Are you a leftie? Chances are you also have a slender face and an overbite

28 April 2017 - 13:15 By TMG Digital
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Image: Gallo Images/iStock

People with a slender lower face are about 25% more likely to be left-handed.

The unexpected finding was identified in 13 536 individuals who took part in three surveys conducted in the United States.

The association may shed new light on the origins of left-handedness‚ because slender jaws have also been associated with susceptibility to tuberculosis‚ a disease which affects two billion people.

About one in five adolescents in the US have slender jaws‚ and they typically also have a lower jaw‚ which bites slightly backwards‚ giving them a convex facial profile and an overbite.

"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 Philippe Hujoel‚ who wrote about the link to left-handedness in the journal Laterality: Asymmetries of Body‚ Brain and Cognition.

"Twentieth-century studies confirmed his clinical observations‚ as slender facial features became recognised as one aspect of a slender physique of a TB-susceptible person. The low body weight of this slender physique is still today recognised by the Centers for Disease Control and Prevention as a marker for TB susceptibility‚" added Hujoel‚ a professor at the University of Washington School of Dentistry.

He said the finding raises the hypothesis that genetics‚ which shape facial features and tuberculosis susceptibility‚ also increase the likelihood for left-handedness.

Such a hypothesis may explain curious 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.

Whether this is more than a coincidence 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."

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