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The Science of Sexism: Primate Behavior and the Culture of Sexual Coercion

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Warning: content may be triggering for survivors of sexual assault/abuse.

Chimp Riveter by Nathaniel Gold

"Chimp Riveter" by Nathaniel Gold

Elizabeth Wilde’s mouth was stuffed with cloth and her hands were tied behind her back. Hogs rummaged in the yard outside as her master, John Lumbrozo, forced himself on her repeatedly and threatened her with death if she resisted. When the 22-year old indentured servant girl later showed signs of being pregnant, witnesses reported that this respected doctor of Charles County, Maryland gave her a chemical “Phisick” that induced abortion. On a hot day in June, 1663 Elizabeth Wilde gave birth to “a Clod of blood,” while her rapist stood over her and performed the delivery of her dead fetus.

“With the fetus and afterbirth in the chamber pot,” wrote historian Amanda Lea Miracle in her dissertation on the incident, “the doctor threw the contents into the street. And, as neighbors pointed out to her, a further indignity was that any roaming pig could devour it.”

Lumbrozo had previously used sexual coercion against two other women, both of whom were his indentured servants. One, known only as Mrs. Hammond, he admitted to having sex with during his failed bid to challenge a lawsuit from her husband, Mr. John Hammond. The suit was filed, not for sexual assault, but because gossip over the incident was “severely hurting Hammond’s reputation so that his livelihood was in jeopardy.” In the other documented case, Lumbrozo attempted to force his servant, Margery Gold, to have sex with him because her husband owed him money. According to court testimony, Lumbrozo “took her and threw her upon the bed and would have forced her [but] she cried out and thereupon the doctor let her go.” The case was dismissed because there was no penile penetration.

Our society has made significant advances for women’s rights and sexual equality during the last century, but this case study from nearly 350 years ago would not be out of place in the headlines of today. Just this year Dominique Strauss-Kahn, Managing Director of the International Monetary Fund (an institution that claims to provide assistance for poor countries), was arrested for the alleged sexual assault on his maid, a refugee and rape survivor from African Guinea. According to statistics compiled by the US Equal Employment Opportunity Commission there were 12,772 workplace sexual harassment cases in 2010 (including all forms of sexual coercion, and representing a fraction of the number that actually occurred) and 84% of these cases were brought by women. Employers have gotten increasingly serious about cracking down on such abuses but during the last decade they were still held liable to the tune of $540 million. What is going on here? Could this kind of gender inequality be an intrinsic feature of human nature that we’re stuck with or is it simply a failure to create an environment that prevents such behaviors from reoccurring?

Primatologists and evolutionary biologists have taken this question seriously and have developed some surprising conclusions that could inform our approach to this issue. Unlike Randy Thornhill and Craig Palmer’s book A Natural History of Rape, a thesis that was criticized by scholars both in biology and gender studies, other evolutionary researchers have developed a much more balanced analysis. One example is from the recent edited volume Sexual Coercion in Primates and Humans by Martin Muller and Richard Wrangham. As they wrote in their introduction:

[M]ales in a number of primate species appear to use force, or the threat of force, to coerce unwilling females to mate with them….Although the utility of this distinction has been disputed, there is no doubt that sexual coercion is a potentially important mechanism of mating bias within the broad framework of sexual conflict theory.

There are three forms of sexual coercion that researchers have documented in both human and nonhuman primates: harassmentintimidation, and forced copulation. Harassment is the most common and results when males make repeated attempts to mate that imposes costs on females, intimidation is the use of physical violence inflicted on females who refuse to mate with a given male, and forced copulation (or “rape” in the human literature) is the least common form that involves violent restraint for immediate mating. The researchers found convincing evidence that the first two forms of sexual coercion (but not the third) increased the long-term reproductive success among males in Japanese macaques, baboons, and our closest evolutionary relatives the chimpanzees. This suggests that, at least for these three species, sexual coercion has been selected as an adaptive strategy in male sexual behavior.

