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Female faces are regarded as more attractive than male ones, a large study involving 12,000 people around the world has found. Surprisingly, women are even more likely than men to rate other women’s faces as more attractive.

“When we look at the rater sex, we see that the preference for female faces is much stronger for female raters,” says at the Max Planck Institute for Empirical Aesthetics in Germany.

In most mammals and birds, it is males that evolve features that make them attractive to the opposite sex, Wassiliwizky says. For instance, male mandrill baboons have vivid red and blue faces.

“Females are usually the choosy sex,” he says. “This is the mechanism that made males look more flamboyant.”

But as biologists from Charles Darwin onwards have noted, humans seem to be unusual in regarding females as “the fairer sex”.

“There has been a very long discussion since the 19th century on why these sex roles are reversed for humans, but strikingly it was never put to empirical test,” Wassiliwizky says.

He realised that he could check whether this assumption was correct by using the raw data from studies of facial attractiveness done for other purposes. For instance, one of the studies his team used data from looked at whether emotions affect facial attractiveness.

Most of the data analysed comes from studies that specifically recruited heterosexual volunteers to rate pictures of faces, Wassiliwizky says. The analysis does include ratings from a few volunteers who identified as lesbian, gay, bisexual or transgender, but the numbers are too small from which to draw any statistically significant conclusions.

The preference for female faces seems to cross national and cultural boundaries, with the team finding a “moderate to large” effect in all regions of the world except sub-Saharan Africa, and in all ethnic groups except those who identified as African.

The reason female faces are rated as more attractive could be to do with the physical differences between the sexes, Wassiliwizky says, but it is also possible that simply knowing a person is female or male changes how people rate their attractiveness.

By comparing people’s ratings with how feminine or masculine the features of the faces they rated were, the team concluded that two-thirds of the preference for female faces is down to physical differences, with a third down to knowing the sex.

But why do women rate other women as more attractive? “Women might show solidarity to each other, or appreciate each other’s beauty more,” Wassiliwizky speculates.

As for why women rate men even lower than men rate other men, women might be embarrassed to admit attraction, he suggests. “They know the data that they type into the computer are scrutinised, so maybe they don’t feel comfortable with that.”

Or maybe women are trying to work out what men’s personalities are like from their faces, which affects their ratings. Wassiliwizky says future studies should be more specific and ask, “How much do you feel physically attracted to this person?” instead of, “How attractive is this face?”

“The paper is very thorough in demonstrating a gender difference in attractiveness, covering many image sets and cultures,” says at the University of Bath, UK. “Researchers have long noted, however, that attractiveness is not just about choosing a mate.”

“The metanalytic study robustly confirms the existence of the ‘gender attractiveness gap’,” says at Charles University in the Czech Republic.

Kleisner’s team has found that , with some populations in Africa having the least sexual dimorphism in faces. That might help explain the lack of a significant effect there, he says.

Local standards of beauty can also differ markedly from global norms, Kleisner says. “A major limitation of the study is its lack of sensitivity to the specific aesthetics of African beauty.”

It is also possible studies based on the whole body would come to different conclusions. “We don’t know, to be honest,” Wassiliwizky says. No comparable studies have been done looking at whole-body attractiveness, he says.