Evolutionary Psychology and Non‑Monogamy in Humans
Human mating systems are remarkably diverse, ranging from strict monogamy to various forms of non-monogamy across different cultures and historical periods. Evolutionary psychology proposes that our species’ mating strategies are not strictly monogamous by nature, but rather reflect a mix of pair-bonding tendencies and plural mating capacities shaped by our evolutionary past. Anthropological evidence from hunter-gatherer and early agrarian societies suggests that strict lifelong monogamy was likely not the sole norm for our ancestors. Instead, humans have pursued flexible mating strategies in response to social, ecological, and reproductive pressures. This report provides a detailed, literature-based analysis of the evolutionary psychology supporting non-monogamy and open relationships in humans. It examines human mating strategies from an evolutionary perspective, reviews anthropological and historical evidence of pre-monogamous societies, discusses factors that influenced relationship formats before institutionalized monogamy, traces the rise of socially imposed monogamy, and analyzes how modern open relationships align with or deviate from evolved human behaviors.
Evolutionary Psychology Perspectives on Human Mating Strategies
Evolutionary psychologists view human mating as governed by a dual repertoire of strategies: a propensity for long-term pair-bonding alongside an opportunistic inclination toward multiple mating in the right conditions. On one hand, long-term pair bonds (enduring relationships akin to marriage) are thought to be a species-typical trait – a near-universal feature of human societies. This suggests that over evolutionary time, stable pair-bonding conferred survival advantages, likely by securing mutual parental investment in offspring. Unlike our great ape relatives (chimpanzees and bonobos), among whom long-term exclusive bonds are rare, humans evolved a psychology that readily forms strong emotional bonds between mates. These bonds are reinforced by emotions like romantic love and attachment, which help keep couples together through the demands of child-rearing.
At the same time, human mating is not limited to strict monogamy. Evolutionary theorists argue that Homo sapiens exhibit a mildly polygynous bent – meaning males in particular have evolved to seek multiple mating opportunities when possible. The evidence for this includes physical and behavioral traits: for example, humans show moderate sexual dimorphism (size differences between sexes) and intermediate testes size relative to body weight, which suggest some historical level of sperm competition and multi-partner mating (far less than highly promiscuous chimpanzees, but more than strictly monogamous gibbons). Psychological research also consistently finds that, on average, men report a desire for a larger number of sexual partners over their lifetime than women do – an asymmetry predicted by parental investment theory, since men can in principle father many offspring with multiple partners, whereas women’s reproductive output is limited by pregnancy and childbirth. Short-term mating strategies – such as casual sex or opportunistic affairs – are therefore considered part of the human repertoire, especially for males. Women, too, may pursue multiple mating under certain circumstances (e.g. to obtain better genetic quality for offspring or secure extra resources), although female short-term strategies tend to be more conditional.
Crucially, pair-bonding and multiple mating are not mutually exclusive in human evolution. A prevalent view in evolutionary psychology is that humans evolved as “serial monogamists” – forming a committed partnership for a period of time to cooperatively raise children, but potentially re-partnering or engaging in extra-pair liaisons when it was advantageous. Anthropologist Helen Fisher famously noted a cross-cultural pattern in which divorces tend to peak around the fourth year of marriage, often after a single child, suggesting an evolved cycle of serial pair-bonding rather than lifetime monogamy (sometimes dubbed the “four-year itch”). While not all scholars agree on the specific timing, the general point is that human mating bonds can be long-lasting but are not unbreakable; in ancestral environments, remating after the loss or departure of a partner (due to death, desertion, or incompatibility) would have been common, underscoring the flexibility of our mating system. Indeed, even in societies that idealize life-long marriage, a significant fraction of individuals engage in adultery or remarriage, indicating that exclusive fidelity for life is challenging for many humans, possibly because it runs counter to some evolved desires for variety or optimal mating opportunities.
Another line of evolutionary evidence comes from our emotional responses related to mating. Sexual jealousy is a near-universal human emotion, and evolutionary psychologists interpret it as an adaptive mate-guarding mechanism to defend against infidelity. Males have faced the risk of cuckoldry (raising another man’s offspring), while females have faced the risk of losing vital partner investment; jealousy evolved to deter these outcomes. The intensity of jealousy in humans – and the pain caused by a partner’s sexual or emotional infidelity – hints that non-monogamy has long been part of the human behavioral landscape, enough so that strong psychological defenses arose to police partner fidelity. In other words, if humans were naturally completely monogamous and never strayed, there would be little need for the intense jealousy we observe. The very existence of jealousy suggests that the temptation or possibility of multiple partners had to be curtailed by psychological mechanisms for pair-bonds to survive. From an evolutionary standpoint, jealousy likely functioned “to discourage infidelity” by making its costs (conflict, violence, breakups) high. This implies that while non-monogamous behavior was certainly possible (and perhaps enticing) for our ancestors, it was also risky, and those risks shaped our emotional evolution.