But what about humans? This is a difficult question to answer since, for reasons of privacy, researchers can’t very well study human sexuality by stationing a field researcher in our bedrooms. However, reported statistics on extreme forms of intimidation can perhaps give an indication of how common sexual coercion is in modern societies. Therefore, in the same edited volume, Evolutionary Psychologist Martin Daly republished the findings that he and his late wife, Margo Wilson, reported in their 1996 paper in the journal Current Directions in Psychological Science (pdf here). To address this question they analyzed statistics for uxoricide (killings of wives) in England, Canada, and the United States between the years 1965 and 1990. Just like those researchers who studied nonhuman primates, Wilson and Daly operated under the assumption that the use of sexual coercion would be highest against those women with the highest “reproductive value.” In other words, men would be most likely to use threats or even violence against younger women who had the majority of their childbearing years ahead of them.

Uxoricide Statistics from Wilson and Daly (1996)

Figure 1. Uxoricide statistics for England, Canada, and the US (Chicago) show that the extremes of sexual coercion are highest among younger women. Reproduced from Wilson and Daly (1996).

Nonlethal sexual intimidation data from Wilson and Daly (1998)

Figure 2. Nonlethal sexual intimidation statistics in married and unmarried women. Reproduced from Wilson and Daly (1998).

As the graphs indicate, their results strongly supported this hypothesis. The highest number of uxoricides occurred in women from puberty to 24-years-old followed by those who were between 25 and 34 (see Figure 1). The lowest rate of uxoricide occurred in those women who were either approaching menopause or were already post-menopausal (50-years-old and older). The researchers also found identical trends for cases of sexual assault committed against both married and unmarried women, indicating that the murders likely had the same motivations as other cases of sexual violence (see Figure 2).

Of course, one objection to these trends could be that younger men are simply more violence prone and would therefore be more likely to assault their partners. However, what Wilson and Daly discovered was that older men who were with younger women actually had a higher rate of intimidation than did younger men. These conclusions fit right in with those of our nonhuman male counterparts showing sexual coercion as a reoccurring feature of human behavior. These findings still need to be compared with results from non-Western societies to eliminate any potential bias produced as the result of culture or environment. But the uncomfortable implication is just what feminist scholars have been arguing all along: the patriarchy is real and it will require committed focus to reduce or eradicate sexual coercion in modern societies.

However, an important thing to remember whenever reading about the implications of human evolution is that biology is not destiny. Fortunately, just as research with nonhuman primates has allowed us to better identify the problem in our own species, it can also provide us with some of the solutions. An important aspect of primate sexual coercion that shouldn’t be ignored is where it doesn’t exist and why. Bonobos are as closely related to us as chimpanzees are since we shared a common ancestor with both between four and six million years ago and the two species later diverged from each other only about a million years ago. There has never been an observed case of male sexual coercion in this species despite the fact that males are still somewhat larger than females.

A unique aspect of bonobo society is that they are a female-dominated species thanks to the network of support that exists between bonobo females. Chimpanzee females are largely isolated from one another, but bonobo females come to one another’s aid. While there may be genetic differences that account for the lack of sexual coercion in bonobos, one important factor is the different environment that promotes these cooperative networks and limits the usefulness of male coercion (see my interview with Frans de Waal for more on this topic). Male bonobos mate more frequently by gaining support from these female networks rather than using sexual coercion as can be found in chimpanzees. Males grow up with this “culture” and observe the older males in their troop emphasize grooming over aggression and then adapt their own behavior in order to maximize their reproductive success.

But bonobos aren’t the only ones. To illustrate how powerful the influence of culture can be for primate societies consider the most extreme example of a sexually coercive species: savanna baboons. Male baboons have been known to viciously maul a female that has rejected their advances and the level of male aggression is strongly correlated with their mating success. However, in a unique natural experiment Stanford primatologist Robert Sapolsky observed what developed when the largest and most aggressive males died out in a group known as Forest Troop (because they were feeding at the contaminated dump site of a Western safari lodge). In the intervening years Forest Group developed a culture in which kindness was rewarded more than aggression and adolescent males who migrated into the troop adopted this culture themselves. As Sapolsky related in his essay “A Natural History of Peace” for the journal Foreign Affairs (pdf here):

