Media, Sex, Social Science

Explaining Monogamy to Vox

In the first episode of their new Netflix series, entitled Explained, the folks over at Vox set out to explain monogamy. Or at least, that is what the title (“Monogamy, Explained”) appeared to promise. But by the time it was over, very little seemed to have been explained. The central arguments, as I understand them, are that monogamy didn’t exist until after the invention of agriculture, marrying for love didn’t exist until roughly 1700 AD, and the concept of sexual selection was developed by Victorian scientists like Charles Darwin in part to justify traditional gender roles.

Vox interviews four experts for their video: relationship advice columnist Dan Savage, historian Stephanie Coontz, author Christopher Ryan, and evolutionary biologist David Barash. Of these contributors, Barash is given the least screen time. He is allowed to provide a brief description of classic sexual selection theory, noting the problem of paternity uncertainty for males, and that because of differences between sperm and eggs, males can have larger fitness payoffs by being more promiscuous than females generally can. The narrator, however, dismisses this idea, announcing that there’s a “big issue” with it (more on this later).

Ryan gets the most screen time, and the video devotes most of its time and energies to the promotion of his ideas, sometimes to comical effect. Ryan argues for the importance of sperm competition among humans—the idea that females throughout our evolutionary history were having sex with multiple males in quick succession, leading to competition between different men’s sperm to fertilize a woman’s eggs. He makes the claim that human testicle size is “intermediate” between that of gorillas, and chimpanzees and bonobos (among primates, greater sperm competition is associated with larger testicle size). As he says this, a graphic appears showing Human (34g), Gorilla (23g), Chimpanzee (149g), and Bonobo (168g) testicle size.

Vox’s image on Primate testicle size.

Saying human testicle size is “intermediate” between gorillas, and chimps and bonobos, is like saying Lebron James (2.03 m) is intermediate in height between Peter Dinklage (1.32 m) and three basketball hoops stacked on top of each other (9.15 m).

The fact that both chimps and bonobos have such large testicles means we can tentatively infer that our Last Common Ancestor before our lineage split from theirs likely had large testicles as well. If anything, this points to a significant decline in testicle size over the course of human evolutionary history, as sperm competition became less important and humans transitioned to pair-bonding.

Funnily enough, in the source from which Vox sources its testicle size data, the volume Sexual Selection and the Origins of Human Mating Systems (2009), primatologist Alan F. Dixson argues against the ideas Ryan describes regarding sperm competition in humans. Dixson writes that, “the assumption that sperm competition has played a significant role in the evolution of the genus Homo is not supported by extensive comparative studies of the reproductive anatomy and behaviour of extant primates.”

Dixson further adds that, “Human testes sizes are unexceptional and consistent with an evolutionary history which involved pair formation or polygyny as the principal mating system. Sperm competition pressure would have been low under these circumstances.”

In the video, Ryan also presents a fairly gentle picture of communal caregiving in hunter-gatherer societies, claiming that “If a child is crying, the adult nearest to that child picks it up. Nobody says, ‘Hey, Hey, your kid’s crying!’ There is a commonality to parenthood among hunter-gatherers.” The narrator then goes on to describe partible paternity (the idea that a child can have more than one father), which is found among a number of Amazonian societies.

Now, let’s compare Ryan’s claims with an excerpt from anthropologists Kim Hill and Ana Magdalena Hurtado’s work on the Ache of Paraguay. The Ache are hunter-gatherers, and also believe in partible paternity. Hill and Hurtado interview an Ache boy, who says that:

Bejaro-the-killer was really mean. Really really mean. He came back from hunting and heard my brother crying. My brother was crying a lot and wouldn’t shut up. Then Bejaro slammed him against a tree. He slammed him and he was dead. My mother was crying when my father returned from hunting. My father didn’t do anything. He was upset. He didn’t do anything. He was really afraid of Bejaro-the-killer. Bejaro was really strong. (Hill & Hurtado, 444)

Among the Ache, children whose fathers have died are also significantly more likely to be killed by adult men than children with fathers. This is precisely because people often don’t want to care for other people’s children. Further, despite what you may expect, having lots of fathers doesn’t necessarily help increase survival. As Hill and Hurtado write:

Presumably women who produced children with more than two fathers greatly reduced the confidence of paternity for all the candidate fathers and risked losing parental investment altogether. Probably for this reason children with three or more fathers appear to have fared worse than those with only one or two fathers. (Hill and Hurtado, 444)

Notice that this corroborates what David Barash had to say about the problem of paternal uncertainty, and which the Vox narrator casually dismissed.

