Physiognomy is the ancient art and now science of deducing someones personality and character from their appearance, especially from the features of the face, possibly including expression and movement patterns across a brief amount of time.
Physiognomy has gotten out of fashion in mainstream scientific research due to its pseudoscientific history. Physiognomy is commonly compared to forms of quackery such as phrenology (the belief that one could determine a person's personality and propensity to engage in criminal activity by evaluating the bumps on their head). With the machine learning hype, the field has regained some recognition, e.g., machine learning was used to detect people's individual's behavioral tendencies via facial analysis; however, it remains unclear whether the software can produce above-chance results based on facial or contextual cues.
There have also been many scientific studies linking physical appearance with certain personality/character traits above chance, though most researchers shy away from using the term 'physiognomy' explicitly.
More tangible results are described below, but none of them have effect sizes large enough that one could assume them to be consistently accurate in actual lived experience. However, proponents of modern physiognomy argue that making decisions based on even a small correlation is superior to doing so based on no information. The chances of making a correct prediction increase as certain traits tend to stack on top of each other.
Regardless of the validity of physiognomic judgments in general, people frequently make very severe and swift judgments based on stereotypes and perceived physiognomic characteristics. As there appear to be genuine associations between appearance and actual behavior (however weak these associations are), the natural human tendency to 'judge a book by its cover' likely has adaptive value. This tendency helped ancestral man avoid potentially dangerous situations (or choose particularly suitable sexual partners or allies) in his evolutionary past. These cognitive heuristics based on superficial appearance would likely have lead to higher reproductive success for those that acted on them for long enough that this judgmental tendency was bred into the human gene-pool over time.
In recent years, many studies have concluded that facial features are correlated with perceived and actual personality and character traits. The following is a quick summary of some of these findings:
- A meta-analysis of 19 studies found a weak but statistically significant correlation between fWHR (a measure of the broadness of the face) and aggression, ranging from r = .09 for field and archival studies to r = .21 for studies conducted in research labs. Another study in 2016 found weak but significant correlations between various psychopathic traits and fWHR, (r = .12 for the whole sample and r = .27 for a sample of prison inmates). This is possibly mediated by an association between fWHR and higher levels of pubertal testosterone exposure.  A study in 2017 found that fWHR possibly influences social status; with Popes and CEOs typically having higher than average fWHRs. This is possibly due to such leaders being more effective and socially dominant, or due to them being perceived to be so.
- A twin study in 2017 found a weak but significant relationship between wider IPD (Interpupillary distance) and actual measured IQ. An earlier study found that people were able to accurately gauge measured IQ from a photograph, but this only held true in the case of men's IQ, and not women's.
- Studies conducted in 2013 found that people were able to accurately predict the outcomes of fights based on facial features, above chance. The fighters with faces rated as more aggressive were more likely to win their bouts, but they was also confounded by weight, thus it only held true for heavyweight fighters. The facial features associated with aggressiveness were an overall broader face, broader chin, darker eyebrows and horizontally narrowed eyes.
- Wang & Kosinski (2017) used a deep neural network that, analyzing 35,326 'selfie' images, correctly determined homosexuality in 81% of cases for men, and in 74% of cases for women. This was compared to human judges, who could distinguish a man's homosexuality in 61% of cases and women's in 54% of cases (slightly above chance). This study has been heavily criticized, however, for being confounded by differences in facial expression, grooming, clothing, camera angle and other contextual factors unrelated to facial structure.
- Holtzman (2011) created a series of prototypical faces corresponding to each of the traits of the dark triad, using the photos of 81 study participants, who completed self-report inventories designed to measure the levels of the dark triad traits. The participants were also evaluated in regards to their level of dark triad traits by their peers. It was found that observers could (above chance) correctly distinguish between high and low morphs of the various "dark traits", thus lending some evidence to the idea that these traits are correlated with a certain facial structure. This correlation was explained by several hypothesis, the facial traits and the dark triad being co-evolved, the facial traits influencing people's self perception and thus behavior, or that individuals are possibly conditioned to behave in a way 'congruent' with their facial structure by peers, through constant social reinforcement.
