Investigating facial correlates of dominance and trustworthiness : their biological underpinnings and perceptual properties

Abstract

Information conveyed by the face can be used in social encounters to make fast decisions about another person. Recently, a new model of face perception has been postulated (Oosterhof & Todorov, 2009) suggesting that there are two basic judgements that underlie person evaluations from faces: dominance and trustworthiness. But on the basis of which cues are these judgements made, and do these cues have biological validity? In this thesis I investigate two putative facial cues to dominance and trustworthiness; namely, facial width-to-height ratio (fWHR) and skin yellowness. In men, fWHR has previously been linked to aggressive and dominant behaviour as well as the perception of these traits. Here I show that a more positive dominance related trait (achievement striving) is also related to this metric, indicating a general association of fWHR to dominance rather than simple aggression. Furthermore, I explore the biological underpinnings of this metric by showing 1) that contrary to initial findings and predictions fWHR is not sexually dimorphic, and 2) that fWHR is associated with testosterone, indicating a physiological link between appearance and behaviour. Additionally, I extend current work on fWHR by showing that it acts as a cue to dominance not only in humans but also in non-human primates. The second part of the current thesis firstly identifies skin yellowness as a novel cue used in trustworthiness judgement. It shows that this putatively carotenoid induced cue to current health is not only employed in mate choice context but may also play an important role in other social context and in judgements of who poses an adequate partner for social interactions. Secondly, I show that skin yellowness is inversely related to testosterone levels in men, showing for the first time an association between this carotenoid induced signal and testosterone in humans thereby extending previous work in birds.