In sum, evolutionary psychology paints the human mating system as one of flexible monogamy or “monogamish” tendencies. Humans evolved strong pair-bonds and a taste for long-term partnership – a heritage visible in the universality of marriage and the deep attachment and cooperation seen in couples. Yet, layered atop that is a yearning for sexual diversity and additional mates under certain conditions, a legacy of our polygynous leanings. This dynamic tension can be seen as an engine that drives much of human relationship drama: a fundamental pull towards a beloved long-term partner, counterbalanced by an undercurrent of attraction to others. This evolutionary backdrop sets the stage for understanding non-monogamy in human societies, past and present: we are not “programmed” for strict monogamy so much as we are equipped with a toolkit of mating strategies that can include monogamous commitment, infidelity, and even consensual multi-partner arrangements, depending on the context.
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Anthropological Evidence from Pre-Monogamous Societies
Anthropological and cross-cultural evidence strongly supports the notion that strict monogamy has been the exception, not the rule, in human history. Surveys of the ethnographic record – notably the work of George P. Murdock and others who compiled data on hundreds of cultures – reveal that the majority of documented societies allow or accept marriage to multiple partners. In fact, approximately 85% of human societies in the anthropological record have permitted men to have more than one wife (polygyny). This means that culturally sanctioned polygynous marriage has been far more common (in terms of number of societies) than culturally enforced monogamy. Only a small fraction of societies (mostly in Western Europe and other historically Christian or modern industrial contexts) until recently insisted on exclusive monogamy as the only legal or moral form of marriage.
It is important to note, however, that permitting polygyny does not mean every man in those societies had multiple wives. Often, polygynous marriages were a privilege of high-status males or occurred in low frequencies. Among many hunter-gatherer societies – which serve as a window into early human social organization – polygyny was present but relatively moderate. For example, in foraging societies it’s been observed that on average only about 14% of married men have more than one wife, and roughly 21% of married women share a husband (have co-wives). This indicates that while the option for polygamy existed, practical constraints (such as resource availability, the need to provision each family, and sex ratios in small groups) kept monogamy as the prevailing arrangement for most individuals. In other words, “monogamish” mating – primarily monogamous with occasional polygamous unions – characterized many early societies. A similar pattern is seen in pastoral and agrarian societies: polygyny is allowed and not uncommon, but typically only a minority of men (often the wealthier or more powerful) engage in plural marriage, while the majority have only one wife.
Anthropological case studies vividly illustrate the diversity of non-monogamous arrangements in human societies prior to modern norms. In some cultures, marriage itself was not an inviolable, one-time bond but rather a fluid institution. For instance, the Mosuo people of China are famous for practicing “walking marriages,” a system with no formal marriage contracts. In this matrilineal society, women have the autonomy to invite men for overnight visits and may choose and change partners freely, with no stigma attached to ending a liaisons – a structure that strongly favors female agency in sexual relationships. Children in Mosuo communities are raised in the maternal household, and maternal relatives (mothers, uncles, grandmothers) take on the roles of caregivers, while the biological father may or may not be heavily involved. This example shows a society in which long-term pair-bonds are not institutionalized, and consensual non-monogamy is an accepted norm; multiple sequential or overlapping relationships are a normal part of life, without the expectations of exclusivity found in Western marriages.
