Hadza handedness: Lateralized behaviors in a contemporary hunter–gatherer population

Abstract

Handedness has been studied extensively in Western populations and in non-human primates. Seldom, however, has this focus been extended to non-industrialized populations. This study examines handedness from an evolutionary perspective in an ecologically meaningful setting. The sampled population, the Hadza of Tanzania, are a contemporary hunter–gatherer people whose handedness behaviors represent an important, and yet neglected, avenue of investigation. Ethological sampling methods were utilized based on recorded video footage of an ethnographic nature. This footage was coded and analyzed to document dominant hand use in a range of evolutionarily relevant activities, such as hunting and foraging tasks. Strength of lateralization was compared across task categories. The results demonstrate that the Hadza are extremely lateralized in tool-use tasks, with 96% of all tool-use tasks being executed with the right hand. Importantly, strength of lateralization was not influenced by degree of tool complexity. They were less strongly lateralized for more commonplace, empty-handed tasks (such as eating or communicative gestures). They were the least lateralized in object manipulation tasks. These results support theoretical scenarios which place tool use at the centre in the evolution of human right-handedness.