Perceptions of facial trustworthiness and dominance modulate early neural responses to male facial sexual dimorphism

Sexual selection may have shaped the evolution of cognitive mechanisms to assess dominance and trustworthiness among anonymous conspecifics. We tested the hypothesis that masculine facial morphology and beardedness modulate early P100, N170, P200 and N250 event related potentials (ERP) components using electroencephalography (EEG) during judgments of male facial dominance and trustworthiness. We found that facial hair drove early P100 neural effects while facial masculinity drove an N170 effect during perceptions of dominance. For perceptions of trustworthiness, there was a significant N170 peak for bearded over clean-shaven faces while no significant effects were observed when judging facial masculinity. Clean-shaven faces exerted significant effects over bearded faces for P200 amplitudes for dominance and trustworthiness perceptions. The only significant N250 amplitudes occurred for beardedness over clean-shaven faces when judging trustworthiness. There were no effects of facial masculinity on any ERPs when faces were bearded, supporting previous research demonstrating that facial hair may mask sexually dimorphic structural facial traits. Masculine faces augmented judgments of dominance and trustworthiness over less masculine faces. Likewise, bearded faces enhanced dominance and trustworthiness judgments over clean-shaven faces. Our findings suggest facial masculinity activates neural responses involved in face processing when judging assertiveness and status seeking involved in same-sex competition, but not socially affiliative attributes prioritised in more communal behaviours. In contrast, facial hair acts as a low-level visual feature that rapidly communicated dominance and latterly communicated trustworthiness, suggesting a role of competence for facial hair when assessing male sociosexual attributes.