A Natural History of Female Infidelity

"Untrue" women threaten modern notions of coupledom and propriety. But new research suggests that polyandry is far from novel or unnatural in human history, and may even suggest a path into the future.

By Wednesday Martin Ph.D., published September 4, 2018 - last reviewed on September 8, 2018

Illustration by Eddie Guy
Illustration by Eddie Guy

"So here's something kind of interesting. My wife has two husbands."

Tim is a good friend and trusted confidante whom I see whenever he is in town. He is several years older than I am, dark-haired and fit, calm and positive, generous and centered. He first caught sight of Lily at work when he was in his late twenties, he told me, when they were both in the news business. "She was so confident and so independent. I found that incredibly sexy," Tim recalled. "It took me weeks, but I finally worked up the nerve to ask her out."

They had great chemistry, and one date led to another and another. Lily was direct and honest, more than any woman he'd ever been with, but she was also a great compartmentalizer. Tim was smitten.

A few weeks before their wedding, Lily told Tim, in effect, that whatever his dreams were, he should follow them, and that he had freedom to do as he wished. "She said to me then and has always said, 'Whatever it is that is a dream for you, you will be able to pursue your dreams if you're married to me. Whether you want to be able to bike across the country, or you need to have a relationship with someone else, as long as it doesn't endanger the marriage, that's OK'." It never occurred to Tim to offer anything less, once she opened the discussion.In their marriage vows, they removed "forsake all others."

Their understanding, Tim explained, was explicit, and its bedrock was the agreement that their relationship had priority. "If she ever asked me to stop seeing someone, I would, in a second," he said. Lily never asked. Tim never asked Lily, either. Their system worked: Neither knew more than he or she wanted to, nor had less than they desired of each other or others. Several years later, they had kids and decided it made sense for Lily to stay home with them for a time. "She loved being a mommy, but she really missed having a career," Tim said. Lily, however, eventually became clinically depressed, and the couple took a step that seemed logical to them: He would stay home instead.

Like their open marriage, this new domestic arrangement worked well for them, even in an era when it was rarer than it is now. Soon after their kids started school, though, Tim noticed a change in Lily. She grew increasingly distant and preoccupied. It seemed that they were talking less. Eventually some of Lily's girlfriends came to Tim, concerned that she was very much in love with a man she was seeing. "You need to tell her she needs to end this! You need to kick her out!" one insisted. Another told Tim that she blamed him for "letting Lily have too long a leash." He told me, "I found the way they talked about it mind-boggling. Like Lily was my property and I had to control her. Like she was my horse!"

Still, Tim knew he had to speak to her. Lily admitted that, yes, she was involved with someone, that things had become serious, and that this man made her happy in ways she hadn't felt before. Did this mean there was something wrong with her, or their marriage? She didn't think so. She sobbed and apologized and said she loved both this man and Tim, in different ways. "What should I do?" she asked Tim.

Tim fought back his jealousy and panic and tried to be reasonable and considerate. "I realized,OK, this is probably one of the most important decisions I'm ever going to make. I thought, I trust her, I do. And if I try to shut this down, she'll just want to be with him more. Besides, that wasn't in our vocabulary."

To Lily's surprise, Tim told her he thought she needed to continue the relationship with her boyfriend. "You need to figure it out," he advised, "and think about what this is going to mean for you and me." They had been together for 10 years at that point. "We weren't having sex that often anymore," Tim said, "because of the kids, and I think we were in a rut in that way. She was hurting."

They decided it was okay for Lily to stay with her boyfriend, whom I'll call Rick, one or two nights per week. Over time, Tim learned that Rick was everything Tim was not—big and strapping, a physical laborer who also loved to cook. After several months, the two men met. Tim was relieved that he did not dislike Rick. Many years later, when Tim was back at work and his career was booming, Rick moved into Lily and Tim's second home, where he became caretaker, chef, and a kind of "uncle" to their kids.

Tim has long had relationships with other women but says that what has kept his marriage going is a sense that he and Lily are allies. And he says the most important thing is that in their first conversation when things got difficult, "there was no feinting, no dodging, no machismo on my part. There wasn't room for it." There had been a learning curve to their open relationship, he says, but "she's my friend, and she's a protector of me and of our marriage."

Illustration by Eddie Guy
Illustration by Eddie Guy

While Lily occasionally fools around with other men—she particularly enjoys being pursued by younger guys—she has remained committed to her marriage for more than 25 years, and to her boyfriend for a decade and a half.

Tim has never seen Lily and Rick so much as hold hands. In fact, while the two of them enjoy vacationing and going to concerts together, he has never seen any physical contact between them. "It's partially out of respect to me and our kids. My kids don't want to feel like they live or have ever lived in a commune—even though they kind of do! Whatever goes on between Rick and Lily happens off-screen. There's a hierarchy there. Our marriage is at the top. Rick seems OK with it."

