The role of raw material differences in stone tool shape variation: an experimental assessment

Abstract

Lithic raw material differences are widely assumed to be a major determining factor of differences in stone tool morphology seen across archaeological sites, but the security of this assumption remains largely untested. Two different sets of raw material properties are thought to influence artifact form. The first set is internal, and related to mechanical flaking properties. The second set is external, namely the form (size, shape, presence of cortex) of the initial nodule or blank from which flakes are struck. We conducted a replication experiment designed to determine whether handaxe morphology was influenced by raw materials of demonstrably different internal and external properties: flint, basalt, and obsidian. The knapper was instructed to copy a “target” model handaxe, produced by a different knapper, 35 times in each toolstone type (n = 105 handaxes). On each experimental handaxe, 29 size-adjusted (scale-free) morphometric variables were recorded to capture the overall shape of each handaxe in order to compare them statistically to the model. Both Principal Components Analysis (PCA) and a Multivariate Analysis of Variance (MANOVA) were used to determine if raw material properties were a primary determinate of patterns of overall shape differences across the toolstone groups. The PCA results demonstrated that variation in all three toolstones was distributed evenly around the model target form. The MANOVA of all 29 size-adjusted variables, using two different tests, showed no statistically significant differences in overall shape patterns between the three groups of raw material. In sum, our results show that assuming the primacy of raw material differences as the predominant explanatory factor in stone tool morphology, or variation between assemblages, is unwarranted.