People with a slender lower face are about 25 percent more likely to be left-handed, according to a researcher from the University of Washington School of Public Health and School of Dentistry. This link may also shed light on the origins of left-handedness, as slender jaws have also been associated with susceptibility to tuberculosis (TB).
[Photo: Dr. Philippe Hujoel]
“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,” said Dr. Philippe Hujoel, an adjunct professor of epidemiology at the School of Public Health and professor at the School of Dentistry. “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 study, published April 26 in the journal Laterality: Asymmetries of Body, Brain and Cognition, looked at data from 13,536 participants of three national surveys in the United States between 1963 and 1974. The surveys included information about each participant’s lower face variability and handedness.
Slender jaws are a common facial feature in the U.S. and typically affect about one in five adolescents. Past surveys measured the prevalence of slender jaws by evaluating how the upper and lower teeth come together. People with this condition typically have a lower jaw that bites a bit backward, giving them a convex facial profile and what is commonly referred to as an overbite.
The new study showed that 22 percent of children (ages 6 to 11) and 15 percent of adolescents (ages 12 to 17) had bilateral retrognathism, a dental marker for a convex facial profile and slender jaws. These same children and adolescents were also more likely to be left-handed.
“This study raises the hypothesis that the genetics, which shape facial features and TB susceptibility, also increase the likelihood for left-handedness,” Dr. Hujoel said.
Such a hypothesis may explain curious geographical coincidences, he notes. For example, the United Kingdom was described as the TB capital of Western Europe, and has a high prevalence of left-handedness and people with slender faces. Other populations, such as the Eskimos, were described as TB resistant in the 19th century, having robust facial features and typically depicted as showing right-hand dominance with tools and instruments. Whether this is more than a coincidence needs further exploration, Dr. Hujoel said.