Two sides to every face: Signalling functions of facial asymmetry

Highly symmetrical faces are frequently perceived as more attractive than less symmetrical faces. This has been attributed to fluctuating asymmetry being perceived as a sign of developmental instability. Some studies, however, have failed to find a relationship between facial asymmetry and actual health, casting doubt over this interpretation. Previous investigations, however, have failed to properly differentiate between fluctuating facial asymmetry and the systematic structural laterality seen in the human face. Patterns of facial laterality differ systematically between the sexes, as well as between individuals, and likely serve their own signaling purposes, unrelated to developmental stability. Across 7 studies structural facial asymmetry is shown to be sexually dimorphic, and to positively impact on ratings of attractiveness, trustworthiness, and health. This contrasts with fluctuating asymmetry, which impacts negatively on these traits. Geometric-morphometric analyses reveal that patterns (as opposed to levels) of asymmetry can also predict substantial variance in self-report Dark Triad personality traits.