When a Duke frat boy recognized a classmate in the porn clip he was watching, the gossip was just too good. He spread the news among some other bros on campus, and the rumor soon traveled from Duke's campus to the blogosphere (including Playboy SFW). Belle Knox, as the student revealed her porn identity to be, was promptly called a slut and brutally harassed online. Many people encouraged her to drop out of Duke—"a huge fucking whore" like her didn't belong among smart, educated elites.


Somehow, however, the frat boy's decision to violate Knox's privacy by outing her went mostly unquestioned. (There wasn't much coverage of him beyond this Gawker post.) The takeaway message was loud and clear: It's okay for men to enjoy porn, but the women who make it are nothing but sluts.

Unfortunately, that reaction isn't surprising. It's simply a more extreme version of a common double standard that echoes throughout the misogynistic corners of college campuses (and their corresponding blogs). "Women are sluts if they sleep around, but men are not," the bro-site Return of Kings decrees. "This fact is due to the biological differences between men and women."


Of course, the pseudo-scientific myth that all women are naturally predisposed toward sexual restraint and all men toward promiscuity isn't only inaccurate but dangerous, leading directly to the notion that women who differ from that norm are unacceptable, need to be corrected or deserve to be mistreated. What's more, it creates a culture in which men who seek out many partners aren't just celebrated, but given permission to devalue women with a similar sexual appetite.

Ironically, it's this negative attitude toward women who have casual sex that makes many women less likely to seek it out, which means less casual sex for the men who want it most. Based on what psychologists know, I'd argue that if we can work toward a culture where the stigma surrounding women's casual sex is diminished, the result could be more guilt-free hookups for all those who want them.


At first glance, some of my field's work on casual sex might appear to prove the bros right. In 1989, when undergraduates at the University of Hawaii were spontaneously asked by researchers of the opposite sex if they would join them in bed that evening, 75 percent of men—but not a single woman—agreed. Similar studies across Europe have confirmed that compared to men, women really are less likely to agree to casual sex and disapprove of it more. In fact, such a difference in desire for casual sex is one of the largest gender differences in sexuality—behind only differences in masturbation and pornography use—as two review studies from 1993 and 2010 showed.


This is where a lot of the analyses end, jumping to the conclusion that men are from Mars, women from Venus. But two important conditions make the findings less black-and-white. First, differences in the affinity for casual sex aren't absolute; they're averages. The desire for casual sex in both sexes is distributed in similar bell-shaped curves that overlap by about 50 percent. That means about one-third of women like hookups more than the average guy and about one-third of men want to hookup less than the average woman does. So even if all of the gender difference in the desire for casual sex was due to some immutable biology (as The Return of Kings and other bro sites would have you believe), a substantial minority of women would still be biologically inclined toward promiscuity and a substantial minority of men would still be biologically inclined toward monogamy.

What's more, these gender differences aren't only biological. Few scientists would deny that nature—namely, the challenges of reproduction (women's high cost of creating offspring versus men's low cost)—has played a role in gender differences toward casual sex over humankind's long evolutionary history. But nurture—namely, socializing women to be chaste and the widespread stigma against those who violate that norm—cannot be ruled out either.


Consider the results from a 2013 study of more than 24,000 students from 22 different American colleges. When asked if they'd lose respect for a man or a woman who "hooked up a lot," 28 percent of men said "yes" for a woman but "no" for a man. (Only 4 percent of women said the same thing.) Another 2013 study of almost 8,000 students at a Midwestern university arrived at a similar conclusion: Both men and women disapproved more of a woman who had casual sex (defined as sex with someone whom they've known for less than one month) than of a man.

Even more interestingly, these studies reveal that guys who seek out casual sex are the ones who are more likely to disrespect females with the same interest. For example, in one study referenced, each additional hookup reported was associated with a 4 percent increase in the odds of men holding the double standard (while the opposite was true of women). To put it another way, "sluttier" men are more likely to slut-shame women—or at least, hold negative views toward women whose promiscuity approximates their own.


This not only exposes a serious hypocrisy, but it seems counterproductive: Disrespecting women on whom your casual sex depends can only lower your chances of finding willing partners in the future, right? So why would slutty guys feel this way?

Perhaps the most obvious explanation is nurture. When misogynist environments teach men that their sexuality is fundamentally different from women (that casual sex is something for them to pursue and for women to avoid) they tend to buy in. Such views are part of a more general traditional gender ideology, explaining why studies have found that men with more traditional gender role attitudes also tend to want more casual sex. Or why in the study of students from 22 colleges mentioned above, fraternity affiliation or varsity athletic participation resulted in a 31 percent and 46 percent increase, respectively, in the odds of holding the traditional double standard. Indeed, while the desire for casual sex might be partly due to nature, genetic analyses of twins show that the tendency to support gender inequality is almost entirely due to nurture. In other words, if your environment promotes sexism, it's likely you'll hold sexist views.