Other indigenous societies have embraced shared or group mating practices that differ markedly from the one-man/one-woman model. In lowland South America, several tribes traditionally held the belief in “partible paternity” – the idea that a child can have more than one father. According to this belief, a fetus is formed cumulatively by the sexual contributions of multiple men; therefore, a woman who has multiple lovers during pregnancy effectively creates multiple biological fathers for her child. Anthropological research finds this belief in multiple paternity remarkably widespread in the Amazonian cultural area. In a comparative study of 128 indigenous South American societies, partible paternity was documented in a large number of them – by some estimates, such cultures are about twice as common as those with a strict belief in singular paternity. For these groups, it is socially accepted (even expected) that a pregnant woman may engage in sex with multiple men, each of whom may later act as a co-father. This practice results in the child often receiving food, care, and protection from multiple men who each consider themselves (to some degree) the father, thereby pooling paternal investment. Partible paternity effectively institutionalizes a form of non-monogamy: women have multiple concurrent sexual relationships, and fatherhood is a shared role. The existence of this system underscores how non-monogamous mating could be advantageous and normalized in certain ecological and social contexts (discussed further in the next section). It also highlights that our species is capable of viewing kinship and sexual relationships in very non-exclusive terms under the right cultural conditions.
Many other examples of non-monogamous traditions abound. Some African pastoral societies have long histories of polygynous marriages where a man might marry two or more women – often this is tied to his ability to provide cattle or other bridewealth, making polygyny a sign of wealth and status. In such communities, co-wives typically have clearly defined roles and hierarchies, and while tension can exist, these arrangements are considered normal and even desirable for economic and social reasons (e.g., more wives means more children and labor, and alliances between families). On the flip side, polyandry (one woman with multiple husbands) has been rare but not absent in human history – for example, fraternal polyandry has been practiced in parts of the Himalayas (Tibet, Nepal, portions of India) where brothers jointly marry a wife. This strategy was often linked to land conservation (keeping family land from being split among heirs) and a shortage of women, illustrating again how ecology and economy can shape marriage forms. Even in ancient Mesopotamia and other early states, while monogamous marriage was common among commoners, elite males (kings, emperors) frequently maintained harems of wives and concubines, essentially practicing polygamy at the highest social strata.
Perhaps one of the most significant pieces of evidence that humans did not evolve to be strictly monogamous is the sheer ubiquity of non-monogamous tendencies across cultures. Whether it is the tacit acceptance of extramarital affairs, the formal polygynous marriages in most traditional societies, the partible paternity concept in Amazonia, or the informal visitation unions of the Mosuo – nearly everywhere we look in the ethnographic and historical record, we find that the ideal of exclusive monogamy is frequently bent or broken. Monogamy appears to be more of a socially imposed rule in certain civilizations rather than a biological given. As anthropologists have often noted, what is considered “natural” in terms of mating can vary widely: many hunter-gatherer bands were quite egalitarian and sexually permissive, with partnerships forming and dissolving with relative ease, compared to the rigid marital contracts that came later with property and inheritance in agricultural societies. The anthropological takeaway is that human mating systems have been highly flexible, and strict monogamy (especially the lifelong, sexually exclusive kind) is not the predominant pattern if one takes a broad view of human societies. This sets the stage for why, from an evolutionary perspective, non-monogamy in various forms can be seen as within the spectrum of normal human behavior.
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Social, Ecological, and Reproductive Factors in Early Relationship Formats
To understand why non-monogamous relationships were common before monogamy became institutionalized, we must consider the social, ecological, and reproductive pressures that shaped early human mating. Our Pleistocene ancestors lived in small nomadic bands as hunter-gatherers, facing challenges very different from those in modern urban life. In those conditions, certain factors made flexible mating systems not only viable but, in many cases, advantageous.
One critical factor is the high cost of raising human offspring and the need for cooperative caregiving. Human children are exceptionally altricial – born in a helpless state and remaining dependent for far longer than the young of other primates. It has been estimated that in a foraging context it takes roughly 13 million calories to raise a single human from birth to nutritional independence. This staggering requirement means that a mother would be hard-pressed to rear a child alone; she would almost certainly need help from others to provision and protect the youngster. In contrast to other great apes (where mothers generally raise offspring solo and males provide little direct care), human evolution embraced a system of “cooperative breeding” or alloparenting – essentially, childrearing became a shared group effort. Fathers, grandparents, older siblings, and other kin often contribute food, childcare, and knowledge to the developing child. Anthropologist Sarah Hrdy and others have argued that the human species evolved an unusually cooperative strategy for raising children, summarized in the saying “it takes a village to raise a child.” This is borne out by observations of contemporary hunter-gatherers and traditional societies: alloparenting is ubiquitous – for example, older siblings, aunts/uncles, and especially grandmothers commonly help feed and care for children, and human fathers (while variable) tend to invest more in their offspring than do ape fathers. Because of this cooperative dynamic, a mother did not have to rely solely on a monogamous partner for child-rearing support. If a woman could count on help from her extended family or multiple members of a band, the absence of a devoted husband might be mitigated. This social support network means that strict monogamy (one man tethered to one woman for provisioning) was not the only path to successfully raising children – group living allowed some flexibility in family structure. For instance, a child’s biological father might die or depart, yet the child could still be raised by the mother’s relatives and other group members. Or, if a woman had multiple lovers (and thus some ambiguity about paternity), those men and their kin might all feel some obligation towards the child. Alloparenting thus diluted the necessity for exclusive pair-bonds, potentially opening the door for more open mating arrangements, so long as the community ensured the child’s welfare.
