In attractiveness studies, averageness is one of the characteristics of physical beauty in which the average phenotype, i.e. outward appearance, of the individual theoretically characterizes averaged genotypes, thus indicating health and fertility. The majority of averageness studies and theories have to do with photographic overlay studies, in which images are morphed together. Other factors involved in measuring attractiveness are symmetry, youthfulness and similarity (like-attracts-like.)
In 1883, Francis Galton, cousin of Charles Darwin, devised a technique called composite photography, described in detail in Inquiries in Human Faculty and its Development, which he believed could be used to identify 'types' by appearance, which he hoped would aid medical diagnosis, and even criminology through the identification of typical criminal faces. In short, he wondered if certain groups of people had certain facial characteristics. To find this answer, he created photographic composite images of the faces of vegetarians and criminals to see if there was a typical facial appearance for each. Galton overlaid multiple images of faces onto a single photographic plate so that each individual face contributed roughly equally to a final composite face. While the resultant “averaged” faces did little to allow the a priori identification of either criminals or vegetarians, Galton observed that the composite image was more attractive than the component faces. Similar observations were made in 1886 by Stoddard, who created composite faces of members of the National Academy of Sciences and graduating seniors of Smith College. This phenomenon is now known as "averageness-effect", that is highly physically attractive tend to be indicative of the average traits of the population.
In 1990, one of the first computer-based photographic attractiveness rating studies was conducted. During this year psychologists Langlois and Roggman wanted to systematically examine whether mathematical averageness is linked with facial attractiveness. To test this, they selected photographs of 192 male and female Caucasian faces; each of which was computer scanned and digitized. They then made computer-processed composites of each image, as 2-, 4-, 8-, 16-, and 32-face composites, averaged by pixel. These faces, as well as the component faces, were rated for attractiveness by 300 judges on a 5-point Likert scale (1 = very unattractive, 5 = very attractive). The results showed that the 32-composite face was the most visually attractive of all the faces.
Work on isolated populations suggest that preferences for averageness appear to be universal. In addition, while isolated people prefer average faces from their own race, they do not show any preference for average faces of other races to which they are not exposed. This makes sense since they should have no knowledge of what an average face looks like. This suggests that it is averageness alone, that is making a face attractive rather than some other artifact that results from the averaging techniques.
It makes biological sense that sexual creatures should be attracted to mates sporting a predominance of common or average features, as opposed to extraordinary features. Natural selection results, over the course of generations, in beneficial (or "fit") features replacing their disadvantageous counterparts. Thus, natural selection causes beneficial features to become increasingly more common with each generation, while the disadvantageous features become increasingly rare. A sexual creature, therefore, wishing to mate with a fit partner, would be expected to avoid individuals sporting rare, unusual, peculiar, or unique features (many of which are likely to be due to mutations), while being especially attracted to those individuals displaying a predominance of common or average features. Thus, in a face, the nose must be neither too long or too short, too wide or too narrow, the eyes too wide apart or too close together, the forehead too high or too low, or the chin too prominent or too receding: in other words, a beautiful face contains no extreme features. This is known as "koinophilia".
Koinophilia is predicated on the notion that evolution is something that is imposed on creatures or species. It is not anything that they "plan", "desire", "strive for" or can "prepare for". Thus it is not the "desire" (in any sense in which this word can be interpreted) of cheetah to evolve greater running speed, as running faster is likely to bring with it a higher toll in injuries, and metabolic stresses. The running speed of cheetahs is almost certainly subject to stabilizing selection, as would be the size of the wings of a bird, the layer of subcutaneous blubber of a whale or seal, or the hardness and rate of growth of the hooves of a zebra. The mutations that are the raw material for evolution are completely random events, and, except for the "silent mutations" which do not affect the functionality or appearance of the carrier, are, thus, in virtually every case, disadvantageous. It is therefore maladaptive to mate with a partner sporting extreme or unusual features. Not only is the chance that such an unusual feature might prove useful in the unpredictable future vanishingly small, there is also no known manner in which the "collection" of such mutations in an individual increases that individual's fitness (the production of more offspring and grand-offspring than the remainder of the population).
- BUSS, D.M. (1985) Human mate selection. American Scientist 37, 47-51
- Rhodes, Gillian; Zebrowitz, Leslie, A. (2002). Facial Attractiveness - Evolutionary, Cognitive, and Social Perspectives. Ablex. ISBN 1-56750-636-4.
- Fiona Macrae (27 December 2009). "Skin deep: Beautiful faces have Miss Average proportions". Daily Mail. Retrieved 2011-07-31. "All were head shots of the same person with different distances from eyes to mouth or between the eyes. She was at her most attractive when the space between her pupils was just under half, or 46 per cent, of the width of her face from ear to ear. The other perfect dimension was when the distance between her eyes and mouth was just over a third, or 36 per cent, of the overall length of her face from hairline to chin. ..."
- LANGLOIS, J.H. & ROGGMAN, L. (1990). Attractive faces are only average. Psychol. Sci. 1, 115-121
- LANGLOIS, J.H., ROGGMAN, L.A., MUSSELMAN, L., ACTON, S. (1991). A picture is worth a thousand words: Reply to "On the difficulty of averaging faces." Psychological Science 2, 354-357.
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- LANGLOIS, J.H., MUSSELMAN, L. (1995). The myths and mysteries of beauty. In D.R. Calhoun (Ed.), 1996 Yearbook of Science and the Future , pp. 40-61. Chicago: Encyclopædia Britannica, Inc.
- KALICK, S.M., ZEBROWITZ, L.A., LANGLOIS, J.H., JOHNSON, R.M. (1998). Does human facial attractiveness honestly advertise health? Longitudinal data on an evolutionary question. Psychological Science,9, 8-13
- RUBENSTEIN, A.J., LANGLOIS, J.H., ROGGMAN, L.A. (2002). What makes a face attractive and why: The role of averageness in defining facial beauty. In G. Rhodes & L.A. Zebrowitz (Eds.), Facial attractiveness: Evolutionary, cognitive, and social perspectives: Westport, CT: Ablex
- HOSS, R.A., LANGLOIS, J.H. (2003). Infants prefer attractive faces. In O. Pascalis & A. Slater (Eds.), The development of face processing in infancy and early childhood: Current perspectives pp. 27-38. New York: Nova Science Publishers.
- APICELLA, C.L., LITTLE,, A.C., MARLOWE, F.W. (2007) Facial Averageness and attractiveness in an isolated population of hunter-gatherers. Perception 36, 1813-1820
- KOESLAG, J.H. (1990). Koinophilia groups sexual creatures into species, promotes stasis, and stabilizes social behaviour. J. theor. Biol. 144, 15-35
- GOULD, S.J. (1980) Return of the Hopeful Monster. in The Panda's Thumb. p. 186-193. W.W. Norton, New York.
- Average Faces - Beauty Check