Anthony C. Little, Symmetry Is Related to Sexual Dimorphism in Faces: Data Across Culture and Species, PLoS ONE 3(5): e2106. doi:10.1371/journal.pone.0002106 (May 8, 2008)
High and low symmetry composite faces for macaques, Europeans, and Hadza.
Here we show that measurements of symmetry and sexual dimorphism from faces are related in humans, both in Europeans and African hunter-gatherers, and in a non-human primate. Using human judges, symmetry measurements were also related to perceived sexual dimorphism. In all samples, symmetric males had more masculine facial proportions and symmetric females had more feminine facial proportions.
Our findings support the claim that sexual dimorphism and symmetry in faces are signals advertising quality by providing evidence that there must be a biological mechanism linking the two traits during development. Such data also suggests that the signalling properties of faces are universal across human populations and are potentially phylogenetically old in primates.