A preliminary survey on hand grip and hand-tool morphometrics in three different stone tools

Humans have evolved a distinctive relationship with objects (tools and technology), which has strongly influenced their anatomical and cognitive capacities. The human hand is functionally specialized for manipulation and, in terms of cognition, tools are generally integrated into the body scheme when handled. Stone tools can supply information on the evolution of this cognitive reciprocal relationship. Despite the many studies on stone tool morphology, information on hand-tool system is scanty. In this preliminary survey, we measure hand-tool distances in three lithic instruments of different size (cleaver, handaxe, convergent sidescraper), in order to investigate basic patterns associated with their handling patterns. Tool size does influence the distance from the wrist and the aperture of the hand. The associated grasping differences depend more on the tool length than on the hand morphology or dimension. Nonetheless, hand-tool metrics covariation patterns are different according to the different tool types, suggesting specific factors associated with their respective haptic experience. Females display, on average, more variability than males when handling the sidescraper, but not for the power-gripped cleaver and handaxe. We propose a new method to analyze hand-tool metrics according to the haptic interaction. These kinds of studies provide basic mandatory information which can be used to develop proper ergonomic and cognitive perspectives in tool extension and cognitive archaeology.