New research suggests the shape of a person’s face could affect how aggressive they look.

The team measured the width-to-height ratio of over 17,000 passport images and asked people to rate how aggressive they looked. 

Faces that appeared more square were perceived to be more aggressive than those that were more oval-shaped, especially in young men.

Specifically, they looked at the facial-width-to-height ratio (FWHR) of 17,607 passport images of male and female faces across their lifespans.

The results suggest that found larger FWHR in males only in young adulthood, aligning with the stage most commonly associated with mate selection and intrasexual competition. 

However, the direction of dimorphism was reversed after age 48, with females recording larger FWHRs than males. 

The team then examined how natural variation in FWHR affected perceived aggressiveness. 

The relationship between FWHR and perceived aggressiveness was strongest for males at ages 27-33 and females at 34-61, with raters most sensitive to differences in FWHR for young adult male faces.

The full study is accessible here.