Primate Hands

Enhanced manual grasping is considered to have been a key adaptation separating the earliest primates from other early mammals. This ability continued to evolve among primates to become most refined in humans; coevolving with bipedalism, tool-use, brain enlargement and language. Compared with other primates, the anatomy of the human hand helps to facilitate unique abilities, including forceful precision pinch grips between the pad of the thumb and the pads of the fingers and precision handling (manipulating objects within one hand). These dexterous abilities and associated anatomy are traditionally considered to have evolved in response to removing the hands from the constraints of locomotion as well as the mechanical demands of intensive tool-use and tool-production in our fossil hominin ancestors. However, there is still much debate about the inferred manipulative capabilities of early fossil hominins, particularly with regard to tool-use and potential subtle differences in precision grip movement or ability between Neanderthals and modern humans. Our work addresses this issue using proven techniques in mechanism kinematics to estimate the precision manipulation capabilities between the thumb (first ray) and index finger (second ray) across a broad sample of extant primates and fossil hominins.