Tim loves Lily as much as ever, perhaps because she presented him not only with freedom but also with an ongoing challenge: "She's the one who taught me that marriage is not being each other's property. She set that as the platform of our future together."

Their arrangement may strike others as unnatural, a departure from traditional values, or even a corruption of how things are supposed to be between men and women. But we would be wrong to think of Tim and Lily as aberrant. Their strategy is informed by and consistent with the flexible social and sexual strategies that helped Homo sapiens flourish. In the words of the late anthropologist Marjorie Shostak, who famously studied the !Kung, hunter-gatherers of the Kalahari Desert, gender inequality is an aberration in the long calendar of human history. So is dyadic monogamy for life, and many of our gendered assumptions about sex.

You're My Woman

Three linked beliefs—that a woman is a man's property, that a woman's place is in the home, and that women are more "naturally" monogamous—were planted in humanity's earliest harvests, when a woman's most personal decisions were transformed into a matter of public concern and her sexual autonomy subjected to social control and legislation.

This momentous change was put into motion 10,000 to 12,000 years ago in the Jordan Valley, where hunter-gatherers began to domesticate plants, increasingly depending on food they grew rather than food they foraged. This was a watershed moment—the rise of agriculture. The narrative goes that as humans began to focus more on crops and less on freewheeling hunting and gathering, we settled down (literally), grew up (figuratively), and created the circumstances conducive to "progress." With crops came the unprecedented luxury of food surpluses. We began to store what we could—grains—for the long term, thumbing our noses at the natural disruptions that had previously caused catastrophic shortages. We not only multiplied, as the story goes, we "civilized." We built permanent villages and established larger, denser communities.

There is no doubt that agriculture bolstered the human population, but our belief that it was the lynchpin of our "progress" is difficult to justify. Relatively new findings suggest that the shift from foraging to farming was anything but a straightforward improvement. Indeed, anthropologist Jared Diamond has called it "a catastrophe from which we have never recovered." Farmers competed for resources, including water and land, birthing the concept of property and conflict over who controlled it.

And the shift changed everything between the sexes. Multiple mating had established and continually reinforced social bonds, so there were low levels of conflict. Enhanced cooperation meant all were more likely to look after one another and their young, thus improving each individual's reproductive fitness—the odds that their offspring would go on to produce offspring. There's ample supporting evidence of this theory in historical documents about aboriginal peoples everywhere from North America to the South Pacific, as well as among present-day hunter-gatherers and foragers, many of whom raise their young cooperatively and whose mating patterns are less strictly monogamous than our own.

It runs contrary to our cherished notion that "early man" hunted, supplying meat for his female partner, who waited for him in the cave with their baby, whom they raised in a biparental, monogamous pair bond, but there is growing consensus that a very different social strategy was favored by natural selection. Cooperative breeding may explain, at least in part, why Homo sapiens flourished while earlier hominins bit the dust. Our early ancestors, like contemporary hunger-gatherers, often lived matrilocally, meaning each female stayed with her kin for life. Thus highly invested relatives and other "alloparents," or helpers, who had known her since birth, were there to look out for her interests.

Illustration by Eddie Guy
Illustration by Eddie Guy

In stark contrast, in more intensely agrarian cultures, a woman was likely to leave the support system of her family to live with an unrelated man—her husband—and his kin. Today, nearly 70 percent of agricultural and postagricultural societies are patrilocal. Under the watchful eye of these strangers, and far from the protections of home, female sexuality was reorganized, as women got a clear message: You'd better behave. It was a short leap in logic to the belief that women were the property of men and that having sex with a married woman, or a married woman having sex outside her marriage, was an act of "trespass" against her husband. Further, women began having more dependent children than their nonfarming ancestors did. The relatively more sedentary agrarian lifestyle increased their fat stores and shortened their inter-birth intervals; in other words, they could have more children more quickly. All the more reason for women to conform to new beliefs and yield to new rules about female propriety.

Agriculture played a critical role in transforming female autonomy into dependence, "gendering" us in fundamental and long-lasting ways. Consider the genre of retro grade jokes about "farmers' daughters." This stock character is sexy and dumb, but less dumb when it comes to sex; in fact, she is often promiscuous, indulging with traveling salesmen and others. Sexually bold and indiscriminate, she is in need of precisely the kind of controls that agriculture allowed men to exercise over women. Let them out of your sight, these jokes imply, and they will confound paternity faster than you can say "Elly May Clampett."

