Facial symmetry

Last updated
Braus 1921 395.png
Braus 1921 396.png
While symmetrical faces (leftmost image) are perceived to be attractive, completely symmetric faces (a and b) are disconcerting and are not perceived as normal.

Facial symmetry is one specific measure of bodily symmetry. Along with traits such as averageness and youthfulness, it influences judgments of aesthetic traits of physical attractiveness and beauty. [1] For instance, in mate selection, people have been shown to have a preference for symmetry. [2] [3]

Contents

Facial bilateral symmetry is typically defined as fluctuating asymmetry of the face comparing random differences in facial features of the two sides of the face. [4] The human face also has systematic, directional asymmetry: on average, the face (mouth, nose and eyes) sits systematically to the left with respect to the axis through the ears, the so-called aurofacial asymmetry. [5]

Directional asymmetry

Directional asymmetry is systematic. The average across the population is not "symmetric", but statistically significantly biased on one direction. That means, that individuals of a species can be symmetric, or even asymmetric to the opposite side (see, e.g., handedness), but most individuals are asymmetric to the same side. The relation between directional and fluctuating asymmetry is comparable to the concepts of accuracy and precision in empirical measurements.

There are examples from the brain (Yakovlevian torque and spine, [6] and inner organs (see axial twist theory), but also from various animals (see Symmetry in biology).

Aurofacial asymmetry

Exaggerated schema of the aurofacial asymmetry as predicted by the axial twist theory. During embryology and development, the face elements (red) are predicted to move toward the center from the left, with respect to the mid-plane between the ears. Source: figure 1c of reference Face-schema aurofacial asymmetry.png
Exaggerated schema of the aurofacial asymmetry as predicted by the axial twist theory. During embryology and development, the face elements (red) are predicted to move toward the center from the left, with respect to the mid-plane between the ears. Source: figure 1c of reference

Aurofacial asymmetry (from Latin auris 'ear' and faciēs 'face') is an example of directed asymmetry of the face. It refers to the left-sided offset of the face (i.e. eyes, nose, and mouth) with respect to the ears. On average, the face's offset is slightly to the left, meaning that the right side of the face appears larger than the left side. The offset is larger in newborns and reduces gradually during growth. [8] [9]

Anatomy and definition

In contrast to fluctuating asymmetry, directional asymmetry is systematic, i.e. across the population it is systematically more often in one direction than in the other. It means that across the population a deviation is more often to one direction than to the other, i.e., there is a statistically significant bias to one direction. In case of directional asymmetry, most individuals of a species are asymmetric to the same side, even though some individuals can be symmetric, or even asymmetric to the opposite side (cf., e.g., handedness). The relation between directional and fluctuating asymmetry is comparable to the concepts of accuracy and precision in empirical measurements.

The aurofacial asymmetry is defined as the position of the face (mouth, nose and eyes) with respect to the mid plane of the axis through the ears. The asymmetry is expressed as an angle (degrees), i.e. by how many degrees facial landmarks (e.g. tip of the nose) or pairs of landmarks (e.g. inner corners of the eyes (endocanthions are rotated away from the mid plane between the ears. [8]

Magnitude across the face and development

Average aurofacial asymmetry in 200 adults. A. Red-shaded: significant asymmetry towards the left ear. B. The amount of asymmetry at the level of each arrow in panel A. Source: figure 2 of reference, and data from Aurofacial asymmetry.pdf
Average aurofacial asymmetry in 200 adults. A. Red-shaded: significant asymmetry towards the left ear. B. The amount of asymmetry at the level of each arrow in panel A. Source: figure 2 of reference, and data from

On average, the aurofacial asymmetry is slightly larger for the eyes than for the nose, as shown by the figure.

The gradual decrease of the aurofacial asymmetry with age until the beginning of adulthood. Source: figure 3 of reference on the basis of data from ref Age-relation for aurofacial asymmetry.png
The gradual decrease of the aurofacial asymmetry with age until the beginning of adulthood. Source: figure 3 of reference on the basis of data from ref

In humans asymmetric growth leads to a gradual reduction of the aurofacial asymmetry. [8] As shown in the graph, the asymmetry decreases from about 2° at birth to about 0.5° in adults.

