Wider-faced golden snub-nosed monkeys more aggressive, study finds

A research team from Northwest University in Xi'an, Shaanxi province, has confirmed that male golden snub-nosed monkeys with wider faces are not only more aggressive but also more likely to emerge victorious in physical confrontations, China Science Daily reported on Saturday.

Recently published in the journal Animal Behaviour, the findings stem from a three-year field study conducted in the Qinling Mountains in Shaanxi, where Zhang Pei, associate professor at Northwest University and lead author of the study, observed a habituated wild population. They captured standardized frontal facial photographs of 126 individual monkeys to calculate the facial width-to-height ratio, a metric widely studied in humans and animals for its association with dominance and competitive traits. They also documented 1,628 conflict events among 15 dominant males, recording every attack and outcome.

The results showed that adult males with higher facial width-to-height ratios, meaning those with generally wider faces, initiated significantly more aggressive interactions and won a greater proportion of their fights, even after the team controlled for confounding factors such as body weight and harem group size. Other factors, such as age and "first strike" advantage, also predicted winning.

"We speculate that the link between facial width-to-height ratio and aggressiveness and fighting ability is not unique to a particular species, but is likely a general pattern across primates," Zhang said.

Additionally, they discovered that wider faces did not function as a deterrent. Male monkeys did not adjust their attack decisions based on an opponent's facial shape; instead, their aggression was driven primarily by their own competitive capacity. This suggests that while facial width is a reliable indicator of fighting ability and aggressive inclination, it does not serve as a social signal that rivals use to deter opponents and avoid costly conflicts.