Another key factor relates to female mating strategies and the risk of infanticide. In many mammals, when a new male takes over a group, he may commit infanticide – killing infants that are not his, to bring the mother back into fertility sooner and ensure his own offspring will carry on his genes. Early human females likely faced threats of violence to themselves or their children from unrelated males. One evolved counter-strategy (seen also in some primates like langur monkeys) is for females to engage in multi-male mating, thereby confusing paternity. If multiple men in a group think they might be the father of a given child, they all have a deterrent from harming the child and may even provision the mother-child pair. Anthropological research on the partible paternity systems in the Amazon, mentioned earlier, supports this idea: women who hold this belief system explicitly mate with multiple men so that each one has a stake in the offspring’s survival. The outcome is two-fold: it reduces the risk of infanticide (no man wants to harm a child that could be his) and increases resource flow to the mother and child, as each “secondary father” might contribute food or protection. Thus, under certain ecological conditions (e.g. where male provisioning is valuable but individual males are not overwhelmingly rich in resources), a woman’s optimal strategy might be polyandrous – not in the formal sense of marrying multiple husbands, but in the sense of mating with several men serially or simultaneously to secure a coalition of investors. This is quite the opposite of what a strict monogamy norm would dictate, yet it clearly had adaptive logic in those contexts. In short, reproductive pressures on females – to keep infants safe and well-fed – could favor non-monogamy in the form of multiple partnered motherhood.
From the male perspective, there were also incentives and constraints influencing mating formats. Male reproductive success tends to increase with the number of mates, which is the classic driver of polygyny: any male who could attract additional wives would potentially have more children, spreading his genes more widely. In environments where males could accumulate the resources or status needed to support extra mates, polygyny would be favored. For example, once some humans adopted herding and farming, men who controlled more livestock or land could afford multiple wives (and those wives benefited from the wealthy husband’s support). Even in hunter-gatherer groups, a particularly skilled hunter or a headman with high status might attract more than one wife. However, ecological limitations often reined in male ambitions. In very harsh environments, having even one family to feed was challenging; taking a second wife could be impossible unless the women themselves were highly productive or the group shared food widely. Additionally, in small egalitarian bands, if one man tried to monopolize many women, it could provoke conflict or sanction from other men, limiting how far polygyny could go. Anthropologists have noted that strongly egalitarian ethos in many foragers kept marriage relatively monogamous – hoarding wives was akin to hoarding food, frowned upon in societies that valued sharing.
Interestingly, human males also sometimes found non-monogamous arrangements beneficial in cooperative ways. Ethnographic reports describe cases where men share access to wives or sexual partners as part of alliance-building. In the partible paternity societies, men will sometimes voluntarily share a sexual partner and accept joint fatherhood, thereby cementing friendships or coalitions with each other. In Tibet’s historical polyandry, brothers who might otherwise compete for wives instead cooperated by jointly marrying one woman, ensuring their inherited land stayed intact and their collective offspring (nieces/nephews) carried the family line. Such examples underscore that mating arrangements before formal monogamy were shaped by more than just raw lust – social and ecological pragmatism played a huge role. Humans are strategic creatures: if sharing partners or having multiple partners could enhance survival or social standing, those practices were likely to emerge. Conversely, if exclusive pairing was more efficient under certain conditions (e.g. when two parents needed to stay tightly bonded to get a child through a particularly vulnerable period), then monogamous tendencies would be reinforced.
In summary, prior to the advent of institutionalized monogamy, humans adapted their mating systems to local conditions. In environments where cooperation and shared responsibility thrived, mating could be relatively promiscuous or plural without jeopardizing offspring survival – indeed it could improve it. Where resources were scarce or had to be tightly managed, pair-bonds and even occasional polygyny were calibrated by what the environment could support. The evolutionary legacy from this era is a human mating psychology capable of both commitment and opportunism. We are a species in which love and loyalty co-exist with a desire for variety and strategic openness. This inherent flexibility set the stage for later cultural evolution to shape and constrain our mating behavior in different directions, including the rise of socially imposed monogamy.