That said, some men might be naturally more predisposed to end up in sexist environments. Over the years, studies consistently found that men who are more into casual sex are also more dominant, aggressive, narcissistic, arrogant, manipulative and lacking empathy. (The evidence is less clear about whether this is true for women who are more into casual sex.) Scholars have argued that these personality traits and a high interest in casual sex often cluster together as part of an exploitative short-term mating strategy where men attempt to seduce many different women—using deception (what bros would call "game") or coercion (what law enforcement would call "rape") if necessary—without feeling remorse. While such an approach might be hostile to their female partners, it allows the men to spread their seed far and wide. As such, these traits have survived (and often times, thrived) throughout our evolutionary history.

Given that these traits are largely heritable, it isn't a coincidence that many narcissistic, manipulative and coercive men find themselves in misogynistic environments: They actively seek out communities that reinforce the sexist attitudes that fit their personality. And so, a vicious cycle is created, resulting in disregard for women, particularly those they deem unworthy of respect. "It's often hard to seduce scores of women if you genuinely respect them," explains Andrew Irwin-Smiler, a psychologist whose book Challenging Casanova examines teenage masculinity and sexuality. "Respect would prevent any kind of meaningful deception—like taking advantage of drunk women. But if you think most women are 'bitches' or 'sluts,' then you can treat them like crap in order to sleep with them."


These men might also feel like the women they consider sluts not only deserve to be treated badly, but they want to be treated badly. After all, part of the repertoire of sexist attitudes is rape-myth acceptance—the belief that women "really wanted it" even when they say no, or that they "asked for it" simply by wearing provocative clothing.


Yet another explanation for the slutty-men-shaming-slutty-women phenomenon lies in the fear of unbridled female sexuality. Since an inherent part of the traditional masculinity ideology is the belief that men are the sexual initiators and predators, the existence of a highly promiscuous woman who unapologetically goes after what she wants threatens men's sense of self. As one nonsexist male blogger, My Dissolute Life, explains when writing about women who like gangbangs (perhaps the sluttiest of slutty acts), "I want, I need, to believe that I'm at the absolute center of a woman's sexual universe. ... A gangbang presents the possibility of a woman whose desire swamps that of the men, who cannot be overwhelmed by the desires of one measly guy."

And that is "more than a little terrifying." That poses a direct affront to men with fragile or "precarious masculinities," a term coined by Joseph Vandello to describe men who perceive manhood as an impermanent state that's easily lost if they fail to conform to gender norms. We know that some men respond with violence when their manhood is threatened. Slut-shaming could be just another aggressive response to this deeply felt threat to their identities.


None of this is to say that all men who are into casual sex are sexist and exploitative. (Nor that all men who aren't into casual sex are respectful and sweet.) It's certainly possible to be a highly sexual man who goes about acquiring sexual partners in an ethical way. The swinger lifestyle, for example, elaborately described in Terry Gould's The Lifestyle, is replete with examples of men who actively pursue casual sex while fully respecting the women (their own wives included) who do the same. It's just that, statistically speaking, there are more "jerks" among fans of casual sex.


Luckily, such "jerks" are a minority in the Western world. The online sexist manosphere has a vocal anti-sexist counterpart, from ManBoobz to the Good Men Project. Better yet, as sophomoric teenagers mature into young men and get exposed to the world outside of their fraternity bubbles, their double standards lessen. Even Tucker Max, the one-time king of the bros, recently gave up his "game". And since Belle Knox came out publicly about her porn career, she has been flooded with support and encouragement that has negated the insults.


More good news is that women's lesser interest in casual sex isn't immutable. For millennia, women have lived in environments that have made them dependent on men for survival and taught them to be sexually conservative. But when social and economic circumstances change to allow for greater female independence and freedom of sexual expression, gender differences in the desire for casual sex become less pronounced.

For instance, this gender difference is smaller among today's youth than it was among their parents. It's smaller in countries where political and economic power is distributed more evenly between men and women (e.g., Sweden < USA < Saudi Arabia). It's smaller when the stigma that women anticipate for accepting a casual sex offer is statistically controlled for in analyses—i.e., take that stigma away and a lot more women would consent to casual sex. And it can disappear altogether when women believe that the man offering them casual sex is a competent lover who's going to provide sexual pleasure or when that lover is famous and attractive —or famous and unattractive .


In short, put women in the right environment with the right partners, and it's likely they will desire casual sex much more than they do today, perhaps even as much as men do. Overall, the science seems to indicate that the more we talk about the tremendous individual variability in the desire for casual sex, the more the misogynistic minority will get further pushed to the fringe. Which, of course, has an added benefit: When the slut-shaming stops, everyone is likely to get laid more.

Zhana Vrangalova, PhD, is a NYC-based sex researcher who studies casual sex and nonmonogamy, teaches Human Sexuality at New York University, blogs about the science of hookups for Psychology Today, tweets daily about new sex research, and runs the Casual Sex Project, a place for people to share their true hookup stories.


Photo courtesy of MBI/Alamy