The evolution of combinatoriality and compositionality in hominid tool use: a comparative perspective

Abstract

A crucial design feature of language useful for determining when grammatical language evolved in the human lineage is our ability to combine meaningless units to form a new unit with meaning (combinatoriality) and to further combine these meaningful units into a larger unit with a novel meaning (compositionality). There is overlap between neural bases that underlie hierarchical cognitive functions required for compositionality in both linguistic and nonlinguistic contexts (e.g., tool use). Therefore, evidence of compositional tool use in the archaeological record should signify, at the very least, the cognitive capacity for grammatical language by that point in time. We devise a novel system to evaluate the level of hierarchical nesting of tool components in single tool use activities. In the application of this system, we demonstrate that nonhuman primates, and by extension, the last common ancestor shared by Pan and Homo, are capable of basic combinatoriality; however, their technology does not approach the compositionality observable in modern human tool use. The prehistoric archaeological record supports a continuous evolution of combinatorial tool use into compositional tool use, with evidence for human-like levels of by 0.93 million years ago (Ma), or possibly as early as 1.7 Ma. While compositional language could have lagged behind compositional tool use, if language and technology coevolved according to the Technological Origin for Language hypothesis, which proposes a feedback system between the two, then evidence for hierarchical tool use structures implies a similar level of complexity in linguistic structures.