Historical Evolution of Relationship Formats and the Rise of Monogamy
Through the agricultural revolution and the rise of complex societies, the spectrum of human relationship formats began to narrow under the influence of new social forces. Marriage became more than a personal relationship – it turned into a socio-economic contract, often tied to property, inheritance, alliances, and religion. These changes set the stage for the gradual ascendancy of institutionalized monogamy. Historically, as societies grew in size and stratification, leaders and lawgivers grappled with regulating marriage to serve social stability. The Near Eastern and Asian ancient civilizations generally tolerated or even encouraged polygyny (especially for the elite), but in the Western world, a notable shift occurred: Classical Greece and Rome, for example, adopted formal monogamy as the legal marital system, even for emperors (though concubinage and prostitution provided outlets for non-monogamy on the side). This Greco-Roman monogamy norm was somewhat unusual relative to most other contemporaneous cultures. With the later spread of Christianity, which strongly preached monogamous marriage and condemned adultery, monogamy as a moral and legal imperative spread across Europe. Eventually, European colonial influence and globalization in the last few centuries carried these monogamous norms to many other parts of the globe, leading to the situation depicted in the figure above – where today, the majority of nations mandate monogamous marriage by law, even if culturally plural marriages were practiced in the past.
The historical transition to predominantly monogamous institutions is fascinating because, as noted, it runs counter to what basic socioeconomic theory might predict. All else equal, greater disparities in wealth or resources should enable more polygyny, since rich men can afford multiple wives. Indeed, in many early states, as inequality grew, polygyny among the upper classes was rampant (kings and nobles accumulating wives and concubines). However, over time a different pattern emerged: norms of monogamous marriage spread even as societies became wealthier and more unequal – a puzzling outcome from a purely evolutionary standpoint. Researchers have proposed that this happened through cultural evolution: norms that were beneficial for group success tended to propagate and outcompete other norms. Monogamous marriage, despite limiting individual male reproductive potential, may have conferred huge advantages at the societal level. A compelling hypothesis by Joseph Henrich and colleagues posits that normative monogamy was favored because of its pro-social effects, which improved the cohesion and functioning of societies that adopted it. By outlawing or disfavoring polygyny, communities reduced competition among men for wives. This had several knock-on benefits: it prevented a pool of unmarried, low-status men from growing too large, which in turn reduced rates of crime and violence (since historically, societies with many young men unable to find mates tend to have more unrest). Henrich et al. argue that enforcing monogamy thus lowered the incidence of murder, assault, rape, and theft, because it curtailed the fierce mate competition that can drive male aggression. Additionally, monogamy encouraged men to invest in their existing family rather than spending energy seeking additional wives. This “redirecting” of male effort led to more parental engagement and economic productivity – men worked to support their one household, saving resources, and investing in their children’s wellbeing and education. The age gap between husbands and wives also shrank under monogamy (since powerful older men could no longer monopolize young women as second or third wives), resulting in more equal partnering and arguably better spousal relations. Societies practicing monogamy saw reduced household conflict and greater relatedness within families, which likely meant less domestic violence, less child abuse, and higher child survival. All these effects made monogamous societies more stable and cooperative. Over generations, such societies could out-compete or at least grow faster and maintain internal order better than highly polygynous societies. Through a process of cultural selection (and often direct legal imposition), monogamy thus spread and became the dominant ideal.
It’s worth noting that the rise of monogamy as an institution did not eliminate human non-monogamous behavior – it merely constrained it or channeled it in particular ways. Adultery continued to occur (often at great personal risk), extramarital sexual subcultures (like concubinage, harems where still legal, or prostitution) persisted, and in some cases quasi-polygamous arrangements (mistresses, unofficial second “wives”) were informally tolerated. Nonetheless, by the 19th and 20th centuries, the global trend was toward monogamous marriage as the only legally recognized form, with a few cultural exceptions. Even regions with polygynous traditions (for example, in Africa or the Middle East) often saw a decline in actual polygamous marriages due to modernization, economic factors, and legal pressures – monogamy became both a practical norm and a deeply ingrained ideal of romantic partnership (the vision of finding “the one” true love). The historical trajectory can thus be summarized as a shift from plural mating systems that were common in our tribal past to a near-universal enforcement of monogamy in modern nation-states. This shift was driven not by a sudden change in human nature – our underlying biology did not abruptly become monogamous – but by social evolution: new religions, laws, and economic systems made monogamy advantageous at the societal level, even if it constrains some innate desires at the individual level.
