Inconsistencies among studies investigating the relationship between facial beauty and symmetry may stem from divergent methodologies and approaches. Studies that have used normal, head-on photographs and created symmetrical left–left and right–right faces have reported a weak relationship between beauty and symmetry (Knowner, 1996 and Samuels et al., 1994) whereas studies that manipulated photographs through morphing or digital smoothing have reported a strong relationship (Grammer and Thornhill, 1994 and Rhodes et al., 1998). Small infants, for example, are more interested in beautiful faces than they are in symmetrical faces (Samuels et al., 1994) and this suggests that from birth the human brain is neuronally wired to attend to features related to beauty rather than to features related to symmetry in faces. Similarly, left–left and right–right faces are perfectly symmetrical and they have been found to be less attractive than the original faces giving rise to these composites (Knowner, 1996). Together, the findings on this issue suggest that in humans symmetry and attractiveness are not one and the same.Brain Cogn. 2005 Apr;57(3):261-3.
Appearance of symmetry, beauty, and health in human faces.
Zaidel DW et al.
Symmetry is an important concept in biology, being related to mate selection strategies, health, and survival of species. In human faces, the relevance of left-right symmetry to attractiveness and health is not well understood. We compared the appearance of facial attractiveness, health, and symmetry in three separate experiments. Participants inspected front views of faces on the computer screen and judged them on a 5-point scale according to their attractiveness in Experiment 1, health in Experiment 2, and symmetry in Experiment 3. We found that symmetry and attractiveness were not strongly related in faces of women or men while health and symmetry were related. There was a significant difference between attractiveness and symmetry judgments but not between health and symmetry judgments. Moreover, there was a significant difference between attractiveness and health. Facial symmetry may be critical for the appearance of health but it does not seem to be critical for the appearance of attractiveness, not surprisingly perhaps because human faces together with the human brain have been shaped by adaptive evolution to be naturally asymmetrical.