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Facial symmetry is one specific measure of bodily asymmetry. Along with traits such as averageness and youthfulness it influences judgements of aesthetic traits of physical attractiveness and beauty.〔Grammer, K., & Thornhill, R. (1994). Human (Homo sapiens) facial attractiveness and sexual selection: the role of symmetry and averageness. Journal of comparative psychology (Washington, D.C. : 1983), 108(3), 233–42.〕 It is also associated with health and genetic fitness.〔Jones, B. C., Little, A. C., Tiddeman, B. P., Burt, D. M., & Perrett, D. I. (2001). Facial symmetry and judgements of apparent health Support for a “‘ good genes ’” explanation of the attractiveness – symmetry relationship, 22, 417–429.〕 Facial symmetry has been suggested as a possible physical manifestation of the 'big-five' personality traits.〔Fink, B., Neave, N., Manning, J. T., & Grammer, K. (2005). Facial symmetry and the “big-five” personality factors. ''Personality and Individual Differences'', 39(3), 523–529.〕 For example, it is found that extraversion and openness are strongly associated with the symmetry of the face.〔 Hormones such as testosterone and estrogen are believed to be associated with developmental processes and growth of facial features during puberty and as a result are hypothesized to be the cause for individual differences in the implications associated with facial symmetry.〔Gangestad, S., & Thornhill, R. (2003). Facial masculinity and fluctuating asymmetry. Evolution and Human Behavior, 24(4), 231–241.〕 Facial bilateral symmetry is measured via fluctuating asymmetry of the face comparing random differences in facial features of the two sides of the face that develop and accumulate throughout one's lifetime as a result of stressors.〔Penton-Voak, I. S., Jones, B. C., Little, a C., Baker, S., Tiddeman, B., Burt, D. M., & Perrett, D. I. (2001). Symmetry, sexual dimorphism in facial proportions and male facial attractiveness. Proceedings. Biological sciences / The Royal Society, 268(1476), 1617–23.〕〔Penke, L., Bates, T. C., Gow, A. J., Pattie, A., Starr, J. M., Jones, B. C., Perrett, D. I., et al. (2009). Symmetric faces are a sign of successful cognitive aging. Evolution and Human Behavior, 30(6), 429–437.〕 ==Facial symmetry== Facial symmetry has been shown to have an effect of ratings of attractiveness in human faces.〔〔 More symmetrical faces are perceived as more attractive in both males and females, although facial symmetry plays a larger role in judgments of attractiveness concerning female faces.〔Rhodes, G., Proffitt, F., Grady, J. M., & Sumich, A. (1998). "Facial symmetry and the perception of beauty." ''Psychonomic Bulletin & Review'', 5(4), 659–669.〕 A wide variety of methods has been used to examine the claim that facial symmetry plays a role in judgments of beauty. Blending of multiple faces to create a composite〔 and face-half mirroring〔Kowner, R. (1996). "Facial asymmetry and attractiveness judgment in developmental perspective." ''Journal of Experimental Psychology''. Human perception and performance, 22(3), 662–75.〕 have been among the techniques used. While studies employing the first method produced results that indicate that more symmetrical faces are perceived as more attractive, studies applying the later method have indicated that humans prefer slight asymmetry. Also studies show that nearly symmetrical faces are considered highly attractive compared to unsymmetrical ones, yet more specifically, people tend to find a face unattractive if a person has an unsymmetrical nose, and effect of unsymmetrical lips do not really affect people on judging attractiveness. The most conspicuous directional asymmetries are sometimes only temporary.〔"Symmetric Shape Deformation Considering Facial Features and Attractiveness Improvement" by Kim Jung-Sik, Shin Il-Kyu, Soo-Mi Choi, Dept. of Computer Science and Engineering, Vol. 16 No. 2 pp. 29–37, Sejong University〕 For example, during speech, most people (76%) tend to express greater amplitude of movement on the right side of their mouth. This is most likely caused by the uneven strengths of contralateral neural connections between the left hemisphere of the brain (linguistic localization) and the right side of the face.〔 Conclusions derived from face mirroring, however, have been called into question, because it has been shown that mirroring face-halves creates artificial features. For example, if the nose of an individual is slightly bent to the right side, then mirroring the right side of the face will lead to an over-sized nose, while mirroring the left side will lead to an unnaturally small nose. 〔Perrett, D. I., Burt, D. M., Penton-Voak, I. S., Lee, K. J., Rowland, D. a, & Edwards, R. (1999). "Symmetry and Human Facial Attractiveness." ''Evolution and Human Behavior'', 20(5), 295–307.〕 Evolutionary theorists in biology and psychology argue that more symmetric faces are preferred because symmetry is a possible honest sign of superior genetic quality and developmental stability.〔〔Scheib, J. E., Gangestad, S. W., & Thornhill, R. (1999). "Facial attractiveness, symmetry and cues of good genes." Proceedings. Biological sciences / The Royal Society, 266(1431), 1913–17.〕 However it is possible that high facial symmetry in an individual is not due to their superior genetics but due to a lack of exposure to stressors during development. This potentially confounding source of facial symmetry is not explored in the literature. The notion that facial symmetry is viewed by humans as an indicator of 'good genes' is supported by experiments demonstrating that more symmetrical faces are rated as healthier than less symmetrical faces.〔〔 Additionally, asymmetry can be fluctuated by increasing health challenges during growth. As a result, phenotypic quality and how well an individual's genome can fight disease and uphold normal development can be indicated by symmetry.〔 Alex Dodge 2012 left.jpg Alex Dodge 2012.jpg|Original Alex Dodge 2012 right.jpg Facial symmetry is also a valid marker of cognitive aging.〔 Progressive changes occurring throughout life in the soft tissues of the face will cause more prominent facial asymmetry in older faces.〔 Therefore, symmetrical transformation of older faces generally increases their attractiveness while symmetrical transformation in young adults and children will decrease their attractiveness.〔 Males with more symmetric faces in old age have higher intelligence and are more efficient at information processing than males with less symmetric faces. This is possibly due to the better genes leading to more resistance against stressors in life which is then reflected in less accumulated fluctuating asymmetry.〔 Non-scientific theories of attraction and symmetry abound. Symmetry of each face is evaluated by human brain via the facial recognition process. This fast and effective detection is difficult with computer programs.〔Chunyu L, Changshui Z, Fang W, Pingfan Y. "Principle () component analysis based symmetry detection." ''Acta Electronica Sinica'' 1999;27(5):25–8.〕〔Enquist M, Arak A. "Symmetry, beauty and evolution." ''Nature'' 2002;372: 169–72.〕 For instance, the faces that were considered to possess a strong aesthetic appeal were the ones where the conjunction of similar or corresponding facial features were, to some extent, contrasting. Likewise shared features echoism, proportions and similarity to people the person bonded to early in life (prima copulism) have been suggested as relevant. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「facial symmetry」の詳細全文を読む スポンサード リンク
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