Theory and evolution

The aurofacial asymmetry was discovered [8] after it was predicted by the axial twist theory. [7] According to the theory the facial asymmetry is related to the Yakovlevian torque of the cerebrum, asymmetric heart and bowels and the spine. It is predicted to be common in vertebrates, but this has never been tested.

The axial twist occurs in the early embryo. Shortly after the neurulation, the anterior head region makes a half-turn around the body axis in anti-clockwise direction (looking from tail to head), whereas the rest of the body (except heart and bowels) make a half-turn in clockwise direction. Since the axial twist is located between the ear-region and the forebrain-face-region, it is predicted that the face grows from the left to the midline, as is indeed the case.

Fluctuating asymmetry

Fluctuating asymmetry is the non-systematic variation of individual facial landmarks with respect to the facial midline, i.e., the line perpendicular to the line through the eyes, which crosses the tip of the nose and the chin.

A wide variety of methods have been used to examine the claim that facial symmetry plays a role in judgments of beauty. Blending of multiple faces to create a composite [1] [13] [14] and face-half mirroring [15] have been among the techniques used.

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. [16]

Attractiveness

Facial symmetry has been found to increase ratings of attractiveness in human faces. [1] [3] 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. [17]

While studies employing the composite faces produced results that indicate that more symmetrical faces are perceived as more attractive,[ citation needed ] studies applying the face-half mirroring technique have indicated that humans prefer slight asymmetry.[ citation needed ] Also, studies have shown that nearly symmetrical faces are considered highly attractive as compared to asymmetrical ones. [18] The symmetry of the nose seems to be more important than that of the lips.[ citation needed ]

Dynamic asymmetries

Highly conspicuous directional asymmetries can be temporary ones. [19] 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. [16]

Facial averageness vs. symmetry

Experiments suggest that symmetry and averageness make independent contributions to attractiveness. [20] [21]

Aging

Facial symmetry is also a valid marker of cognitive aging. [22] Progressive changes occurring throughout life in the soft tissues of the face will cause more prominent facial asymmetry in older faces. [16] Therefore, symmetrical transformation of older faces generally increases their attractiveness while symmetrical transformation in young adults and children will decrease their attractiveness. [16]

Personality and Big Five personality traits

Research indicates that facial symmetry is correlated with the 'big-five' model of personality. The five factors are:[ citation needed ]

A consistent finding is that facial symmetry is positively correlated with extraversion, indicating that individuals with more symmetric faces are also more extroverted. [23] [24] [25] More symmetrical faces are also judged to be lower on neuroticism but higher on conscientiousness and agreeableness (asymmetrical faces were rated as less agreeable than normal ones, but the more symmetrical were again rated as somewhat less agreeable than the normal). [26] More symmetrical faces are also more likely to have more desirable social attributes assigned to them, such as sociable, intelligent or lively. [25]

However, the relationship of facial symmetry and the 'big-five' personality model remains somewhat unclear with regard to neuroticism, openness, agreeableness and conscientiousness. Openness and agreeableness appear to be significantly negatively related to facial symmetry, while neuroticism and conscientiousness do not seem to be linked to facial symmetry. [23] With respect to trustworthiness it has been found that the facial muscles become imbalanced when lying. [27]

Evolution and sexual selection

Sexual selection is a theoretical construct within evolution theory. According to sexual selection, mate choice can have profound influence on the preferred features. Sexual selection can only influence features that potential mates can perceive, such as smell, audition (e.g. song) and vision. Such features might be reliable indicators of hidden fitness parameters such as a good immune system or developmental stability.

It has been argued that more symmetric faces are preferred because symmetry might be a reliable sign of such hidden fitness parameters. [28] 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, such as alcohol, during prenatal development. [12]

It has been found that more symmetrical faces are rated as healthier than less symmetrical faces. [3] [17] Indeed, facial symmetry was found to be positively associated with the perceived healthiness of the facial skin. [29] Also, facial asymmetry was found to be correlated with physiological, psychological and emotional distress. [30]

Some evidence suggests that face preferences in adults might be correlated to infections in childhood. [31]

See also

Related Research Articles

<span class="mw-page-title-main">Symmetry</span> Mathematical invariance under transformations

Symmetry in everyday life refers to a sense of harmonious and beautiful proportion and balance. In mathematics, the term has a more precise definition and is usually used to refer to an object that is invariant under some transformations, such as translation, reflection, rotation, or scaling. Although these two meanings of the word can sometimes be told apart, they are intricately related, and hence are discussed together in this article.