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Modern Open Relationships in Evolutionary Context
In recent decades, there has been a growing openness in some parts of the world to consensual non-monogamy (CNM) – relationship arrangements in which all partners agree that romantic or sexual involvement with multiple people is acceptable. This includes practices like open marriages (committed couples who permit outside sexual partners), polyamory (participation in multiple loving relationships with the knowledge and consent of all involved), and swinging (couples consensually swapping partners for sexual encounters). The emergence and visibility of these modern open relationship styles raise an interesting question: Are such arrangements more in line with our evolved mating psychology than the strict monogamy model? In many ways, yes – they explicitly acknowledge the non-monogamous inclinations humans can have, but they do so in a negotiated, transparent manner rather than through secret infidelity.
First, looking at prevalence: although still a minority, a significant number of people are engaging in consensual non-monogamy. Recent surveys in North America and Europe have found that roughly 3–7% of adults are currently in a CNM relationship, and up to 1 in 4 adults has engaged in some form of consensual non-monogamy at least once in their lifetime. These numbers indicate that open relationships are not just a fringe phenomenon; millions of people are exploring relationship formats beyond monogamy. Furthermore, interest in non-monogamy appears to be even higher when considering desires and fantasies – for example, one study noted that non-monogamy is among the most frequently searched or fantasized-about topics online for Americans. This latent interest suggests that the idea of having multiple partners holds natural appeal to many minds (consciously or subconsciously), consistent with the evolutionary expectation that humans are not intrinsically monogamous creatures. In evolutionary terms, the fact that so many people find monogamy challenging – evidenced by rates of cheating in monogamous relationships, or the effort required to remain exclusive – and the fact that a portion of people are inclined to consensually open up their relationships, both point toward an underlying predisposition for sexual variety.
Modern open relationships can be seen as an attempt to reconcile our innate drives with our social commitments. Rather than cheating in the shadows (which is one common outcome when monogamous ideals clash with non-monogamous desires), some couples choose to mutually agree on having other partners. From an evolutionary psychology perspective, this could be viewed as a culturally novel but evolutionarily relevant strategy: it allows individuals to potentially gain the benefits of multiple mating (sexual novelty, additional romantic bonds, diversified support) without resorting to deception or dissolution of the primary partnership. Studies on people practicing consensual non-monogamy have yielded intriguing findings. Far from the stereotype that non-monogamous relationships are less loving or secure, research shows that people in CNM relationships report overall similar levels of relationship satisfaction, trust, and psychological well-being as those in monogamous relationships. They face many of the same relational challenges (communication issues, time management, etc.) and enjoy many of the same benefits (love, companionship, stability within their core relationship). One key difference, of course, is that CNM individuals do not view sexual or emotional exclusivity as a requirement for commitment – they separate the idea of fidelity from monogamy, defining fidelity instead as being honest and loyal to agreements made with their partner. In fact, one study noted that consensually non-monogamous couples often have to develop enhanced communication and trust to navigate the complexity of multiple relationships, skills that can in some cases strengthen their bond. Importantly, in CNM any extradyadic (outside the pair) relationship is not considered infidelity so long as it adheres to the mutually agreed rules; thus, the feelings of betrayal and damage that accompany secret affairs are largely avoided.
From an evolutionary viewpoint, modern open relationships might align with ancient mating patterns in some ways – but they also face challenges because of the very mechanisms that evolved to favor monogamy. Jealousy, for instance, does not simply vanish because people consent to non-monogamy. Most individuals in open relationships still experience twinges of jealousy and insecurity, since these emotions are deeply ingrained. The difference is that they acknowledge them and have negotiated ways to handle them (such as setting boundaries, communicating feelings, or practicing compersion – joy in one’s partner’s joy with someone else). Some theorists argue that consensual non-monogamy requires overriding or retraining certain evolved predispositions (like the impulse to monopolize a mate) through rational communication and empathy. In essence, it’s a trade-off: the participants accept some emotional difficulty (managing jealousy) in exchange for the rewards of variety and additional connections. Not everyone is willing or able to make that trade, which is why CNM is likely to remain a minority preference. However, the success of many CNM relationships in sustaining love and family life suggests that human mating psychology is versatile enough to accommodate non-monogamy when the social environment permits.