Hill and Hurtado add that the personal stories they hear from the Ache themselves “suggest the theme of never-ending conflict between men and women over spreading of potential paternity and the production of extra children outside the marriage.” For example, an Ache child says:

My uncle was disliked [by the speaker’s father]. My dad would split his brother open and knock him down with a bow. After some point in time my father never liked his brother any more. He hated him. (My uncle) would have sex with his (my dad’s) wife. My father never liked again the one that used to have sex with his wife. He would club fight with a bow then. In the forest they would club fight with bows. (Hill and Hurtado, 443)

Another society that believes in partible paternity are the Mehinaku of Brazil. During the video, after Barash’s brief discussion of the kind of sex differences we might predict in the light of traditional sexual selection theory, the narrator criticizes his explanation, saying, “But there’s one big issue with that explanation of promiscuous, possessive men and demure women. At lots of points of time in places of the world people didn’t follow it.” As she says this, images of a number of individuals and societies are displayed and labelled for the viewer, one of which is the Mehinaku.

The main source of information on the Mehinaku is anthropologist Thomas Gregor. In Gregor’s work, we in fact see an affirmation of the “traditional story,” briefly mentioned by Barash, before being waved away by Ryan and the narrator. Gregor writes that:

“All men,” Ketepe informs me, “like sex. But women are different.” My data supports Ketepe’s belief to the extent that sexuality has a somewhat different meaning for the women than it does for the men. Men are more overtly sexual, and hence it is possible for women to use their sexuality to secure food and support in exchange for intercourse. (Gregor, 33)

Gregor expands on this, and describes how Mehinaku social norms and ideology police female sexuality:

Moreover, women are subject to repressive beliefs and practices that confine and even suffocate their sexual natures. From an early age, a girl knows that she is “just a girl” and in many respects inferior to boys. As she matures, she learns that her vagina is “smelly” and “disgusting.” She must take care that others do not see it when she sits or walks. With her first menses, she discovers that she is a danger to others. She can be held responsible for contaminating food, defiling sacred rituals, and making men sick. When she enters the network of sexual affairs, she finds that she must comport herself carefully. A casual boyfriend may seize on any unusual or uninhibited conduct in sexual relations and joke about it among his friends. One of the reasons that a woman expects gifts of her lovers is that a token of commitment is insurance that she will not be denigrated in village gossip. Even discreet sexual relationships are risky, however, since pregnancy is known to be painful and dangerous. A Mehinaku woman’s sexuality is thus linked to a sense of inferiority to men, to feelings of disgust about the genitalia, to concern about menstrual contamination, and to fear of unwanted pregnancy. (Gregor, 33)

Exactly as Barash said, and pace Ryan and the narrator, we see strong male coercion and control of female sexuality, and comparatively ‘demure’ women (though in this circumstance, we see the role of culture in enforcing this). The Mehinaku have a strongly masculine culture, with male self-worth tied characteristics such as height and body size and skills in wrestling. The Mehinaku are one of a number of strongly patriarchal societies that have ‘men’s cults.’ Women who challenge the status quo or glance at the men’s sacred instruments are threatened with gang rape. If this society is supposed to be an example of people not following ‘traditional’ gender roles, then it’s only an example insofar as they represent one of the more extreme manifestations of such behaviors.

Despite the glamorized picture of partible paternity painted by the video, as we can see with the Mehinaku, there is often still some male control over female sexuality. In a review article, anthropologist Robert S. Walker and his colleagues write that among societies with partible paternity, there is the “common theme of men allowing sexual license to wives among special male friends (e.g., Arara, Arawete, Canela, and Guaja), among real and classificatory brothers (e.g., Curripaco, Matis, Wanano, and Yanomami), and between fathers and sons (Matis).” Beliefs about partible paternity are often used by males to benefit male coalitions between friends and kin. Further, Walker et al. add that, “higher-status men…can garner female attention through better gifts, good health, and social capital. Partible paternity beliefs allow these men to father more offspring with more women and fewer repercussions (i.e., lower risk of retaliation or infanticide by jealous husbands).”

