Read: How intelligence leads to stereotyping

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.