title: Symmetry is related to sexual dimorphism in faces: data across culture and species.
abstract: BACKGROUND
  Many animals both display and assess multiple signals. Two prominently studied traits are symmetry and sexual dimorphism, which, for many animals, are proposed cues to heritable fitness benefits. These traits are associated with other potential benefits, such as fertility. In humans, the face has been extensively studied in terms of attractiveness. Faces have the potential to be advertisements of mate quality and both symmetry and sexual dimorphism have been linked to the attractiveness of human face shape.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: School of Psychology, University of Stirling, Stirling, United Kingdom. anthony.little@stir.ac.uk
authors.forename: Anthony C
authors.initials: AC
authors.lastname: Little
authors.forename: Benedict C
authors.initials: BC
authors.lastname: Jones
authors.forename: Corri
authors.initials: C
authors.lastname: Waitt
authors.forename: Bernard P
authors.initials: BP
authors.lastname: Tiddeman
authors.forename: David R
authors.initials: DR
authors.lastname: Feinberg
authors.forename: David I
authors.initials: DI
authors.lastname: Perrett
authors.forename: Coren L
authors.initials: CL
authors.lastname: Apicella
authors.forename: Frank W
authors.initials: FW
authors.lastname: Marlowe
mesh_terms: D000818:Animals; D003469:Culture; D005145:Face / Q000033:anatomy & histology*; D005146:Facial Asymmetry / Q000235:genetics; D005260:Female; D006801:Humans; D008253:Macaca mulatta / Q000033:anatomy & histology / Q000502:physiology; D008297:Male; D012727:Sex Characteristics; D012725:Sexual Behavior; D012726:Sexual Behavior, Animal; D013045:Species Specificity