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Imagine preparing for a job interview or a promising first date. You probably consider your outfit and general grooming—a fresh shower, plus hair products and makeup, if you use them. Glasses or contacts? Hair up or down? Various decisions signal different levels of erudition or sexual appeal, and people spend considerable time and money trying to use them to their advantage in high-stakes situations.

New research suggests, though, that elements of your appearance that are far more difficult to control also have a substantial impact on those all-important first impressions. In a recent study, researchers at the University of Texas at Dallas asked a group of American subjects to look at bodies of different shapes—not just thin and fat, but detailed variations such as pear-shaped and broad-shouldered—and assign personality traits to those shapes.

The results showed not just the range of stereotypical moral judgments people make about others’ appearances, but also how difficult it can be to change conventional wisdom—even decades after the science underpinning it has been disavowed.

The study’s 76 subjects readily assigned personality traits to body types, and they did it with considerable consistency, based only on small differences in shape. “Waist-to-hip ratio, for example, was the most important feature in women,” says Ying Hu, the study’s lead researcher. “For men, an important feature is shoulder width relative to waist size.” The subjects’ associations make clear that even small changes in body shape can still have a meaningful effect on what total strangers assume a person will be like. The fatter a body got, the more negative the traits associated with it were, like carelessness and disorganization. The leaner a body, the better a person was assumed to be, with characteristics of determination and curiosity.

The formal connection between personality and body type in academic research goes back to 1940, when the psychologist William Sheldon established the somatotypes, which are three generalized body shapes that he theorized could be linked biogenetically to personality: ectomorphs, mesomorphs, and endomorphs. Ectomorphs are people who are tall and thin, and Sheldon expected them to be shy and anxious. Mesomorphs are muscular and broad, and they’re expected to be domineering and competitive. Endomorphs are soft and round, and they’re assumed to be lazy and affection-seeking.

Since 1940, the somatotypes’ links to personality have been broadly debunked on a scientific level, with everything from Sheldon’s study methods to his assumptions about personality being called into question. And for good reason: Somatotypes were a direct result of the academic popularity of anthropometry and eugenics before World War II. According to the journalist Ron Rosenbaum, Sheldon based his research on nude photos of Ivy League and Seven Sisters college students, compulsorily photographed during their freshman year under the guise of posture correction until the practice was phased out in the 1960s and ’70s.

Sheldon didn’t interview the students, but he did use their photos to come up with the three general body shapes. He then assigned each shape personality traits based on his own observations and assumptions about personality and physical appearance. In doing so, he developed the now-discredited field known as constitutional psychology, which is the study of the link between body and behavior. Through body type, Sheldon believed it could be possible to predict things like future criminal behavior and a child’s potential for leadership—quite literally, that physique was destiny.

At the height of Sheldon’s prominence in the 1940s and ’50s, according to Rosenbaum, somatotyping was so accepted that Cosmopolitan based personality quizzes on Sheldon’s research. Eventually, spurred by outcry from the parents of the well-heeled young women he was photographing nude and by the repudiation of his techniques by a longtime research partner, schools washed their hands of him and he died in obscurity. His papers are now kept out of easy public reach at the National Anthropological Archives, and they require curator permission to view.

In these papers, Sheldon expresses explicitly racist views on how people’s appearances betray their true potential: He believed Mexican children stopped intellectually developing at age 10, for example. Although his work has attracted some lingering interest—the writer Camille Paglia discussed somatotypes prominently in her 1990 book, Sexual Personae, and they are still routinely used in some parts of the bodybuilding community—it fell out of scientific favor before his death in 1977.

Sheldon might be a mostly forgotten figure outside of academia, but the stereotypes about bodies that he codified into respected science went largely unchallenged for a generation, and many persist as cultural shorthand today. Muscular people are coded as aggressive, so much so that it affects how eyewitnesses perceive criminality when the accused perpetrator is swole. Overweight people are coded as unmotivated and underachieving, so much so that it affects employment. And despite the recent body-positivity movement, for all its media popularity, “social perceptions of fat people are not improving,” says the sociologist Deborah Carr.

One explanation for that is because of who is most likely to be overweight in America. “Obesity is very clustered in low-income populations, and in African American and Latino populations,” Carr says. These groups are already negatively stereotyped with similar traits to those presumed of fat people, like laziness, carelessness, and low intelligence, which provides an opportunity for confirmation bias. But the actual connection, according to Carr, is found in the stresses and difficulties shared among the American working class, like limited access to fresh, high-quality foods and unpredictable work schedules.

Plenty of people are willing to admit these stigmas exists, but their effects—and the effects of the long-discredited eugenics and race science that helped boost them into popular culture—are sometimes dismissed as those of hurt feelings or violated sensitivities, even though they result in measurable harm. The lingering echoes of Sheldon’s work impact not only people’s professional and romantic success, but their physical and mental well-being. Obesity is “a stressor, and any stressor that gets your cortisol levels up, whether it’s demeaning behavior or a traffic jam, can take a toll on health,” Carr says. And then “overweight people go to the doctor for something unrelated, and the first thing they hear is, ‘You gotta lose the weight,’ even if it has no direct bearing on what’s bothering them.”

There’s plenty of established science on the high stakes of first impressions and how many things go into them, but Hu told me that one of her hopes in focusing on body shapes in particular was to give people an opportunity to be more conscious of American cultural assumptions about bodies, both positive and negative. Being aware of them and their fallibility, Hu says, is the first step to being fairer. At the very least, it’s something to keep in mind the next time you shake a stranger’s hand.

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