The results were that Forest Troop was left with males who were less aggressive and more social than average and the troop now had double its previous female-to-male ratio. The social consequences of these changes were dramatic. There remained a hierarchy among the Forest Troop males, but it was far looser than before: compared with other, more typical savanna baboon groups, high-ranking males rarely harassed subordinates and occasionally even relinquished contested resources to them. Aggression was less frequent, particularly against third parties. And rates of affiliative behaviors, such as males and females grooming each other or sitting together, soared. There were even instances, now and then, of adult males grooming each other – a behavior nearly as unprecedented as baboons sprouting wings. . . By the early 1990s, none of the original low aggression/high affiliation males of Forest Troop’s tuberculosis period was still alive; all of the group’s adult males had joined after the epidemic. Despite this, the troop’s unique social milieu persisted – as it does to this day, some 20 years after the selective bottleneck.

In other words, adolescent males that enter Forest Troop after having grown up elsewhere wind up adopting the unique behavioral style of the resident males. As defined by both anthropologists and animal behaviorists, “culture” consists of local behavioral variations, occurring for nongenetic and nonecological reasons, that last beyond the time of their originators. Forest Troop’s low aggression/high affiliation society constitutes nothing less than a multigenerational benign culture.

These nonhuman primate examples suggest that an increased focus on women’s rights might not only reduce the current levels of sexual coercion but could benefit society as a whole. If women have increased social power (both politically and economically) they would be better able to resist male sexual coercion due to stronger networks of social support. At the same time this increased social power would be expected to help create a change in male culture that would influence how young men interact with women when trying to gain sexual access.

While specific policies that protect women from coercion and exploitation remain important, what we’re ultimately after is social change. This is something that applies to men and women alike since many women actively participate in upholding sexual double standards. But while we work on promoting gender parity both politically and economically we should also follow the example of our baboon cousins and model the way that men interact with women. This means that more men should take issues of women’s rights seriously so that younger men who look up to them will follow in turn. By doing so perhaps we can create an environment where sexual coercion remains a thing of the past.

This was the ultimate tragedy for Elizabeth Wilde and her own case of sexual coercion. The culture of colonial Maryland held that if a woman became pregnant she must have consented to sex, even if there was overwhelming evidence that she had been raped. As a result, it was the victim who ended up going on trial to face felony charges for “illicit sex” and the murder of her child. In the end her only recourse was to marry the man who raped her, a resolution that was morally acceptable to this deeply Christian community, and which cleared her of all charges.

However, despite the limited options available, Elizabeth Wilde was not completely helpless and turns out to have had a reproductive strategy of her own. Once she realized that she’d been impregnated by her employer, Wilde confided in her fellow servant Joseph Dorrosell that she’d ingested “Ratsbeane” (or ratsbane, arsenic trioxide, a common poison at the time) in order to end the pregnancy. She was in terrible pain and feared death. It was only after Lumbrozo returned home and discovered her writhing in agony that he administered his own abortifacient. But, as Dorrosell testified, “it had done her no wrong” because it was the self-ingesting of rat poison that “did kill the child.” With little hope of finding justice in a patriarchal society, Wilde made the choice to deny her victimizer his reproductive success.

We are fortunate today, at least in the Western world, that women have expanded the choices available to them after many years of successive, slight modifications to the status quo. Evolution may provide the background for some of our species’ recurrent behavioral strategies, but we have the ability to transform our physical and cultural environments in order to influence which strategies are ultimately the most successful. Many of our primate relatives and our own species’ history offers one approach. Perhaps we can choose another.


Muller, M.N., Wrangham, R.W. (2009). Sexual Coercion in Primates and Humans: An Evolutionary Perspective on Male Aggression Against Females. Harvard University Press.

Miracle, A.L. (2008). Rape and Infanticide in Maryland, 1634-1689: Gender and Class in the Courtroom Contestation of Patriarchy on the Edge of the English Atlantic. Ph.D. Dissertation, Bowling Green State University.