But as sociologist Rae Blumberg has pointed out, it is only for less than 3 percent of Homo sapiens history that women have been transformed from competent, relatively autonomous primary producers into secondary producers who are, in some circumstances, fundamentally dependent.

Might there be real change once plough-specific circumstances are comprehensively reversed? As we complete the transition from farming and industry to workplaces that place a premium on thought, collaboration, and innovation, and as we segue to contexts like developing apps on flexible work schedules, the future starts to look a lot like the preplough past. And we see the outlines of the possibility of a world where attempts to control women's movements, bodies, and appetites seem audacious, misguided, and futile.

Where the Past Never Passed

Couples like Tim and Lily go against the grain of modern coupling, but they are also paving a way forward. Their open relationship has kept them together over the long term, and provided practical benefits—another pair of hands to help in the home, another set of watchful eyes to keep the kids safe, another driver. Their arrangement also provides Lily variety and novelty, which experts increasingly tell us are necessary not just for a man's sexual satisfaction but for a woman's too.

Over the last several decades, primatologists have challenged the assertion that monogamy is our legacy, based on their observation of non-human primate mating strategies. They have pressured a shift of perspective about how, where, and why human females practice multiple mating. Ethnographic evidence of "nonclassical polyandry," in which women have multiple partners simultaneously or over time, with little or no social censure, has been reported in 53 societies. Anthropologist Helen Fisher has said, "There exists no culture in which adultery is unknown, no cultural device or code that extinguishes philandering." Societies have attempted to extinguish female infidelity through a range of harsh and sometimes lethal strategies, from menstrual huts to clitoridectomy to honor killings. Yet in a survey of 133 societies, primatologist Meredith Small found there was not one without female infidelity. And in at least one, women make no secret of it.

In their ancestral lands in the far north of the Kunene River region of Namibia live the Himba. They are the region's last semi nomadic people—only an estimated 30,000 to 50,000 remain. The Himba grow calabash, millet, and maize but also depend on the milk and meat of their goats, sheep, and cattle. They live in compounds of two dozen or so, but they move often, setting out whenever grazing conditions decline.

Relatively isolated, the Himba have preserved many long-standing cultural practices, even as they adapt to change by shopping at supermarkets and sending their children to school. Women generally spend their days milking and tending to goats and cattle, gardening, collecting water and firewood, cooking, and repairing and building structures. They are almost always in close contact with their babies; older toddlers and children are somewhat dependent upon one another, playing as a group, with older kids informally teaching and tending to the younger ones. In the 23 compounds that UCLA anthropologist Brooke Scelza has studied, women often remain at the main camp while men make excursions to remote cattle posts, where they may stay for weeks or even months at a time.

Long-term physical separation of spouses is a fact of Himba life. So is infidelity, which anthropologists call "extra-pair partnership," "multiple mating," or "extra-dyadic sexuality." It is not uncommon for a married Himba man to take one of his several wives with him to the cattle stations, or to have a girlfriend there. And many Himba wives take lovers while their husbands are away.

A cattle-rich Himba man can have several wives. Young men typically get married for the first time at 19 or 20. Arranged unions are common, and although a man can have several wives simultaneously, a woman can have only one husband at a time. In this way, polygyny seems asymmetrically disadvantageous for women. But things are more complicated than they appear.

Illustration by Eddie Guy
Illustration by Eddie Guy

The Himba are remarkable in their relative openness about extra-pair involvements. Spouses expect a degree of consideration from each other, to be sure, and there is a code that governs how lovers are to behave—"I don't like it when her boyfriend is here in the morning when I come back from being away," one Himba man told Scelza in so many words. But affairs are a nonsecret. More extraordinary, unlike many societies where only male infidelity is tolerated, women too are relatively open about affairs. Through the embrace of a practice that in some contexts is perilous for females, and that we in the United States have pathologized, Himba women improve their lot in ways that are scientifically verifiable.

When she arrived at her field site in 2009, Scelza began a survey of mothers: "Who's your husband? Is he your first husband? How many kids do you have?"—the basics. Early in the process, one woman informed Scelza, "This child is from my husband, and these two children are omoka." Confused, Scelza asked her translator what the word meant. He explained that it meant something like, to go to the far place to get water.

Seeing the anthropologist's confusion, the translator elaborated. "I'm going to the far place to get water" was a way of creating cover, so to speak, when heading off to a tryst. Omoka describes a child a married woman conceives during an affair, fathered by someone other than her husband. The women knew whether they were having omoka children by counting back from the day of their last period and figuring out with whom they'd had sex and when. (The Himba are a "natural fertility" population—that is, without birth control.)

