Handedness in gestural and manipulative actions in male hunter-gatherer Aka pygmies from Central African Republic

摘要

Objectives: All human populations display a right-biased handedness. Nonetheless, if studies on western populations are plenty, investigations of traditional populations living at subsistence levels are rare. Yet, understanding the geographical variation of phenotypes of handedness is crucial for testing evolutionary hypotheses. We aimed to provide a preliminary investigation of factors affecting handedness in 25 Aka pygmies from Central African Republic when spontaneously gesturing or manipulating food/tools (N_(actions)=593). Materials and methods: We recorded spontaneous behaviors and characterized individuals' hand preference using GLMM with descriptive variables as target position, task complexity (unimanual/ bimanual), task nature (food/tool manipulation, gesture), and task physical/cognitive constraints (precision or power for manipulative actions and informative content for gestures). Results: Individuals were lateralized to the right (93%, N=15) when manipulating food/tools but not when gesturing. Hand preference was affected by target position but not by task complexity. While nonexplicitly informative gestures were more biased to the right compared to explicitly informative ones, no differences were found within food/tool manipulation (power or precision vs. none). Discussion: Although we do not intend to assume generalizable results due to our reduced sample, our observations provide additional information on handedness in a contemporary traditional society. Especially, the study mainly evidenced considerable cultural effects in gestures while also supporting theories considering active tool manipulation as one of the overriding factor in human handedness evolution.