<span class="mw-page-title-main">Asymmetry</span> Absence of, or a violation of, symmetry

Asymmetry is the absence of, or a violation of, symmetry. Symmetry is an important property of both physical and abstract systems and it may be displayed in precise terms or in more aesthetic terms. The absence of or violation of symmetry that are either expected or desired can have important consequences for a system.

Interpersonal attraction, as a part of social psychology, is the study of the attraction between people which leads to the development of platonic or romantic relationships. It is distinct from perceptions such as physical attractiveness, and involves views of what is and what is not considered beautiful or attractive.

<span class="mw-page-title-main">Physical attractiveness</span> Aesthetic assessment of physical traits

Physical attractiveness is the degree to which a person's physical features are considered aesthetically pleasing or beautiful. The term often implies sexual attractiveness or desirability, but can also be distinct from either. There are many factors which influence one person's attraction to another, with physical aspects being one of them. Physical attraction itself includes universal perceptions common to all human cultures such as facial symmetry, sociocultural dependent attributes, and personal preferences unique to a particular individual.

<span class="mw-page-title-main">Symmetry in biology</span> Geometric symmetry in living beings

Symmetry in biology refers to the symmetry observed in organisms, including plants, animals, fungi, and bacteria. External symmetry can be easily seen by just looking at an organism. For example, the face of a human being has a plane of symmetry down its centre, or a pine cone displays a clear symmetrical spiral pattern. Internal features can also show symmetry, for example the tubes in the human body which are cylindrical and have several planes of symmetry.

<span class="mw-page-title-main">Fluctuating asymmetry</span> Form of biological asymmetry

Fluctuating asymmetry (FA), is a form of biological asymmetry, along with anti-symmetry and direction asymmetry. Fluctuating asymmetry refers to small, random deviations away from perfect bilateral symmetry. This deviation from perfection is thought to reflect the genetic and environmental pressures experienced throughout development, with greater pressures resulting in higher levels of asymmetry. Examples of FA in the human body include unequal sizes (asymmetry) of bilateral features in the face and body, such as left and right eyes, ears, wrists, breasts, testicles, and thighs.

<span class="mw-page-title-main">Asymmetric cut</span> Haircut

An asymmetric cut is a haircut in which the hair is cut in such a way that the hair does not have left-right symmetry and one side is cut or appears to be longer than the other. It is a versatile hairstyle with many subvariations. Usually it is a combination of two separate styles, one for each side.

David Ian Perrett FBA FRSE is a professor of psychology at the University of St Andrews in Scotland, where he leads the Perception Lab. The main focus in his team's research is on face perception, including facial cues to health, effects of physiological conditions on facial appearance, and facial preferences in social settings such as trust games and mate choice. He has published over 400 peer-reviewed articles, many of which appearing in leading scientific journals such as the Proceedings of the Royal Society of London Series B—Biological Sciences, Psychological Science, and Nature.

<span class="mw-page-title-main">Benedict Jones</span>

Benedict Jones is a research psychologist and lecturer at the University of Glasgow who studies the biological and social factors underlying face perception and preferences. He received his PhD from the University of St Andrews in 2005, where he studied with David Perrett.

The psychology of art is the scientific study of cognitive and emotional processes precipitated by the sensory perception of aesthetic artefacts, such as viewing a painting or touching a sculpture. It is an emerging multidisciplinary field of inquiry, closely related to the psychology of aesthetics, including neuroaesthetics.

In physical attractiveness studies, averageness describes the physical beauty that results from averaging the facial features of people of the same gender and approximately the same age. The majority of averageness studies have focused on photographic overlay studies of human faces, in which images are morphed together. The term "average" is used strictly to denote the technical definition of the mathematical mean. An averaged face is not unremarkable, but is, in fact, quite good looking. Nor is it typical in the sense of common or frequently occurring in the population, though it appears familiar, and is typical in the sense that it is a good example of a face that is representative of the category of faces.