Eric Michael Johnson About the Author: Eric Michael Johnson has a Master's degree in Evolutionary Anthropology focusing on great ape behavioral ecology. He is currently a doctoral student in the history of science at University of British Columbia looking at the interplay between evolutionary biology and politics.

Follow his work on Facebook and Google+. Follow on Twitter @primatediaries.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. Uncle.Al 1:31 pm 07/20/2011

    View the opening sequence of the movie “Idiocracy” (2006). Feminism is a reality deficit disorder cult of deformed decisions, an abusive hegemony of beige promulgated by feckless crapweasels.

    Women ignore rank. Women exercise seduction, juvenile behavior (including crying), then revenge. Women do not respect anything except their own transitory gains. Those who cannot compete deserve compensation. Destructive individuals are forgiven, productive individuals are flensed. A feminist society echoes with crying juveniles and stinks of filled diapers and clogged toilets.

    YOU did it! YOU weren’t happy making babies and driving black cars with stick shifts. YOU wanted pastels and automatic transmissions. YOU wanted to vote, YOU wanted to be in the workplace, YOU wanted to be in the military. YOU wanted Equal Rights, Equal Opportunity, Affirmative Action, diversity, compassion, and daycare. You’ve gotten it lady, trumped in spades redoubled. Work your butt off, abandon any thoughts of family, and watch as real experts in whining being carried in golden palanquins beat you to the finish line every time. Nobody dares hold you dearly for fear of being drawn and quartered by “social activists” and their pro bono legal representation. The best you can hope for is to get laid.

    The rub with victimology and rule of the disempowered is that there is always somebody even less qualified, a worse victim, and more screwed up than you are. You wanted a break for being a woman? Okay, but you’re a white woman and just got euchred out of that position by a Chicana two-fer. She finds herself competing against a sexually harassed intellectually challenged intravenous drug addict with AIDS Black Muslim lesbian single mother of six doing the Macarena in a wheelchair.


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  2. 2. Bora Zivkovic 2:01 pm 07/20/2011

    Next time Sapolsky finds an old aggressive baboon evicted from the troup, watching and grumbling from the outskirts as the nice, young males groom and mate and are happy, he should re-name him, aptly, Uncle Al.

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  3. 3. greg_t_laden 2:37 pm 07/20/2011

    Nobody would be mad at you if you deleted that first comment. Sort of like cleaning the bottom of your shoe off with a stick after you…

    Anyway, great post, wish I had written it myself. I may have to.

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  4. 4. comfort 2:56 pm 07/20/2011

    This is a thoughtful, careful, humane piece. I especially like the conclusion. Bravo.

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  5. 5. prass 3:22 pm 07/20/2011

    Well said UncleAl !!!
    Though such words cannot be digested by many selfish people.

    The author should be more broadminded, to learn about general behaviour of intelligent and social primates.

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  6. 6. BillNytheScienceGuy 3:57 pm 07/20/2011

    Great piece… good writing!

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  7. 7. KDCosta 4:54 pm 07/20/2011

    Eric, this is such a thoughtful, balanced discussion. Thanks for taking the time to think this through and add value to the conversations that have been happening elsewhere on the web.

    I particularly like your demonstration of cultural shifts – it is a nice illustration of the ways in which behaviors can be learned and modified over the course of a group’s existence.

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  8. 8. dudeinhammock 6:22 pm 07/20/2011

    Important post, but I wish we could declare a moratorium on using the phrase, “our closest evolutionary relative the chimpanzee.” It’s both inaccurate and misleading.

    As you mention in a later paragraph, bonobos and chimps are equally related to us. If you’ve got a brother and a sister, you don’t describe your brother as your “closest genetic relative,” do you? Then why do people who surely know much better (like you) continue to use this phrasing—especially when it obscures your central point, which is that there are two very different (but equally valid) evolutionary perspectives that can be used to gain insight into human evolution?

    I’m a big fan of your work, but that construction is way past its use-by date.