Modern physiognomy research
- A Chinese study examined the association between fWHR and domestic violence in 144 individuals of both sexes (Wen & Zheng, 2020) found a medium effect size (d = .67) for greater fWHR (as measured to the midbrow) and the men's likelihood of being involved in a domestic violence incident in the past. No such association was found for the female subjects, though greater fWHR was associated with certain aspects of interpersonal dominance. The effect size was much more substantial for fWHR as measured to the midbrow compared to measuring it to the eyelid. However, both were statistically significant and fairly large compared to the usual effects one finds in the social sciences. This discrepancy in effect sizes for the two alternative forms of measuring of fWHR may suggest the midbrow measurement is more accurate in terms of discerning the effects this particular facial metric has on behavior. This discrepancy in the predictive validity for various measures of fWHR is something to keep in mind when interpreting the results of such research. 
- Skorska et al. (2015) used a computer modeling program that examined the facial metrics of N = 390 male and female subjects of varying sexual orientations. It was found that lesbians had 'marginally more masculine facial shapes,' upturned noses, puckered mouths, and smaller foreheads than heterosexual women. Homosexual men tended to have more sloped foreheads, convex cheeks, and smaller noses (with nose size being typically considered a masculine feature, perhaps due to larger noses generally indicating greater prenatal androgen exposure, when controlling for ethnicity)  compared to heterosexual men. Therefore, the researchers concluded that facial structure was associated with sexuality in both men and women. This is likely due to prenatal hormonal exposure playing an important role in determining later sexual preferences, while also partially determining facial bone development.
- Wang & Kosinski (2017) used a deep neural network that, analyzing 35,326 'selfie' images, correctly determined homosexuality in 81% of cases for men, and in 74% of cases for women. The decisions made by the neural network were compared to human judges, who could distinguish a man's homosexuality in 61% of cases and women in 54% of cases (slightly above chance). However, this study has been heavily criticized for being confounded by differences in facial expression, grooming, clothing, camera angle, and other contextual factors unrelated to facial structure.
- A twin study in 2017 found a weak but significant relationship between wider IPD (Interpupillary distance) and actual measured IQ. An earlier study found that people were able to gauge measured IQ accurately from a photograph, but this only held in the case of men's IQ, not women's.
Mental health physiognomy
- Certain behavioral conditions may result in particular facial expressions. For example, very intense people might bite their lips, crunch their teeth, chew their nails and engage in other nervous tics. Autists are often described to have an empty, monotonous facial expression. Some mental conditions result in a tilted mouth. Socially excluded individuals may develop tics as nobody is there to correct their behavior, or such behavior may be induced by the greater stress such people often face. People are, in fact, able to infer other's mental conditions above chance level based on photos. Autists are often recognized as less approachable and attractive within seconds.
- Foo et al. (2019) found that women relied on men's attractiveness, facial masculinity, and overall perceived trustworthiness to attempt to determine their likelihood of committing infidelity, however of these traits only facial masculinity predicted actual infidelity related behaviors above chance. This effect however, was weak, with only 14.1–18.0% of raters being able to accurately gauge men's infidelity related behaviors above chance. There was no such effect found for women, despite men being able to judge infidelity related behaviors above chance in other men. Earlier research, found that men could only make above accuracy judgements of infidelity when presented with two women, one of whom had committed infidelity several times in the past compared to who had not.
- A study in 2017 found that fWHR influences social status, with Popes and CEOs typically having higher than average fWHRs. This association between fWHR and social dominance is due to either broad-faced leaders being more effective and socially dominant, or due to their being perceived to be so.
Eyes • Lateral orbital rim • Lips • Lower third • Mandible • Maxilla • Eyebrow • Feet • Browridge • Moustache • Breasts • Buttocks • Feet • Browridge • Vagina (also known as pussy) • Penis • Testicles
Macrophallism • Midface ratio • Neoteny • Sexual attractiveness • Sexual dimorphism Facial Aesthetics: Concepts and Clinical Diagnosis • Fashion • Anteface • Fivehead • Frame • FWHR • Compact midface • Deep-set eyes • Hunter eyes
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