Individuals who have slender lower faces are 25 percent more likely to be left-handed, according to a study published this week by a dentistry researcher from the University of Washington. The surprising finding came from three surveys comprising 13,536 people in the United States.
People having slender jaws commonly have a lower jaw that bites backward somewhat, lending them a convex facial profile, referred to as an overbite. Slender jaws are a common facial feature, affecting about one in five U.S. adolescents.
Study author Philippe Hujoel, a professor at the University of Washington School of Dentistry, said:
“Almost 2,000 years ago a Greek physician was first to identify slender jaws as a marker for TB susceptibility, and he turned out to be right! Twentieth-century studies confirmed his clinical observations, as slender facial features became recognized as one aspect of a slender physique of a TB-susceptible person. The low body weight of this slender physique is still today recognized by the Centers for Disease Control and Prevention as a marker for TB susceptibility.”
Tuberculosis, Lefties And Overbite
Courtesy of Philippe Hujoel
The finding suggests the hypothesis that genetics which shape facial features and tuberculosis susceptibility also increase the likelihood for left-handedness. The theory could also potentially explain certain geographical coincidences.
For example, the United Kingdom was described as the tuberculosis capital of Western Europe, and has a high prevalence of left-handedness and people with slender faces. Other populations, such as the Eskimos, were in the 19th century described as tuberculosis-resistant, having robust facial features, and typically depicted in art as showing right-hand dominance with tools and instruments.
Of course, all this could just be a weird coincidence, so the idea needs further exploration, Hujoel said.
In the early 20th century, slender individuals were described as “ectomorphs” — a term that persists in popular culture as a reference to dieting and bodybuilding, Hujoel noted.
“In a world dominated by an obesity crisis and right-handers, ectomorphs can be different in their desires,” he said. “Popular websites suggest they commonly express a desire to gain weight or muscle mass. Their slightly increased chance of being a ‘leftie’ is an additional feature that makes them different.”
Philippe P. Hujoel
Handedness and lower face variability: Findings in three national surveys
Laterality: Asymmetries of Body, Brain and Cognition, 2017; 1 DOI: 10.1080/1357650X.2017.1317265