One-night stands happen, and are fairly common depending on who you ask and where they live. However, one element about these short-lived encounters transcends religious, cultural, and ethnic differences: more women regret participating in them, and more men regret passing them up. We may chalk it up to ingrained sexism, but one study suggests there may be a deeper evolutionary purpose behind this worldwide trend.

The study, published online in Evolutionary Psychology, revealed that a larger proportion of women than men regretted the last time they had casual sex. Based on a survey of 263 Norwegian students aged 19 to 37, around 35 percent of women regretted their last one-night stand, compared to only 20 percent of men. In addition, about 30 percent of women in Norway reported that they were happy about their most recent casual sex experience, compared to over 50 percent of the men. On the other hand, more men expressed regret at having declined a recent one-night stand opportunity. An overwhelming 80 percent of women expressed happiness at saying no to their last casual sex offer, but only 43 percent of men felt the same.

Read: Penis Size Matters For One-Night Stands, But Not Long-Term Relationships

Although societal pressures on women may explain the differences in post-sex regret, the research was conducted in Norway, which is widely held as one of the most sexually liberated and gender equal nations in the world. In addition, fewer women reported orgasming in their last sexual experience than men, and this could shape women's attitudes. One study from 2014 showed that women prefer men with bigger penises for one-night stands for exactly that reason, while opting for more humbly hung men for husbands. However, the researchers explained that this also was only part of a bigger picture.

"Men enjoy casual sex considerably more, but this doesn't explain the gender difference in regret, because gender is the most important influencing factor for both orgasm probability and sexual regret after casual sex," explained Professor Leif Edward Ottesen Kennair, a researcher involved with the study, in a recent statement.

So if it’s not orgasm or societal expectations, what could it be? According to the researchers, it may be based on evolutionary pressure that caused men and women to value different aspects of a sexual experience. Women value quality in a sexual partner whereas men value quantity of sex.

These sexual drives are innate, and most of us are not even consciously aware that they exist. In the game of evolution, the goal is always the same: Have many strong offspring to pass on your precious genes. For men, having sex with many women has long rewarded them with a plethora of offspring. Theoretically, it did not matter if all these children survived to adulthood, as long as the majority did. Women, on the other hand, heavily invest in their offspring. For them, the odds of having more children survive into adulthood was improved by choosing a mate who would share the responsibilities of child rearing.

Though we are no longer slaves to the elements of disease, disasters, and famine, these rules are still engraved in our psychology, and play a role in our sexual choices and sexual satisfaction. Women are more likely to regret a sexual experience the morning after when they realize they have chosen an unsuitable man. Men, on the other hand, are simply glad to have been given the opportunity to have spread their seeds.

"Many social scientists expect that in sexually egalitarian cultures such as Norway, these sex differences would disappear. They do not. This fact makes the findings on sex differences in sexual regret in modern Norwegian people so fascinating scientifically," explained evolutionary psychologist, Dr. David Buss in a statement.

Source: Ottesen Kennair LE, Bendixen M, Buss DM. Sexual Regret: Tests of Competing Explanations of Sex Differences. Evolutionary Psychology. 2017

See Also:

Most Women Think Love And Sex Should Go Together; Is It More Fulfilling Than A One-Night Stand?

Casual Sex Lowers Depression And Anxiety For Those Who Love It