Bornean orangutans (Pongo pygmaeus) show an attentional bias toward a male secondary sexual trait

Abstract

Visual attention mechanisms help organisms prioritize evolutionarily relevant stim-uli, like threats and mating opportunities. Individuals may, therefore, attend to specificfacial features. In humans, it has consistently been shown that secondary sexual traitsand attractive faces capture and hold attention. By contrast, evidence for such biasesin nonhuman primates, especially great apes, remains scarce. To address this gap, weconducted two eye-tracking experiments with four zoo-housed Bornean orangutans(Pongo pygmaeus), a species characterized by extreme sexual dimorphism. In bothexperiments, we found that orangutans exhibited an attentional bias toward fullyflanged males, a sexually dimorphic trait of some adult males. They not only lookedlonger at flanged males but were also more likely to immediately fixate on them. Thissuggests that great ape cognition has been shaped by sexual selection in a similar fash-ion to humans, where attentional biases toward masculine and attractive faces arewell-documented. At the same time, we cannot rule out the possibility that individualsattended more to flanged males due to their potential threat to both sexes. Neverthe-less, by demonstrating attentional attunement to a secondary sexual trait, our findingscontribute to the growing understanding of how sexually selected features influencecognition in nonhuman primates