She thinks friends, he thinks sex

Imagine the following scenario: a woman and a man are having a conversation. She is interested in the conversation, and is friendly, smiling and warm. He interprets her behavior as sexual interest.

Or maybe: a man is sexually attracted to a woman he has just met, and signals this in various ways. She thinks that he is just being friendly.

Recognize these situations? If so, you're not alone.

We misunderstand each other

In a recent study at the Department of Psychology at the Norwegian University of Science and Technology (NTNU), women reported that men often misinterpret their signals of friendliness as sexual interest. Conversely, the men in the study reported that women often misinterpret their signals of sexual interest as friendliness.

"The results are no surprise, seen from an evolutionary perspective," researcher Mons Bendixen explains. "The fascinating thing is that our results are identical to a study done in the USA, even though Norway is one of the most gender-equal, sexually liberal countries in the world."

In most areas of psychology, there is little to no difference between genders: mental capacity, intellectual achievements, food preferences - men and women are all more or less the same. But when it comes to reproduction and challenges related to finding a sexual partner, there are suddenly differences to be found.

Evolutionary psychology is the study of how the human mind has evolved, developed and adapted over time. One thing that evolutionary psychologists are specifically interested in is gendered sexual psychology between cultures and social groups. Seen through the lens of evolutionary psychology, we can better understand why men often wrongly assume that women who smile and laugh during conversation may want to sleep with them.

Men can't be picky

A man's ability to reproduce is all about seizing every opportunity. He has to spend both money and time on courtship, which still may not lead to sex. But it costs even more to not try, because then he won't be able to reproduce.

"A man's reproductive fitness, meaning the amount offspring he produces, is dependent on how many women he is able to make pregnant. But that's not how it works for women," Bendixen explains.

A woman can have sex with multiple men over a short period of time without producing any more children. So for men, it is a low-risk, potentially high-reward situation for men to have sex with women whenever the opportunity presents itself.

On the other hand, the cost is potentially great for a woman if she thinks that a man is more sexually interested than she is. A woman risks pregnancy, birth, nursing and raising the child, as well as lost oppotunities to reproduce with others. Across thousands of generations, women's psychology has evolved to set the bar higher, which means they need much clearer signals than men before they consider sex.