Odour is sensory stimulation of the olfactory membrane of the nose by a group of molecules. Certain body odours are connected to human sexual attraction. Humans can make use of body odour subconsciously to identify whether a potential mate will pass on favourable traits to their offspring. Body odour may provide significant cues about the genetic quality, health and reproductive success of a potential mate.

<span class="mw-page-title-main">Yakovlevian torque</span> Asymmetry of the brain hemispheres

Yakovlevian torque is the tendency of the right side of the human brain to be warped slightly forward relative to the left and the left side of the human brain to be warped slightly backward relative to the right. This is responsible for certain asymmetries, such as how the lateral sulcus of the human brain is often longer and less curved on the left side of the brain relative to the right. Stated in another way, Yakovlevian torque can be defined by the existence of right-frontal and left-occipital petalias, which are protrusions of the surface of one hemisphere relative to the other. It is named for Paul Ivan Yakovlev (1894–1983), a Russian-American neuroanatomist from Harvard Medical School.

<span class="mw-page-title-main">Chirality</span> Difference in shape from a mirror image

Chirality is a property of asymmetry important in several branches of science. The word chirality is derived from the Greek χείρ (kheir), "hand", a familiar chiral object.

Personality judgment is the process by which people perceive each other's personalities through acquisition of certain information about others, or meeting others in person. The purpose of studying personality judgment is to understand past behavior exhibited by individuals and predict future behavior. Theories concerning personality judgment focus on the accuracy of personality judgments and the effects of personality judgments on various aspects of social interactions. Determining how people judge personality is important because personality judgments often influence individuals' behaviors.

Developmental homeostasis is a process in which animals develop more or less normally, despite defective genes and deficient environments. It is an organism's ability to overcome certain circumstances in order to develop normally. This can be either a physical or mental circumstance that interferes with either a physical or mental trait. Many species have a specific norm, where those who fit that norm prosper while those who don't are killed or find it difficult to thrive. It is important that the animal be able to interact with the other group members effectively. Animals must learn their species' norms early to live a normal, successful life for that species.

Mate value is derived from Charles Darwin's theory of evolution and sexual selection, as well as the social exchange theory of relationships. Mate value is defined as the sum of traits that are perceived as desirable, representing genetic quality and/or fitness, an indication of a potential mate's reproductive success. Based on mate desirability and mate preference, mate value underpins mate selection and the formation of romantic relationships.

<span class="mw-page-title-main">Axial twist theory</span> Scientific theory in vertebrate development

The axial twist theory is a scientific theory put forward to explain a range of unusual aspects of the body plan of vertebrates. It proposes that the rostral part of the head is "turned around" regarding the rest of the body. This end-part consists of the face as well as part of the brain. According to the theory, the vertebrate body has a left-handed chirality.

The ovulatory shift hypothesis holds that women experience evolutionarily adaptive changes in subconscious thoughts and behaviors related to mating during different parts of the ovulatory cycle. It suggests that what women want, in terms of men, changes throughout the menstrual cycle. Two meta-analyses published in 2014 reached opposing conclusions on whether the existing evidence was robust enough to support the prediction that women's mate preferences change across the cycle. A newer 2018 review does not show women changing the type of men they desire at different times in their fertility cycle.

