Facial symmetry refers to bilateral symmetry of the face, in which, according to Merriam-Webster, features are arranged on opposite sides in such a way that, if divided, each side would be an identical half.
Imagine a dotted line down the center of a face: the more symmetrical a face, the more like mirror images the right and left sides of the face will be.
Survival of the Fittest
Animals prefer biological symmetry when seeking a mate, assert D.W. Zaidel and J.A. Cohen, researchers from the Department of Psychology at UCLA. While symmetry is associated with high physical fitness and genetic quality, asymmetry is associated with susceptibility to disease and parasites.
However, humans are different. Human brains are asymmetrical; babies are attracted to faces with small asymmetries, and facial asymmetry and attractiveness aren’t necessarily mutually exclusive.
Symmetry isn’t the only factor in determining beauty, according to Psychology Today. Others include averageness of features–those that are closer to the population average rather than extreme–and secondary sexual characteristics, such as prominent brows, cheekbones and jaws, and thinner cheeks for men; high foreheads, big eyes, full lips and small chins for women.
Faces can even be too symmetrical. Symmetrical faces created by reflecting half the face in a mirror were considered less attractive because abnormal features were exaggerated, says the Evolutionary Biology Research Group (EBRG) at the School of Animal Biology, Australia.
Asymmetry in human faces has been associated with emotions, say Zaidel and Cohen. The EBRG asserts when people are asked to portray an emotion, they’re more likely to do so on the left side of the face, and when asked to hide an emotion, do so on the right.
Perhaps this is why babies are more drawn to faces with a bit of asymmetry, and why too perfectly symmetrical faces may not be seen as attractive as they may come off as devoid of emotion.
Men and Women
Facial symmetry may be more attractive in men than in women, according to the Behavioral Biology Group, School of Biological Sciences, U.K. Because attractive men may already have enhanced secondary sexual characteristics–pronounced brow, cheekbones and jawline–any asymmetry may be more pronounced.
In addition, women may be more sensitive to symmetry when choosing a mate: a man with facial symmetry means babies with facial symmetry, which in turn means healthier babies.
Abnormalities in facial features, say Zaidel and Cohen, have been associated with neurological disorders like Down and Williams Syndromes. More subtle abnormalities have been seen in schizophrenics.
A 2009 study from psychologists at the University of Edinburgh suggested that men with more symmetrical faces were less likely to lose their cognitive abilities later in life.
References and ResourcesMerriam-Webster: Bilateral symmetry
The Face, Beauty, and Symmetry
Psychology Today: Is beauty only skin deep?
Are human preferences for facial symmetry focused on signals of developmental instability?
Asymmetry and human facial attractiveness