Among the Mehinaku, in Gregor’s (admittedly small) sample, the four taller, highest status males had more than double the amount of sexual partners on average than the 11 shorter, lower status males. Rather than reducing mating inequality, partible paternity tends to exacerbate it, with males having even larger variance in reproductive success in these societies, with high-status males often reaping the benefits.

There is a reason why anthropologist Joseph Henrich describes normative monogamy as “sexual egalitarianism.” It’s not that a monogamous marriage itself is unique—across the vast majority of societies, the majority of marriages have nearly always been monogamous—the key difference is primarily in the way normative monogamy acts to prevent polygyny, through social norms and legal enforcement. The main alternative to monogamy throughout history has not been an egalitarian, polyamorous free for all, but rather a relatively small number of elite males having multiple, sometimes even dozens, of wives. There are rare examples of polyandry being practiced, as I described here, but they are generally restricted to very specific socioecological conditions (such as a highly skewed sex ratio, high male mortality, extended male absence, or among brothers to maintain land inheritance) that don’t often co-occur.

In the Ethnographic Atlas, 85 percent (1041 out of 1231) of societies are coded as practicing at least occasional polygyny, with 15 percent (186 out of 1231) practicing only monogamy, and less than one percent (4 out of 1231) practicing polyandry.

Towards the end of the video, we hit aggressive levels of self-parody, when the narrator implies that the idea of sexual selection represented a Victorian-era conspiracy by patriarchal male scientists, and that monogamy is a “made up construct” and a “way to enforce gender roles”.

Yet, as Henrich and his colleagues persuasively argue, “In suppressing intrasexual competition and reducing the size of the pool of unmarried men, normative monogamy reduces crime rates, including rape, murder, assault, robbery and fraud, as well as decreasing personal abuses.” Henrich et al. sum up their argument, writing that:

We propose that the unusual package of norms and institutions that constitute modern monogamous marriage systems spread across Europe, and then the globe, because of the package’s impact on the competitive success of the polities, nations and religions that adopted this cultural package. Reducing the pool of unmarried men and levelling the reproductive playing field would have decreased crime, which would have spurred commerce, travel and the free flow of ideas and innovations.

Normative monogamy seems to have important group-level benefits, and tends to reduce the kinds of harmful behaviors associated with greater intrasexual competition, among both males and females.

Across sub-Saharan Africa, women are twice as likely to justify wife-beating as men are, and “the odds of women justifying IPVAW [intimate partner violence against women] more than men increased with increasing country polygamy rate.” If polygyny exacerbates intrasexual competition, then women may be more likely to support norms of intimate partner violence against co-wives or other women they’re competing with. And, as I noted in a previous article for Quillette, on the behavioral ecology of male violence:

There are other socioecological factors where we see an association with lethal conflict, such as the link between polygyny and war. Terrorist organizations such as Boko Haram and ISIS have exploited marriage inequality among young males by paying the brideprice (money or gifts given to a potential wife’s family), or providing wives, for recruits in the Middle East and West Africa.35 When some males monopolize access to wealth or mates, young males who are left out may behave violently to try and distinguish themselves, competing for control of such resources.

Despite the claims in the video that marrying for love is a recent phenomenon in human history, there are plenty of examples of it occurring across societies, even where marriages are usually arranged. The Kurnai of Australia had an expansive kinship system that classified many unrelated, nearby individuals as close relatives. They also had strong prohibitions against incest, and the punishment for violating them could be severe beatings or death. In such circumstances, there were numerous accounts of young women and men, who were considered ‘brother’ and ‘sister’ fleeing and eloping, while risking being killed by angry relatives. In some cases they’d spend a year ostracized, only to return a year later with a child, and grudgingly brought back into the fold. These were couples who loved each other so much, they were willing to risk being killed by their own family to be together.

