In physical attractiveness studies, averageness is a characteristic of physical beauty in which the average phenotype (outward appearance) of the individual is found to be most attractive. The majority of averageness studies have focused on photographic overlay studies of human faces, in which images are morphed together.
A possible evolutionary explanation for averageness is koinophilia, in which sexually-reproducing animals seek mates with average features because extremes may indicate disadvantageous mutations. Like-attracts-like is not a workable explanation, as it would result in assortative mating rather than averageness.
Francis Galton, cousin of Charles Darwin, devised a technique called composite photography, 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. Galton's hypothesis was that certain groups of people may have common facial characteristics. To test the hypothesis, 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. The resultant “averaged” faces did little to allow the a priori identification of either criminals or vegetarians, failing Galton's hypothesis. However, unexpectedly Galton observed that the composite image was more attractive than the component faces. Galton published this finding in 1878, and also described his composite photography technique in detail in Inquiries in Human Faculty and its Development.
This phenomenon is now known as "averageness-effect", that is highly physically attractive tend to be indicative of the average traits of the population.
Despite the novelty of these findings, Galton and Stoddard's observations were forgotten for over a century.
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 32-composite face was the most visually attractive of all the faces.
Many studies, using different averaging techniques, including the use of line drawings and face profiles, have shown that this is a general principle: average faces are consistently more attractive than the faces used to generate them. Furthermore if a female composite (averaged) face made of 32 different faces is overlain with the face of an extremely attractive female model, the two images often line up closely, indicating that the model's facial configuration is very similar to the composite's. See, for example, the illustration of Jessica Alba on the left.
This principle transcends culture. For instance, Coren Apicella and her co-workers from Harvard University created average faces of an isolated hunter-gatherer tribe of 1,000 in Tanzania, Africa, the Hadza people. Hadza people rated the averaged Hadza faces as more attractive than the actual faces in the tribe. While Europeans also rated average Hadza faces as attractive, the Hadza people expressed no preference for average European faces. Apicella attributes this difference to the wider visual experiences of the Europeans, as they had been exposed to both Western and African faces. Thus the indifference of the Hadza towards average European faces could have been the result of lacking the European norm in their visual experience. These results suggest that the rules for extracting attractive faces are culture-independent and innate, but the results of applying the rules depend on the environment and cultural experience.
That the preference for the average is biological rather than cultural has been supported by studies on babies, who gaze longer at attractive faces than at unattractive ones. Furthermore, Mark Stauss reported that 10-month-old children respond to average faces in the same way as they respond to attractive faces, and that these infants can extract the average from simply drawn faces consisting of only 4 features. Adam Rubenstein and coworkers showed that already at six months of age, children not only treat average faces the same as they treat attractive faces, but they are also able to extract the central tendency (i.e. the average) from a set of complex, naturalistic faces presented to them (i.e. not just the very simple 4-features faces used by Strauss). Thus the ability to extract the average from a set of realistic facial images operates from an early age, and is therefore almost certainly instinctive.
Despite these findings, David Perrett and his colleagues found that both men and women considered that a face averaged from a set of attractive faces was more appealing than one averaged from a wide range of women's faces. When the differences between the first face and the second face were slightly exaggerated the new face was judged, on average, to be more attractive still. The three faces are difficult to distinguish one from the other, although close examination shows that the so-called "exaggerated face" looks slightly younger than the average face (composed of women's faces aged 22–46 years). Since the same results were obtained using Japanese subjects and viewers, these findings are probably culture-independent, indicating that people generally find youthful average faces sexually the most attractive.
Potential evolutionary explanations
Koinophilia is an evolutionary hypothesis which proposes that mate-seeking animals preferentially chose individuals with a minimum of unusual features. Koinophilia intends to explain the clustering of organisms into species and other issues described by Darwins Dilemma. The koinophilia hypothesis predicts that sexual creatures should avoid individuals with unusual and mutant features, both physical and behavioural – explaining why what humans determine to be a beautiful face contains no extreme features. This is advantageous because most mutations that manifest themselves as changes in appearance, functionality or behavior, are disadvantageous.
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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. ... Celebrities whose faces are in perfect proportion include Jessica Alba, Liz Hurley and Shania Twain... Professor Kang Lee, of the University of Toronto, said: "...Our study proves that the structure of faces also contributes to our perception of facial attractiveness."
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- model's facial configuration is very similar to the composite's facial configuration
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