The mirror cracked: Symmetry and refinement in the Acheulean handaxe

The Acheulean is a stone tool industry that originates in Africa over 1.7 mya. It is characterised by the bifacially shaped handaxe as part of a group of tools commonly referred to as LCTs - large cutting tools. Traditionally, the Lower Palaeolithic/Early Stone Age Acheulean is seen as continuing throughout much of the Old World until c. 0.25 mya and the advent of the Middle Palaeolithic, though handaxe usage continues well after this. At least two different hominin species are responsible for making handaxes across this time span, Homo ergaster/erectus and Homo heidelbergensis. It is possible that the earliest Homo sapiens in Africa also made and used handaxes. A long running debate concerns whether or not there is an evolution in Acheulean material culture. This involves the belief that handaxes and other LCTs become more refined and sophisticated as time goes by. There are two schools of thought on this. The first argues that advances in Acheulean material culture march in lockstep with brain and cognitive evolution, whilst the second sees a mismatch between them. In this latter scenario material culture falls behind cognitive evolution. We argue that the key to understanding Acheulean material culture is variability and that symmetry and refinement in handaxes are likely to be situational/local. No long-term trends are visible in the archaeological record which show an increase in refinement or handaxe symmetry. We suggest a 'variable equilibrium' model to explain the patterns seen and show how the archaeology maps onto similar biological interpretations.