Someone who fails to follow prescribed marriage rules may receive strong objections from their kin, yet you can find examples of this across numerous cultures. As anthropologist Bruce Knauft writes in his work on The Gebusi (2015) of New Guinea:

These “unreciprocated” unions provoke strong objections from the young woman’s fathers and brothers. But the young couple can prevail if the woman is strong willed or runs away with her new husband. Though the parents or brothers of the woman get upset and might beat her if they find her, many of these romantic unions endure and are ultimately accepted as marriages. (Knauft, 70)

Marrying for love isn’t new: what’s new is that people in the West today tend to have much greater freedom to do so. In his volume on The Dobe Ju/’hoansi (2013) hunter-gatherers of the Kalahari Desert, Richard Lee writes that:

All first marriages are arranged by parents, and the girls have little say in the matter. If the choice is unpopular, the girls will show their displeasure by kicking and screaming, a way of asserting their independent voice in decision making against the alliance of parents and potential husband. If they protest long and hard enough, the marriage will be called off. (Lee, 89)

Some young girls have even attempted suicide in order to get out of arranged marriages. Lee notes that close to half of all first marriages fail, and that the early periods of marriage are often turbulent. However, he also adds that:

…this level of conflict is not sustained indefinitely. After the initial stormy period Ju/′hoan couples usually settle down in a stable long-term relationship that may last 20 or 30 years or more, terminating in the death of one or another spouse. There is ample evidence that Ju men and women develop deep bonds of affection, though it is not the custom of the Ju/′hoansi to openly display it. Successful marriages are marked by joking and ease of interaction between the partners. Only about 10 percent of marriages that last five years or longer end in divorce. (Lee, 90)

We can see that the practice of arranged marriages, commonly found all over the world, primarily to form alliances or for economic reasons, often does impede a person’s ability to choose a partner for themselves. Yet even in societies with more coercive marriage practices, you find numerous examples of people rebelling against kin obligations, and prevailing norms, to marry for love.

The Himba pastoralists of Namibia have both arranged marriages chosen by kin, and ‘love matches’ determined by personal choice. While the Himba have a significant amount of ‘extra-pair births’ and high rates of adultery, there are striking differences between couples in arranged marriages compared to those in ‘love matches.’ Anthropologist Brooke A. Scelza found that, “In this sample, 31.8 percent of Himba women had at least one extra-pair (omoka) birth during their lifetime. This accounts for 17.6 percent of all marital births.” However, despite this high-rate, “Women in ‘love matches’ were significantly more faithful to their husbands than women in arranged marriages. There were no omoka children born within love matches (0 of 79), compared with 23.2 percent omoka children from arranged marriages.”

People often choose to be in monogamous pairings. Despite the perception that monogamy is coercive, overall normative monogamy constrains the behavior primarily of higher-status males, seemingly to the benefit of the rest of society.

Rather than explaining monogamy, the Vox video portrays it as something alien and largely useless. It seems like this particular narrative was deliberately chosen before a frame of video had been shot. The expert they interviewed who got much of the detail right was David Barash, yet he was given the least screen time. I suspect they chose him because he wrote a book (which the makers of the video almost certainly did not read) called The Myth of Monogamy. But once they started talking to him they were perhaps disappointed to discover that the title refers to the historical prevalence of polygyny, and not the polyamorous utopia described by Christopher Ryan.

Near the beginning of the video, soon after asserting that humans are “terrible” at monogamy, the narrator asks a central question: “Why would humans all around the world invent a rule that’s so difficult to follow, and treat breaking as such an enormous betrayal?”

I’m not sure humans are actually “terrible” at monogamy. Rather, the difficulty often lies in finding the right person, and the cultural norms and socioecological conditions that effectively promote it. Nonetheless, the question the Vox narrator asked is a fair one, which makes it all the more unfortunate that the video never attempted to answer it. We can ask this question about any number of other social norms and institutions found all over the world, such as prohibitions against theft, violence, corruption, or lying. It’s easy for many people to understand why those sorts of behaviors would be forbidden: they’re bad for society, they’re bad for the people being hurt, cheated, or deceived, they set bad examples for everyone else, etc. It’s a shame that Vox was unwilling to consider the possibility that normative monogamy fulfilled a similar function.


William Buckner is a student of Evolutionary Anthropology at UC Davis. He is interested in cultural evolution and understanding human conflict patterns across cultures. He can be followed on Twitter @Evolving_Moloch

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