There's been a lot in the news about how prevalent "hookup culture" is in college, but it turns out not all campuses are created equal when it comes to casual sex. According to a new study published by the Society for Personality and Social Psychology, one factor in particular correlates with hookups on campus: the ratio of women to men.

In one experiment, 129 straight university students read fake articles describing their local college populations as either male- or female-dominated. Then, they took a survey on how they felt about casual sex. When students read that women were the majority, more were in favor of hookups. When the articles told the opposite story, participants were more likely to advocate for committed relationships.

The authors suggest that when men are scarce, they are also highly sought after, which leads them to hold more power—at least when it comes to relationships. "If your gender is in the majority, then you have to compete with a lot of rivals, and you can't be as selective or choosy," said Justin Moss, the study's lead researcher and a psychology professor at Florida State University, in a press release. "You might also have to cater to the demands of the other sex more often."

To discover whether imbalanced ratios led to same-sex competition, the researchers had students read the same articles and then play a game allegedly against a same-sex peer (though there was actually nobody on the other end). When they won, they got to control the length and volume of a noise blasted through their opponent's headphones. Participants chose longer and louder noises when they read that their sex was in the majority, which the researcher took to indicate a sense of rivalry.

Given the correlation between gender ratios and casual sex and the growing ratio of women to men on college campuses throughout the country, it makes sense that hookup culture is on the rise. Author Jon Birger makes this argument in the book Date-onomics: How Dating Became a Lopsided Numbers Game, pointing out based on statistics and interviews with students that campus cultures often reflect gender ratios.

For example, Birger reports that at Cal Tech—where men make up 59 percent of the student body;—hookup culture is barely a thing, and men in one residence hall even wake up early on Valentine's Day to cook women pancakes and deliver handmade Valentines. On the flip side, Sarah Lawrence College, consisting of 75 percent women, has virtually no dating scene, and its students have invented the term "Golden Cock Syndrome" to describe men who milk their sought-after status.

Date-onomics also shows that imbalanced gender ratios and their resulting social dynamics last beyond college. Since there are fewer college-educated men ages 22 to 29 than women, female graduates have a smaller pool of equally-educated men to choose from. Based on Birger's interviews, straight, college-educated men often take advantage of their scarcity by playing the field and stringing women along. Annoying? Sure. On the flip side, maybe some college women prefer a more casual hook-up situation than being Facebook-official with one guy. The findings are what they are—but let's stop assuming that all women want is relationships and all men want is sex, K?

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