Scelza had read that Himba women had lovers just as the men did. But this term was something new, and she suspected that the number of omoka kids a Himba woman had could unlock some secrets about female infidelity more generally. Unlike Western populations, where women can "conceal" sexual infidelity thanks to birth control, in a society like the Himba, there will be a much closer match between rates of infidelity and extra-pair paternity. In the industrialized West, for example, rates of extra-pair paternity hover between 1 and 10 percent, but rates of female infidelity are thought to range anywhere from 10 to 50 percent.

Scelza interviewed 110 Himba women and recorded 421 births. The women attributed each of their births to either their husbands or an extramarital affair. Scelza then classified each marriage as arranged or a love match. In the end, she determined that nearly 32 percent of the women in her sample had at least one omoka birth. Of 36 women who had an extra-pair birth, 20 had one, nine had two, and six had three or more. Only 329 of the 421 births were from the women's husbands. This was the highest reported rate of extra-pair paternity in any small-scale society in the world: nearly 18 percent.

How can the Himba's beliefs and practices be so different from ours—and what factors contribute to their radically accepting view of not only female "promiscuity" but the bearing of omoka children? A comparatively relaxed attitude about extramarital sex was obviously a contributing factor. The women asked Scelza repeatedly, "Brooke, why do you sleep alone all night in your tent?" When she replied that it was because she was married, they laughed or shrugged. "That doesn't mean you can't have a lover," they insisted. "Aren't you lonely in your tent by yourself?"

But ecological and environmental factors help create a context where the conviction that it's normal for a married woman to have sex—and a baby, or two, or three—with a man who is not her husband can take root. "The Himba have few heritable resources," Scelza says, "and fathers do not invest heavily in kids." So men are at less risk of misdirecting energy and investment to children not their own. In addition, children help out around the compound, becoming net contributors at a relatively young age compared with kids in the industrialized West, where they are costly and burdensome to parents. These differences mean paternity uncertainty costs Himba men very little. And a Himba wife's lover often drops off food for the omoka child, further lowering the "cost" to the husband. Moreover, if a married man is at a remote cattle station, the benefits of guarding his wife at home to prevent her from taking a lover become prohibitive. It's impossible to be in two places at once and unpleasant to obsess over it. It is less "expensive" to develop a tolerant attitude, and enjoy a girlfriend at the cattle station who may, after all, bear him a child of his own.

As for the Himba woman, while she moves to her husband's compound upon marriage, she maintains strong ties to her own relatives, and when married women have strong binds with and access to their own kin, they have increased sexual autonomy. And there are plenty of benefits for a Himba woman with a lover: If her husband is away and she needs to pay for supplementary food, or take a child or herself to the clinic, she has a larger circle of helpers. "Unlike the Upper East Side of Manhattan, where cheating is an incredibly risky strategy if you're married to someone with high status and high wealth," Scelza says, "for Himba women it insulates against risk."

So why doesn't every Himba woman have an omoka child? Scelza discovered something else in her data: There were no omoka children born to women in love (nonarranged) matches. Of the 79 women she interviewed who had chosen their own husbands, not a single one had an omoka child, while there were omoka children in nearly 25 percent of arranged marriages. When compelled to marry a man they have not selected, Himba women's counter strategy is to do what they are asked but also what they want: They have affairs.

Scelza's research has served up a version of a population where "affairs" benefit women. But it also throws us an unexpected and richly suggestive curveball: Himba women who exercise unconstrained choice, marrying the man they pick themselves and staying true to him, have lower reproductive success—they have fewer children who survive to adulthood. Scelzais cautious about this detail. She points out that monogamy and lower reproductive success might not be a simple equation. It could be, for example, that these women, or their partners, simply have lower fertility. But the possibility that monogamy may be straight-up disadvantageous in particular contexts is a compelling and game-changing notion. Is monogamy a privilege or a prison? Is it a choice, or does it subvert choice? The lesson of the Himba is: It depends.

If we were to trace a line from our evolutionary prehistory to the present day, we would find that circumscribing female sexual autonomy is a clear theme. But the coercion and control of female choice, including the choice to mate multiply, is not comprehensive and cannot be. Tim, Lily, and the Himba remind us that we are endlessly flexible and strategic. We will continue to move on from the plough. Our sexual and social practices will continue to evolve, and if ecological circumstances come to resemble those of the long-ago past, when women were rarely dependent, they will choose the breeding and social systems that best suit their ecologically informed needs. As we sow, so shall we reap.

Wednesday Martin, Ph.D., is the author of UNTRUE, Primates of Park Avenue, and Stepmonster.

Adapted from the book UNTRUE by Wednesday Martin. Copyright (c) 2018 by Wednesday Martin. Reprinted by permission of Little, Brown and Company, New York, NY. All rights reserved.

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