Is there geographical variation in human handedness?

Abstract

Right- and left-handed individuals are present in all cultures. However, while it is known that handedness is a heritable trait, little is known about how handedness varies between populations-and without this knowledge, the significance of the left/right polymorphism is hard to interpret. We reviewed the literature to assess the extent of geographical variation of throwing or hammering handedness. These two tasks were chosen because they are present in all known cultures (unlike, for example, writing), and make sense within the context of several adaptive theories on the origin of laterality, or maintenance of handedness polymorphism, which state that tool or weapon manipulation are pivotal. A total of 81 samples were found with primary data on throwing or hammering handedness, spanning 14 countries and concerning more than 1,214,000 individuals studied between 1922 and 1998. A global logistic regression was performed to assess the significance of the country of the study, controlling for several potentially confounding variables (date of the study, sex and age of individuals). Country always had a significant effect, consistent with substantial geographical variation of throwing and hammering handedness. Curiously, left-handedness frequency estimates for a given country were not always consistent across datasets, perhaps due to missing variables, such as educational level or socio-economic status. Results are discussed in the context of the evolution of handedness and the significance of the current polymorphism.