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  9. 9. Patrick Clarkin 8:28 am 07/21/2011

    Dude, you’re point is correct, but I think Johnson was referring to our “closest evolutionary relative the chimpanzees” in the plural sense of the common and pygmy variety.

    He also wrote the following:

    “bonobos are as closely related to us as chimpanzees are since we shared a common ancestor with both between four and six million years ago and the two species later diverged from each other only about a million years ago.”

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  10. 10. Uncle.Al 10:49 am 07/21/2011

    The only reality is empirical reality. The only solutions are engineering solutions. The empirical truth is that women as a group sum to dysfunction wherever they intrude into the world at large,

    (add the usual prefix through triple w, pull the spaces) / spotlight / 2011 / women /
    Kinder, Küche, Kirche, Kleider, Kannegießer… Kaput.

    The world is about building steel, creating wealth, making babies, and smashing your enemies’ faces. Female “soldiers” in Afghanistan gather into piss circles. That’s a winning tactic! Parris Island, SC is now commanded by a girl. I want to see her hair-do high and tight so the head lice don’t bite.

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  11. 11. EricMJohnson 11:41 am 07/21/2011

    I would encourage people not to respond to commenters who are being intentionally provocative. The cool grooming circle is over by the baobab tree.

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  12. 12. kclancy 11:50 am 07/21/2011

    Eric, this is great. I think you treat the topic with thoughtfulness, wit, and grace. I appreciate your perspective and conclusions, and think you do a great job encouraging us to better think on the immutability (or not) of biology. I also see a real complement to your de Waal interview, where the focus was on understanding the biology of goodness. Looking to the animals for evidence of poor behavior is not useful alone; we should seek to understand biology and culture together, and too observe and study the good with the bad.

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  13. 13. kclancy 11:51 am 07/21/2011

    Also, I’m heading to the cool grooming circle, and think Bora is hilarious. That is all.

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  14. 14. EricMJohnson 12:11 pm 07/21/2011

    I have two questions for readers, please respond or not but I’d be interested in hearing your answers. For those with some background in the life sciences, how do you see the environment and cultural behavior influencing reproductive strategies in various species? And for those who have considered issues of human gender dynamics, what does it mean to you to interrogate your privilege? What would you tell to those who have never heard of the concept? (For both questions, please avoid academic jargon. Think Carl Sagan and bell hooks.)

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  15. 15. Patrick Clarkin 1:27 pm 07/21/2011

    Regarding the question of privilege from the minds of two comedians:

    Louis CK once said that if race and gender were renewable options, he would choose white male every year.

    Chris Rock said not too many white people would trade places with him, even though he was rich.

    They’re both tongue-in-cheek comments, but good thought experiments nonetheless. We should all consider how much of our status in this world is achieved by effort and choice, and how much is ascribed and handed down to us by the social structures created by our predecessors. I don’t think any of that should be too controversial.

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  16. 16. LeeKottner 3:37 pm 07/21/2011

    Thanks for this really thoughtful piece. As a feminist, I’m usually deeply suspicious of evolutionary psychology, but you’ve taken what seems to me a very sensible and humane (no pun intended) viewpoint of it. To use evolution as an excuse for bad behavior has always seemed like the worst kind of cop-out, right next to “That woman you gave me, God, she made me do it.” Thanks for pointing out that biology isn’t destiny for anyone. If baboons can learn to change their aggressive society, surely humans can. I’ll be over at the cool grooming spot too.

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  17. 17. Carburn 5:50 pm 07/21/2011

    I see biology as simply providing us certain drives but how we go about satisfying them as culturally defined. Culture has also historically defined the role of females based on biological differences.

    I am pleased this was a very balanced article. It gives support to the idea that we can alter reproductive strategies to correspond with social changes and still be successful.

