Copying error and the cultural evolution of additive vs. reductive material traditions: An experimental assessment

Copying errors that occur during the manufacture of artifactual traditions are potentially a major source of variation. It has been proposed that material items produced via ‘additive’ processes (e.g., pottery) will possess less variation than traditions produced via ‘reductive’ processes (e.g., stone knapping). The logic of this premise is that ‘additive’ production methods more readily allow for the reversal of copying errors compared to strictly ‘reductive-only’ processes. Here, we tested this hypothesis in shape data using an experimental framework in which we generated and statistically analyzed morphometric (size-adjusted) shape data under controlled and replicable conditions. Participants engaged in one of two alternative conditions: an irreversible (‘reductive-only’) manufacturing process or a reversible (‘additive-reductive’) process. With a number of factors held constant, participants were required to copy the shape of a ’target form’ as accurately as possible using a standardized block of plasticine and a steel table knife. Results demonstrated statistically greater levels of shape-copying errors in the replicas produced in the reductive-only condition. This indicates that ‘mutation rates’ in the shape attributes of artifactual traditions produced via reductive processes are inherently greater than those produced via alternative means. Several implications for the study of variation in artifactual traditions are discussed.