An analysis of bimanual actions in natural feeding of semi-wild chimpanzees.

OBJECTIVE The objective of the current study was to investigate the lateral dominance for a bimanually coordinated natural feeding behavior in semi-wild chimpanzees. METHODS Strychnos spp. fruit consumption behaviors in semi-wild chimpanzees as an ecologically comparable feeding behavior to those found in cerebral lateralization studies of non-primate species was investigated. Video recordings of 33 chimpanzees were assessed while they consumed hard-shelled strychnos fruits. Statistical and descriptive measures of hand dominance to highlight lateralized patterns were explored. RESULTS Statistical evaluation of feeding bouts revealed a group-level right-handed bias for bimanual coordinated feeding actions, however, few individuals were statistically lateralized. Descriptive analyses revealed that the majority of individuals were lateralized and possessed a right-handed bias for strychnos feeding behavior. CONCLUSIONS The results provided empirical evidence in support of an early evolutionary delineation of function for the right and left hemispheres. The present findings suggest that great apes express an intermediate stage along the phylogenetic trajectory of human manual lateralization.