Rethinking early hominin toolmaking through comparative primate models

Our understanding of human cognitive and linguistic evolution is largely dependent on inferences drawn from the experimental replication of Stone Age tools by human subjects in Western society. However, the stone-knapping behaviors of nonhuman primates may complement human models by offering additional insights into the toolmaking actions of (pre)Oldowan hominins, who in many respects were more anatomically and cognitively similar to apes than to modern humans. This study investigated whether the stone reduction behaviors of apes fall within the range of experienced modern humans. The actions of two bonobos while engaged in stone toolmaking were coded by two raters and compared to five experienced human knappers using a correspondence analysis. We found that actions associated with bonobo-made tools cluster together and are distinct from those used by modern humans to make choppers, chopping-tools, and handaxes. However, when handaxe toolmaking actions are excluded, greater overlap in action patterns emerges. The most discriminating behaviors associated with the bonobo-made tools include holding the hammerstone in their left hand and above the shoulder before striking, supporting the core on both the hand and foot or on the ground, a secant angle of percussion, and an impact location deep beyond the edge of the core. Additionally, the bonobos’ tools are associated with negative percussion results (e.g., a strike that fails to produce a flake). These results highlight the probability for equifinality in how Stone Age tools were made, calling into question our reliance on human subjects alone for inferring the evolution of technological, cognitive, and linguistic behaviors of our hominin ancestors.