Human Evolution @ UCL


Hammerstone use during marrow extraction and flake production shown to be key variables in anatomical and functional evolution

8 April 2018

It is widely agreed that biomechanical stresses imposed by stone tool behaviours influenced the evolution of the human hand.

Handedness Sensors Though archaeological evidence suggests that early hominins participated in a variety of tool behaviours, it is unlikely that all behaviours equally influenced modern human hand anatomy. It is more probable that a behaviour's likelihood of exerting a selective pressure was a weighted function of the magnitude of stresses associated with that behaviour, the benefits received from it, and the amount of time spent performing it. Based on this premise, we focused on the first part of that equation and evaluated magnitudes of stresses associated with stone tool behaviours thought to have been commonly practiced by early hominins, to determine which placed the greatest loads on the digits. Manual pressure data were gathered from 39 human subjects using a Novel Pliance® manual pressure system while they participated in multiple Plio-Pleistocene tool behaviours: nut-cracking, marrow acquisition with a hammerstone, flake production with a hammerstone, and handaxe and flake use. Manual pressure distributions varied significantly according to behaviour, though there was a tendency for regions of the hand subject to the lowest pressures (e.g., proximal phalanges) to be affected less by behaviour type. Hammerstone use during marrow acquisition and flake production consistently placed the greatest loads on the digits collectively, on each digit and on each phalanx. Our results suggest that, based solely on the magnitudes of stresses, hammerstone use during marrow acquisition and flake production are the most likely of the assessed behaviours to have influenced the anatomical and functional evolution of the human hand.

The manual pressures of stone tool behaviors and their implications for the evolution of the human hand

Erin Marie Williams-Hatala, Kevin G. Hatala, McKenzie Gordon, Alastair Key, Margaret Kasper, Tracy L. Kivell

DOI: 10.1016/j.jhevol.2018.02.008