Comparative studies of human tool making and chimpanzee feeding behaviour (which presents some challenges similar to stone tool making) have revealed distinctive forceful pinch grips used by humans that facilitate effective control of stones and minimization of injury to the fingers during tool behaviours. The second predicts that, if the first holds true, then there exist unique patterns of morphology in human hands that are consistent with these capabilities. The first hypothesis proposes that humans have unique patterns of grip and hand movement capabilities compatible with effective stone tool making and use of the tools. Studies of human hand evolution have approached these questions through a synthesis of results from tests of two hypotheses, the first focusing primarily on behaviour and performance and the second mainly on form and function.
In spite of morphological evidence from virtually all regions of the hand in several fossil species, we are still uncertain about whether (and if so how) features in the fossils might reflect specific tool-making and tool-using capabilities. habilis the tool maker? What might have been required for the hand to manipulate the tools? Should we look for evidence of hand proportions facilitating a precision grip between the thumb and index finger pad? Must there be evidence for a well-developed flexor pollicis longus muscle that could have secured a grip between the distal pads of the thumb and index finger? Did all species contemporary with stone tools make the tools? Perhaps of most concern, given the small number of fossil hand remains, might tool manipulation capabilities be inferred from just one or two ‘signals’ in the available bones? These questions persist as we review an array of hominin hand bones that has expanded substantially in recent decades. Tools have been central to interpretations of fossil hominin hand anatomy, particularly since the discovery of the Homo habilis OH 7 hand bones at the same level as stone tools at Olduvai Gorge, Tanzania in 1960. Hominin fossils are evaluated for evidence of patterns of derived human grip and stress-accommodation features.
A major remaining challenge is to identify skeletal features that reflect the full morphological pattern, and therefore may serve as clues to fossil hominin manipulative capabilities.
Comparative dissections, kinematic analyses and biomechanical studies indicate that humans do have a unique pattern of muscle architecture and joint surface form and functions consistent with the derived capabilities. Comparative analyses of human stone tool behaviours and chimpanzee feeding behaviours have revealed a distinctive set of forceful pinch grips by humans that are effective in the control of stones by one hand during manufacture and use of the tools. Was stone tool making a factor in the evolution of human hand morphology? Is it possible to find evidence in fossil hominin hands for this capability? These questions are being addressed with increasingly sophisticated studies that are testing two hypotheses (i) that humans have unique patterns of grip and hand movement capabilities compatible with effective stone tool making and use of the tools and, if this is the case, (ii) that there exist unique patterns of morphology in human hands that are consistent with these capabilities.