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Tool use, in the context of hominin evolution, is arguably one of the most important behavioral traits to define our species. As such, understanding the origins, development, and requirements of such complex behavior requires a multifaceted approach. This dissertation contributes to the growing number of studies using interdisciplinary methodologies within the context of experimental analysis to capture both the cognitive and biomechanical complexities involved in early stone tool activities. Study 1 in this dissertation demonstrates our novel and integrative protocol designed to simultaneously record electroencephalography (EEG) and surface electromyography (sEMG) during experimental stone tool tasks, collectively validating this new methodological approach and applying it to investigate how efficiency and expertise influence the neural and muscular demands of two fundamental early stone tool behaviors. Participants performed an Oldowan-style flake cutting task and a hammerstone nut-cracking task, divided into three temporally distinct stages: Hold, Aim, and Execute. Findings from the protocol closely aligned with expectations that neural activation was more pronounced in the frontal and premotor cortices during the Aim stage, regions known to be involved in action planning, decision-making, and problem-solving processes, whilst muscular activation peaked during the Execute stage, reflecting physical task performance in both the dominant and non-dominant (stabilizing) hand, validating the methodological protocol used within the experiment. A two-fold assessment was then performed in study 2 to determine participant efficiency of each task, based upon muscular activation levels and task success. Participants were categorized as Novices (lack of relevant experience), Intermediates (theoretical knowledge only), or Experts (extensive theoretical and practical knapping experience) based on their tool-related experience. Results showed that Experts performed the flake task with significantly higher success rates and lower muscular activation than less experienced participants. In the hammerstone task, no significant difference in success rates was observed between experience groups; however, Experts did show a more rapid improvement curve, suggesting a capacity for skill transfer and adaptation derived from their expansive knapping repertoire. Finally, study 3 discusses how expertise shapes neuro-biomechanical interactions during the preparatory stage (Aim) for both tool tasks. Combined analysis of EEG and sEMG data revealed clear differences between Experts and Novices. Experts engaged the left frontal and premotor/motor cortices more than Novices. This was especially true during the more cognitively demanding flake task. The increased cortical engagement was accompanied by reduced muscular activation in both hands. These findings suggest a more efficient, top-down neural control of motor output in Experts. By contrast, Novices showed increased activation in the parietal cortex, indicating greater reliance on visuospatial processing and mechanical knowledge (the ability to understand the physical properties of an object), and relatively increased activation in all muscles during both tasks. These results demonstrate task-specific neuromechanical recruitment strategies that counter the neural-efficiency hypothesis. Instead, we propose that Experts’ neural engagement may be better characterized by functional specialization and adaptive flexibility, rather than always simply reflecting a reduction in cognitive load. Together, these studies provide the first experimentally validated protocol that evidences cumulative experience leads to more efficient, targeted engagement of neural and muscular systems during early stone tool use. By segmenting tool behavior into discrete stages and adopting a combined EEG/sEMG approach, this research uncovers nuanced patterns of brain-hand interaction that would otherwise be obscured. These findings suggest that stone tool-related expertise is not merely a product of repetition but is underpinned by refined motor planning and executive functions. Furthermore, this work provides direct empirical support for the fundamental theory that the gradual expansion of the human brain likely facilitated the emergence and increasing sophistication of stone tool technologies throughout hominin evolution, either through adaptation or exaptation. This thesis thus represents a significant methodological and theoretical advancement in experimental archaeology and contributes to broader discussions within paleoanthropology about the origins of tool use and hominin evolution. |
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