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
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