References

  1. 1 2 3 Grammer, K.; Thornhill, R. (October 1994). "Human (Homo sapiens) facial attractiveness and sexual selection: the role of symmetry and averageness". Journal of Comparative Psychology. 108 (3): 233–42. doi:10.1037/0735-7036.108.3.233. PMID   7924253. S2CID   1205083 . Retrieved 4 May 2019.
  2. ↑ Rhodes, Gillian; Zebrowitz, Leslie A. (2002). Facial Attractiveness: Evolutionary, Cognitive, and Social Perspectives. Ablex. ISBN   978-1-56750-636-5.
  3. 1 2 3 Jones, B.C; Little, A.C; Penton-Voak, I.S; Tiddeman, B.P; Burt, D.M; Perrett, D.I (November 2001). "Facial symmetry and judgements of apparent health". Evolution and Human Behavior. 22 (6): 417–429. doi:10.1016/S1090-5138(01)00083-6.
  4. ↑ Penton-Voak, I. S.; Jones, B. C.; Little; Baker, S.; Tiddeman, B.; Burt, D. M.; Perrett, D. I. (2001). "Symmetry, sexual dimorphism in facial proportions and male facial attractiveness". Proceedings: Biological Sciences. 268 (1476): 1617–1623. doi:10.1098/rspb.2001.1703. PMC   1088785 . PMID   11487409.
  5. ↑ de Lussanet, M.H.E. (2019). "Opposite asymmetries of face and trunk and of kissing and hugging, as predicted by the axial twist hypothesis". PeerJ. 7: e7096. doi: 10.7717/peerj.7096 . PMC   6557252 . PMID   31211022.
  6. ↑ Kouwenhoven, Jan-Willem; Vincken, Koen L.; Bartels, Lambertus W.; Castelein, Rene M. (2006). "Analysis of preexistent vertebral rotation in the normal spine". Spine. 31 (13): 1467–1472. doi:10.1097/01.brs.0000219938.14686.b3. PMID   16741456. S2CID   2401041.
  7. 1 2 de Lussanet, Marc H.E.; Osse, Jan W.M. (2012). "An ancestral axial twist explains the contralateral forebrain and the optic chiasm in vertebrates". Animal Biology. 62 (2): 193–216. arXiv: 1003.1872 . doi:10.1163/157075611X617102. S2CID   7399128.
  8. 1 2 3 4 5 6 7 de Lussanet, M.H.E. (2019). "Opposite asymmetries of face and trunk and of kissing and hugging, as predicted by the axial twist hypothesis". PeerJ. 7: e7096. doi: 10.7717/peerj.7096 . PMC   6557252 . PMID   31211022.
  9. ↑ Britannica, The Editors of Encyclopaedia. "Ariadne summary". Encyclopedia Britannica, 24 Jul. 2021, https://www.britannica.com/summary/Ariadne-Greek-mythology. Accessed 17 October 2023.
  10. ↑ Blanz, V.; Vetter, T. (1999). "A morphable model for the synthesis of 3D faces". SIGGRAPH'99 Conference Proceedings. 7: 187–194. doi:10.1145/311535.311556. hdl: 11858/00-001M-0000-0013-E751-6 . ISBN   0-201-48560-5.
  11. ↑ Troje, N. F.; Bülthoff, H. H. (1996). "Face recognition under varying poses: The role of texture and shape". Vis. Res. 36 (12): 1761–1771. doi: 10.1016/0042-6989(95)00230-8 . PMID   8759445.
  12. 1 2 Klingenberg, C. P.; Wetherill, L.; Rogers, J.; Moore, E.; Ward, R.; Autti-Rämö, I.; Fagerlund, AA.; Jacobson, S.W.; Robinson, L.K.; Hoyme, H.E.; Mattson, S.N.; Li, T.K.; Riley, E.P.; Foroud, T. (2010). "Prenatal alcohol exposure alters the patterns of facial asymmetry". Alcohol. 44 (7): 649–657. doi:10.1016/j.alcohol.2009.10.016. PMC   2891212 . PMID   20060678.
  13. ↑ Troje, N. F.; Bülthoff, H. H. (1996). "Face recognition under varying poses: The role of texture and shape". Vis. Res. 36 (12): 1761–1771. doi: 10.1016/0042-6989(95)00230-8 . PMID   8759445. S2CID   13115909.
  14. ↑ Blanz, V.; Vetter, T. (1999). "A morphable model for the synthesis of 3D faces". Proceedings of the 26th annual conference on Computer graphics and interactive techniques - SIGGRAPH '99. pp. 187–194. doi:10.1145/311535.311556. hdl: 11858/00-001M-0000-0013-E751-6 . ISBN   0201485605. S2CID   207637109.
  15. ↑ Kowner, R. (1996). "Facial asymmetry and attractiveness judgment in developmental perspective." Journal of Experimental Psychology . Human perception and performance, 22(3), 662–75.
