Stoddard assembled composites of members of the National Academy of Sciences and of the 1883 and 1884 graduating classes of Smith College. A cognitive theory emphasizes the role of prototypes in understanding how a person processes information. A prototype is an abstract, cognitive representation that reflects the best example of a category of objects or events, and it often is defined as the central tendency or the averaged members of the class of examples. For example, an average sized dog, neither very large nor very small, is usually represented as the prototypic dog in the human mind. So a dog that represents the average of all dogs would be the prototypic dog and a face that represents the average of all faces in the population would be the prototypic face.
Studies even show that young infants can average incoming stimuli to form a prototype.
The field of evolutionary biology suggests that perhaps innate, built-in mechanisms account for these preferences for attractive faces. In the most common form of natural selection, called normalizing or stabilizing selection, evolutionary pressures operate against the extremes of the population and in favor of characteristics representing the average or central tendency of the population. Thus average values of characteristics shaped by normalizing selection are preferred in the population. According to this view, individuals with average population characteristics should be less likely to carry harmful genetic mutations than individuals with extreme population characteristics. In fact, evolutionary biologist Donald Symons has proposed an innate mechanism of perception that detects the population mean of anatomical features.