Researchers found that women are really good at judging which men are only interested in short-term uncommitted relationships just by reading their faces. Apparently, men with longer faces, higher foreheads, longer noses, and larger eyes tend to be more open to casual sex, and women can pick up on this.

The team of researchers from Macquarie University in Australia embarked on this study starting from a debate about the mechanics of attraction in humans. According to evolutionary psychology, humans are attracted to healthy, fertile, and compatible potential mates. If such is the case, then humans must be able to read certain cues in our faces and bodies that reflect these desirable mating characteristics.

If humans can visually judge if someone is ‘hot’ or not, what other cues can they pick up that are evolutionarily important when selecting a mate? The Australian researchers hypothesized that being able to tell whether someone is interested in a monogamous relationship or casual sex could be the kind of information that humans may be able to extract from visual cues, such as facial traits.

With this in mind, they recruited 103 white individuals, both male and female, who had their portraits taken and had to complete a survey that assessed their level of sociosexuality (how open they are to casual, uncommitted sex). The researchers then associated the sociosexuality scores with facial shape characteristics in men, but not in women where no reliable association could be found.

In a subsequent study, these photos were shown to 65 heterosexual participants who were asked to assess the sociosexuality of the person of the opposite sex shown in the pictures. Interestingly, women’s perception of male sociosexuality matched the men’s self-reported sociosexuality scores, showing that women can predict some of men’s sexual desires and intentions from their faces. However, males were terrible at this task. Their perception of women’s sociosexuality did not match the women’s self-reported attitudes and behaviors towards casual sex.

Lastly, the researchers used the data gathered in the previous studies to make computer-generated pairs of portraits representing high- and low-sociosexuality faces. Participants correctly identified high-sociosexuality faces better than chance — yet again, just in men and not women.

It’s not clear what’s responsible for these observed effects. It may be that assessing whether a potential mate will stick around or not is much more important for women than men because sex (and pregnancy) is more costly.

The researchers suspect that the sociosexual orientation reflected in males’ faces may be due to testosterone, which leads to quite a bit more variation in facial features in men than seen in women. Men with higher testosterone tend to have more traditionally masculine faces (for example, a wider brow, a longer nose, and a wider distance between the eyes). High-testosterone men tend to be more attractive to women, but also tend to express more promiscuous tendencies.

However, this hypothesis cannot be tested because the study did not include testosterone measurements for the participants. As a caveat, the researchers caution that these findings shouldn’t be used as a license to make snap judgments about people’s personalities or intentions. Ultimately, the best test of a person’s character is getting to know them.

The findings appeared in the journal Evolution and Human Behavior.

This article originally appeared in July 2021.