One of the leading aspects used to measure conventional attractiveness scientifically is facial symmetry. Typically, this is measured by manipulating an original photo of a person (we are all at least a little asymmetric, no person is perfectly symmetrical) into a perfectly symmetric version of their face. This manipulated, symmetric image is then presented to test subject along with the original photo. Subjects are then asked to indicate which face is more attractive, usually indicating the symmetrical version. (These findings have been replicated in multiple studies.) Though these results indicate that people prefer and perceive the more symmetric faces as attractive, there has been considerable debate about why this is.
There have been two theories of substance proposed by researchers to explain the preference for symmetrical faces:
The Evolutionary Advantage theory proposed that symmetrical faces are perceived as more attractive because the symmetry indicates good health in an individual. Everyone’s genes are designed to develop a face perfectly symmetrical, but as we grow, develop, and then age, disease, infections, and parasites cause imperfection in our appearance (asymmetry). Thus, those that have less asymmetry and imperfections, are perceived as having better and stronger immune systems to withstand the infections and parasites that occur naturally. So, symmetry is a good indicator of a person having good genes to pass on their offspring. Under the Evolutionary Advantage view of symmetric preferences, we have evolved to prefer symmetry and perceive it as attractive because over human history we have consistently and constantly preferred healthier individuals for mates. In sum, the Evolutionary Advantage view suggests that attraction to symmetric individuals reflects an attraction to healthy individuals who would be good mates.
The second theory to explain the preference for facial symmetry is Perceptual Bias. This theory suggests that the human visual system may be “hard wired” in a way that makes it much easier to process symmetrical stimuli than asymmetrical stimuli. If this is true, the ease of processing symmetrical stimuli would cause us to naturally prefer them to asymmetrical stimuli. Under this view, preferences for symmetrical faces would be no different than for any other object. So according to this, as well as preferring symmetrical faces, humans would also prefer more symmetrical objects of any kind. This has been supported as it has been found that people much prefer symmetrical pieces of abstract art and sculptures to asymmetrical ones.
Little and Jones (2003) did a study to investigate why people prefer symmetric faces to asymmetric ones, by testing and attempting to apply predictions from both the Evolutionary Advantage theory and Perceptual Bias. Previous studies found that the symmetric preference is stronger for attractiveness of opposite sex than same sex. Little and Jones found that the manipulated, symmetric faces were judged more attractive when shown the right way up, but not when the faces were inverted. These findings suggest that symmetry is more important in mate choice stimuli than in other stimuli, supporting the Evolutionary Advantage theory and presenting multiple difficulties for the Perception Bias theory (if symmetry of any kind was preferred then the more symmetrical face would have been indicated as more attractive both the right way up AND when inverted).
If anyone is interested in learning more, you can benefit from taking a class or just researching Penn State’s very own Dr. Mark Shriver, a geneticist, who conducts research in Brazil on facial symmetry. Though ongoing, Shriver’s research has measured thousands of Brazilian (and other ethnicities) faces in facial symmetry, judging their scientific attractiveness and therefore contributing the most evidence towards the idea that mixed race people are more attractive — in this case attraction is not subjective, it is purely measure with symmetry. Shriver teaches many higher level ANTH classes, but if anyone is interested, I suggest starting with ANTH 021 – Biological Anthropology.