  16. 1 2 3 4 Perrett, D. I.; Burt, D. M.; Penton-Voak, I. S.; Lee, K. J.; Rowland; Edwards, R. (1999). "Symmetry and Human Facial Attractiveness". Evolution and Human Behavior. 20 (5): 295–307. doi:10.1016/s1090-5138(99)00014-8. S2CID   18270137.
  17. 1 2 Rhodes, G.; Proffitt, F.; Grady, J. M.; Sumich, A. (1998). "Facial symmetry and the perception of beauty". Psychonomic Bulletin & Review . 5 (4): 659–669. doi: 10.3758/bf03208842 .
  18. ↑ Britannica, The Editors of Encyclopaedia. "Ariadne summary". Encyclopedia Britannica, 24 Jul. 2021, https://www.britannica.com/summary/Ariadne-Greek-mythology. Accessed 17 October 2023.
  19. ↑ Kim, Jung-Sik; Shin, Il-Kyu; Soo-Mi, Choi (2010). "Symmetric shape deformation considering facial features and attractiveness improvement". Computer Science and Engineering. 16 (2): 29–37. doi: 10.15701/kcgs.2010.16.2.29 .
  20. ↑ Rhodes, Gillian; Sumich, Alex; Byatt, Graham (January 1999). "Are Average Facial Configurations Attractive Only Because of Their Symmetry?". Psychological Science. 10 (1): 52–58. doi:10.1111/1467-9280.00106. S2CID   53638699.
  21. ↑ Grammer, Karl; Thornhill, Randy (1994). "Human (Homo sapiens) facial attractiveness and sexual selection: The role of symmetry and averageness". Journal of Comparative Psychology. 108 (3): 233–242. doi:10.1037/0735-7036.108.3.233. PMID   7924253. S2CID   1205083.
  22. ↑ 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. CiteSeerX   10.1.1.727.1978 . doi:10.1016/j.evolhumbehav.2009.06.001.
  23. 1 2 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. doi:10.1016/j.paid.2005.02.002.
  24. ↑ Pound, N.; Penton-Voak, I. S.; Brown, W. M. (2007). "Facial symmetry is positively associated with self-reported extraversion". Personality and Individual Differences. 43 (6): 1572–1582. doi:10.1016/j.paid.2007.04.014.
  25. 1 2 Fink, B.; Neave, N.; Manning, J. T.; Grammer, K. (2006). "Facial symmetry and judgements of attractiveness, health and personality". Personality and Individual Differences. 41 (3): 491–499. doi:10.1016/j.paid.2006.01.017.
  26. ↑ Noor, F.; Evans, D. C. (2003). "The effect of facial symmetry on perceptions of personality and attractiveness". Journal of Research in Personality . 37 (4): 339–347. doi:10.1016/s0092-6566(03)00022-9.
  27. ↑ Zaidel, D. W.; Bava, S.; Reis, V. A. (2003). "Relationship between facial asymmetry and judging trustworthiness in faces". Laterality. 8 (3): 225–232. doi:10.1080/13576500244000120. PMID   15513223. S2CID   42358591.
  28. ↑ Scheib, J.E.; Gangestad, S. W.; Thornhill, R. (1999). "Facial attractiveness, symmetry and cues of good genes". Proc. Biol. Sci. 266 (1431): 1913–1917. doi:10.1098/rspb.1999.0866. PMC   1690211 . PMID   10535106.
  29. ↑ Jones, B.C.; Little, A.C.; Feinberg, D.R.; Penton-Voak, I.S.; Tiddeman, B.P.; Perrett, D.I. (2004). "The relationship between shape symmetry and perceived skin condition in male facial attractiveness". Evolution and Human Behavior. 25 (1): 24–30. doi:10.1016/s1090-5138(03)00080-1.
  30. ↑ Shackelford, T. K.; Larsen, R. J. (1997). "Facial asymmetry as an indicator of psychological, emotional, and physiological distress" (PDF). Journal of Personality and Social Psychology. 72 (2): 456–466. doi:10.1037/0022-3514.72.2.456. PMID   9107011.
  31. ↑ de Barra, Mícheál; DeBruine, Lisa M.; Jones, Benedict C.; Mahmud, Zahid Hayat; Curtis, Valerie A. (November 2013). "Illness in childhood predicts face preferences in adulthood". Evolution and Human Behavior. 34 (6): 384–389. doi:10.1016/j.evolhumbehav.2013.07.001.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.