Why is Casual Sex More Common in Men than Women?

FROM THE LECTURE SERIES: Understanding the Mysteries of Human Behavior

By Mark Leary, Ph.D., Duke University

It is a common belief that men are more into casual sex than women. This time, unlike many other beliefs, science also supports the common belief. One study showed that 70% of men agreed to sleep with a stranger who showed interest in them. If men and women both want to reproduce, why do they have such different approaches toward sex?

Man walking with his girlfriend and turning to look at another woman while his girlfriend looks horrified.
Men are more into casual sex because their biology allows them to. Producing offspring never costed the males as much as females, so women are more sexually selective. (Image: Antonio Guillem/Shutterstock)

Men and women have scientifically proven differences, sometimes much smaller than people expect, due to biology, culture, and evolution. One significant difference is in their view of casual sex. A meta-analysis of many studies showed that men are much more likely to sleep with a stranger casually. No research, in any country, has ever shown that women are more casual about sex than men.

This is a transcript from the video series Understanding the Mysteries of Human Behavior. Watch it now, Wondrium.

How Big is the Difference?

A young man offering a bunch of pink tulips to a young woman.
Women are much more careful choosing a partner because of reproductive constraints and parental investment. (Image: Rock and Wasp/Shutterstock)

A few studies were conducted on college students, where an attractive researcher approached people of the other sex and said, “I’ve been noticing you around campus, and I find you very attractive.” And then the researcher asked one of three things: Would you go on a date with me?; Would you go back to my apartment with me?; or Would you go to bed with me?

Results showed that about 50% of both sexes agreed to go on a date. The difference showed up when it came to casual sex: not even one woman agreed, while 70% of the men did. There might be social and cultural reasons for this difference as well, but regardless of culture, women are more careful in choosing sexual partners.

Learn more about what makes relationships succeed or fail.

Biological Differences

Did men and women with more offspring differ in how they approached sex during millions of years of evolution? Evolutionary biologists say yes. Males and females of many species have different sexual behaviors. Reproductive constraint is the first biological difference.

Biologically, women have a limited number of reproductive years and can normally have one child at a time. On the other hand, men can father many children at the same time, and aging does not influence their reproduction capabilities that much.

The second biological difference is parental investment. Women have to invest much more biologically, i.e., pregnancy, feeding, etc., while men can have children at almost no cost. Thus, a woman has to be careful not to invest so much in a child that will not survive. This includes the choice of the mate as well.

Careful Women and Careless Men

Women who chose mates more carefully had a higher chance of producing offspring that survived longer. Hence, careful genes passed on through evolutionary history to the next generations. At the same time, women who had the wrong choices lost their reproductive chances, and their careless genes became extinct.

On the other hand, men who were less choosy could produce more offspring, and their genes survived to date. What else affects sexual selectiveness?

Personal Characteristics

An international study conducted in 37 cultures and six continents, with almost 10,000 participants, showed that both men and women value certain things. The first shared characteristic is being kind and understanding. Second, everyone wants a rather “intelligent and capable” partner. Not necessarily astonishingly smart, but no one wants an incompetent partner.

Older man holding hand of younger woman across a restaurant table.
While there were some characteristics that both men and women cared about, women cared about a man’s access to resources as well. (Image: Motortion Films/Shutterstock)

After these, men and women show interest in different things. Men prefer younger women because biologically, they are more capable of having children. This is evident in the average married couples as well. Perhaps, our ancestors who preferred younger female mates succeeded more in producing offspring with younger females, so the genes of preferring younger women survived.

Learn more about what makes people happy.

Women’s Preferences

Women, on the other hand, prefer a man who has more resources: a house, a car, money, social status, and power. As mentioned before, finding a willing and fertile man was never much of a challenge for a woman. Thus, fertility is almost a granted characteristic with male partners, but women want a man with other characteristics that would help them produce more competent children that can survive.

From an evolutionary point of view, perhaps women who mated with more powerful males with more resources, at any level, had a higher chance of supporting their offspring in survival. In none of the 37 cultures did men say that wealth and status are more important in a mate than women did. Women also put more emphasis on a man’s ambition and industriousness.

Conclusively, men can care less about partners due to biological and cultural reasons, and casual sex becomes a more reasonable option for them.

Common Questions about Casual Sex

Q: Do men and women practice casual sex equally?

No. Casual sex is more a male practice. Studies show that the difference between men and women is significant in this aspect.

Q: Why are men more casual about sex than women?

For evolutionary reasons, men practice casual sex more easily than women. It is more difficult for a male to get picked for mating, and almost all females are capable of reproducing. Thus, humans’ male ancestors would mate with any willing female partner.

Q: Why are women picky choosing a partner for sex?

Unlike men, women assess a man’s resources to father children and support them as well. All males are fertile almost life-long, so females look for other capabilities and usually avoid casual sex.

Q: How does reproductive constraint affect sexual behavior?

Reproductive constraints make a woman choose mating partners more carefully to make sure her offspring survives into adulthood. Thus, it has made women more sexually selective than men, which explains why women do not practice casual sex as much as men do.

Keep Reading
Evolutionary Psychology and Fundamental Human Needs
Analyzing Gender Differences in Psychology
Evolution and Psychology: A Mutual Relationship