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  18. 18. JayJo 5:56 pm 07/21/2011

    What a nice piece of work! I would like to respond to your first question even in the danger of my poor English might be misleading (Sorry for that):

    To me it seems that adaptive (in terms of fitness-maximizing) reproductive strategies differ both between the sexes and also between different populations of various species since fitness pay-offs always depend on the specific opportunity cost arising within an individual’s local ecological context. Both male and female engagement in productive (e. g. growth) or reproductive (e. g. mating) tasks will have different fitness pay-offs shaped from ecological (or socioeconomic) constraints and social pressures imposed from locally present kin and non-kin (i. e. ‘culture’). E. g. among cooperative breeders, conflicting interests between the sexes should manifest into in-law conflicts between descendents of the parental lineages which might lead to the behavioral diversity apparent in different ‘kinship ecologies’.

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  19. 19. DianaLP 7:02 pm 07/21/2011

    Interrogating my privilege = shame

    Not to say that I don’t continually do it.

    This might not be exactly what you were aiming for, but what immediately comes to mind is my sexual orientation. And the double-edged sword presumed heterosexuality is. I felt attraction to girls at a very young age (before attraction to boys) and identified as bi (at least to myself and my closest siblings) at 19. So as long as my current romantic interest was male, I was afforded all the benefits of full citizenship–e.g., the right to marry and the respect (I don’t know the correct word for what I want to describe) you receive from “elders” for following the status quo–as an example, my step-father said he was proud of me the day I got married (to a man). That was the first time he’d ever said that. I was astonished. I had no idea what it was I’d done that was worthy of pride/praise.

    I predominantly dated men (in part because my hometown was small and in part because it was easy), and I married a man, so I could simply neglect to tell people I was bi and avoid all stigma. I didn’t know what that “privilege” would end up costing me, but I knew it was wrong (providing me with unearned “benefits”).

    It didn’t occur to me until after I was married to ask myself if the life I’d chosen was one that I really wanted. It happened when a professor asked the simplest question: Why marry at all? Our class was discussing “norms,” and he was making the point that people often do things without conscious thought. And he had me nabbed. I’d married my husband in large part because that was the logical next step after committing to a long-term romantic relationship. I’d never bothered to wonder whether I wanted to marry, not simply him, but anyone. And it never occurred to me that a successful relationship could end in a break up rather than marriage. Without ever really thinking about what I was doing, I was sort of sleepwalking into a very unhappy life. I dated men because people expected me to and it was easier, and I married my second boyfriend because he asked. I even fell into behaviors that had sickened me when I saw my mother doing them (working full time, going to school full time, and doing all the cooking and cleaning).

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  20. 20. EricMJohnson 2:18 pm 07/22/2011

    Thank you for those very thoughtful responses. Louis CK and Chris Rock are two of my favorite comedians for exactly that kind of biting social commentary. It’s always important to remember that scientists grow up in the same social milieu that everyone else does and internalize many of the same biases. But good science means that you carefully control the variables so as to eliminate (as much as possible) any preconceived ideas you might have.

    There are a large number of people who feel as LeeKotner does and have become very mistrustful of Evolutionary Psychologists for misinterpreting learned social behavior as aspects of our evolved nature (I will be publishing a post on this topic in the near future). Carburn and JayJo very precisely identified the problem. Male and female strategies will differ in various species but will always be altered depending on the environmental context. As the most behaviorally flexible of the primates it would be foolish to think the environment doesn’t matter where it comes to human behavior.

    But I especially want to thank DianaLP for sharing her personal story. It’s hard enough for those of us who feel well adapted to the status quo, but to live for so many years feeling like a stranger in your own body because you adopted societal expectations is something I don’t think most of us can even imagine. For me, interrogating my privilege means that I fully accept this ignorance and commit myself to being a perpetual student. It’s about listening to stories like DianaLP’s and regularly reflecting on what I take for granted that was unearned. Like Patrick Clarkin stated in another forum, “if you are born on third base, you shouldn’t delude yourself into thinking you hit a triple.”

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  21. 21. AutismDad 9:17 pm 12/2/2011

    Interesting article but one thing bothered me, the statement that DSK’s accuser was a victim of rape in her native country. The rewards for women falsely alleging rape, on every level of the legal system in the US, particularly immigration, are huge. Although she apparently got in with this claim, subsequent events have brought her honesty much into question. A scientist should not take what’s decided by a legal procedure is fact.

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