SYDNEY: Men with brown eyes have more trustworthy faces than men with blue eyes, according to a new study that proposes sexual selection of women in Europe about 10,000 years ago could be the cause.
Various facial traits, such as larger noses and higher set features, have previously been associated with perceived traits such as trustworthiness, dominance and attractiveness, which in turn can indicate political success or salary of the person. But this was the first study that looked at eye colour and perceptions of trustworthiness.
“Men with brown eyes tend to be perceived as more trustworthy than men with blue eyes,” concluded Karel Kleisner, from Charles University in Prague, Czech Republic, co-author of the story published in the journal PLOS One.
It’s not just the eyes
In the study, researchers in Prague showed a series of non-smiling photographs of 40 men and 40 women to 230 participants.
The participants rated men with brown eyes as more trustworthy than those blue eyes. Women were consistently rated as more trustworthy than men, though there was no significant link between eye colour and trustworthiness as there was in males.
The researchers then mapped the features of the faces, and found a correlation between eye colour and face shape in males: brown-eyed male faces had a bigger mouth, a broader chin, a bigger nose, and more prominent eyebrows positioned closer to each other than blue-eyes males. Blue-eyed males, on the other hand, have a more gracile facial structure.
“Our study shows that the relationship between eye color and facial structure is not accidental,” said Kleisner.
How did European people become so colourful?
The authors of the paper suggest that the correlation between face shape and eye colour could be due to sexual selection among early Europeans.
Study author and anthropologist Peter Frost, from the Université Laval in Quebec, Canada, first proposed in 2006 that hair and eye colour diversified among early Europeans through intense sexual selection of women for novel and bright colour traits, including blonde and red hair, and blue and green eyes. This occurred because in the European tundra, male hunters provided almost all the food and long-distance hunting caused more deaths among young men than women, leading to a surplus of women, he argued.
This process of selection could have linked sex to the hair and eye colours – for example, through sensitivity to estrogen during fetal development.
In this new study, the researchers “tentatively suggest that a combination of sex linkage and sexual selection is the most probable explanation for the reported [link] between brown eyes and trustworthylooking faces.”
“It may be that pre-natal exposure to estrogen is over-determined in women, that is, all women are fully exposed to estrogen before birth regardless of their eye color. In men, the increase in pre-natal exposure would be confined to blue-eyed individuals,” the researchers wrote.
Psychology and social science researcher Rachel Robbins from the University of Western Sydney, Australia, who was not involved in the study, said the results were surprising only in part. While the correlation between eye colour and trustworthiness was startling, face shape made more sense.
“Faces can convey a lot of important information and shape is usually considered to be most important for conveying who some one is, their sex, age, attractiveness and so on,” she said.
The paper in PLoS ONE: Trustworthy-Looking Face Meets Brown Eyes