A tendency to prefer faces in which the eyes, nose, lips, and other features are close to the average of a population.1
People find faces that approximate their population average more attractive than faces that deviate from their population average. In this context, population refers to the group in which a person lives or was raised, and average refers to the arithmetic mean of the form, size, and position of the facial features. For example, when pictures of many faces within a population are combined (averaged) to form a single composite image, the composite image is similar to the facial configurations of professional models in that population.2
The most average facial appearance effect is likely the result of some combination of evolution, cognitive prototypes, and symmetry. Evolution by natural selection tends to select out extremes from a population over time. Therefore, it is possible that a preference for averageness has evolved as an indicator of general fitness. Cognitive prototypes are mental representations that are formed through experience. As people see the faces of other people, their mental representation of what a face is may be updated through a process similar to compositing. If this is the case, average faces pattern-match easily with cognitive prototypes, and contribute to a preference. Finally, average faces are symmetrical, and symmetry has long been viewed as an indicator of health and fitness. Asymmetric members of all species tend to have fewer offspring and live shorter lives—generally the asymmetry is the result of disease, malnutrition, or bad genes.3
The evolution of racial preferences among isolated ethnic groups demonstrates the influence of the most average facial appearance effect. Isolated groups form cognitive prototypes based on the faces within their population. When two of these groups first encounter one another, they invariably regard members of the unfamiliar group as strange and less attractive. The facial appearance of unfamiliar groups is perceived as less attractive because it is further from the average facial appearance of the familiar group. As the differences become more familiar, however, cognitive prototypes are updated and the definition of facial beauty changes.
The most average facial appearance for a population is an accurate benchmark of beauty for that population. There are other elements that contribute to attractiveness (e.g., smile versus scowl), but faces that are not average will not be perceived as attractive. Use composite images of faces created from randomly sampled faces of target populations to indicate local perceptions of beauty. Consider the use of digital compositing and morphing software to develop attractive faces from common faces for advertising and marketing campaigns, especially when real models are unavailable or budgetary resources are limited.
See also Attractiveness Bias, Baby-Face Bias, Mental Model, Normal Distribution, and Symmetry.