We would expect this if men are more strongly motivated than women to know the paternity of their children, as evolutionary theory would suggest (Read more about what we get wrong about cheating). Identifying the maternity of their child is not hugely complicated for women.
Women are, however, more likely to feel jealous about emotional infidelity, Aumer continues. With regards to the evolutionary pressures of raising a child, women are strongly motivated to keep their male partner around so that he can provide food and protection for them and their child while they are breastfeeding. If the man appears to be emotionally invested in another woman, the mother may not be receiving the best quality food, protection and shelter from him.
Why do people choose non-monogamy?
There is evidence that certain people might be better than others at managing multiple relationships at the same time. Attachment theory describes how feelings of security or insecurity shape our relationships and might explain why some are less willing to share a partner (Read more about how attachment theory explains rebounding).
Good communication is a key component of CNM relationships, but might slip down the priority list in monogamous relationships (Credit: Getty Images)
Chris Fraley from the University of Illinois has been collecting attachment data from respondents to an online questionnaire for two decades. In total, about 200,000 people have taken this test, and many other researchers rely on this wealth of data to establish norms for all sorts of behaviours. Using this data, Moors says she has found that people engaging in poly relationships are lower on anxious attachment and avoidant attachment compared to others. However, she points out that this is a correlational finding. It could be the case that only secure, non-anxious, non-avoidant people are attracted to this lifestyle.
What the psychological profiles of CNM people might suggest is that they have emotional needs that cannot be satisfied by one person. “People in poly relationships might have higher needs in general,” says Balzarini. “We find monogamous people are on an even keel in terms of their needs for nurturance and eroticism. But poly people have high highs and low lows. They might be people who need both things simultaneously and it is hard to experience those things with only one partner. A primary partner who is nurturing is unlikely to also be exciting in an erotic way.”
We already know how to have close loving relationships with multiple people, but we are expected to believe that romantic love is limited? – Amy Moors
That said, there is very little in the way of a profile that you can build about CNM people, according to Moors. She says that there is no correlation between age, income, location, education, race, ethnicity, religion or political affiliation and CNM in her research. People who identify as lesbian, gay or bisexual are more likely to be CNM, but that is the only pattern.
For something that seems to span all walks of life, there is still a relentless stigma associated with non-monogamous lifestyles. Moors gives the example of how normal it is to think of platonic or familial love as endless, yet for some reason we consider romantic love finite. “We already know how to have close loving relationships with multiple people,” she says. “But we are expected to believe that romantic love is limited? How many best mates do you have? Oh, that’s disgusting you have one too many? That would be a ridiculous thing to say.”
We ask a lot from our partners. We expect them to be our life coach, best friend, confidant. “We don’t need all of those things from one person,” says Moors. Perhaps we would be better off by spreading our needs between more than one person.
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