It’s also crucial to note the influence of the broader social context on modern open relationships. We live in societies that, by and large, remain very mononormative – that is, they assume monogamy is the default and superior way to structure a romantic life. People who engage in polyamory or open relationships often face stigma, misunderstanding, or lack of legal recognition (for instance, one cannot marry multiple partners, and only one partner might be acknowledged in hospital visitation, insurance, etc.). Research highlights a dichotomy between these negative societal views and the actual experiences of CNM individuals. Despite prevailing stereotypes that non-monogamous relationships are less healthy or serious, studies find that internally, many CNM people have very fulfilling and stable relationships. The external pressure of stigma, however, can cause stress. For example, someone in a polyamorous family might fear job discrimination or family disapproval if their relationship status became known, leading to secrecy or stress that monogamous couples don’t have to deal with. This lack of acceptance can, ironically, bring some CNM relationships closer, as they bond over being “in it together” against societal norms; but it can also break others, if the strain is too high. From an evolutionary standpoint, one could say that our societies have shifted far faster than our underlying mating psychology. We enforce a strict monogamy model through social norms and laws (a very recentdevelopment on the timescale of human evolution), yet our minds and desires still reflect a more promiscuous ancestral reality. Modern open relationships are a manifestation of that underlying reality pushing back against the constraints – they are people consciously choosing to live in a way that might be more aligned with our primal inclinations, even if it means challenging modern conventions.
Conclusion
Both evolutionary psychology and anthropological record converge on a clear insight: human beings did not evolve in a world of strict monogamy, and thus we carry a legacy of flexible mating strategies that can include non-monogamy. Our Pleistocene ancestors likely formed pair-bonds to jointly raise offspring – a tendency we see in the love and attachment between mates today – but they also likely mated with multiple partners over their lifetimes (and sometimes concurrently), as suggested by cross-cultural patterns and our own biological signals. The rise of socially imposed monogamy is a relatively recent historical development, driven by the benefits it conferred to group stability and socio-economic organization, rather than a sudden change in human nature. Monogamy became the dominant norm because it solved certain social problems and was culturally spread and enforced, not because our inherent desires fully shifted.
In the modern era, the growing visibility of open relationships and polyamory can be viewed as a testament to our evolutionary heritage: given the opportunity, some people will opt for non-monogamous arrangements that resonate with their natural urges for diversity, novelty, and multiple social bonds. These arrangements, when entered ethically and transparently, show that non-monogamy can be compatible with love, trust, and family – in effect, they separate the idea of commitment from sexual exclusivity. At the same time, participants in such relationships must navigate challenges that are themselves products of evolution (like jealousy and possessiveness) and a society largely built around monogamous ideals. Science is only beginning to study these modern manifestations systematically, but early findings indicate that consensual non-monogamy can be a healthy and viable relationship choice, effectively rediscovering an aspect of human mating that has deep roots.
Ultimately, an evolutionary perspective does not mean that humans are “meant” to be polygamous or monogamous – rather, it reveals that we are capable of both, and our actual behavior is a negotiation between our ancient predispositions and our current environments. Non-monogamy and open relationships, when viewed through the lens of evolutionary psychology, are not deviant or newfangled inventions, but in many ways a return to form – a reminder that the story of human love and sex has always been complex and varied. By examining scientific studies, anthropological accounts, and theories of our past, we gain not only a better understanding of why non-monogamy exists, but also a more empathetic view of the diverse relationship forms humans can flourish in. In essence, human mating strategies are a continuum, and both monogamy and non-monogamy lie within our evolutionary potential. The continued study of how these dynamics play out – from prehistoric tribes to post-modern polycules – will further illuminate the profound adaptability and nuance of human relationships.
References: This analysis incorporated insights from evolutionary psychology research, cross-cultural anthropological studies, and historical records. Key sources include scholarly works on human mating systems and marriage (e.g. Henrich et al., 2012 on the cultural evolution of monogamy), ethnographic studies of hunter-gatherers and tribal societies (reporting the prevalence of polygyny and unique practices like partible paternity), and contemporary research on consensual non-monogamy (e.g. Moors et al., 2024, outlining prevalence and stigma issues). These references and others are cited in-line to support each factual claim made.
