Technology, expertise and social cognition in human evolution.

Paleolithic stone tools provide concrete evidence of major developments in human behavioural and cognitive evolution. Of particular interest are evolving cognitive mechanisms implied by the cultural transmission of increasingly complex prehistoric technologies, hypothetically including motor resonance, causal reasoning and mentalizing. To test the relevance of these mechanisms to specific Paleolithic technologies, we conducted a functional magnetic resonance imaging study of Naïve, Trained and Expert subjects observing two toolmaking methods of differing complexity and antiquity: the simple 'Oldowan' method documented by the earliest tools 2.5 million years ago; and the more complex 'Acheulean' method used to produce refined tools 0.5 million years ago. Subjects observed 20-s video clips of an expert demonstrator, followed by behavioural tasks designed to maintain attention. Results show that observational understanding of Acheulean toolmaking involves increased demands for the recognition of abstract technological intentions. Across subject groups, Acheulean compared with Oldowan toolmaking was associated with activation of left anterior intraparietal and inferior frontal sulci, indicating the relevance of resonance mechanisms. Between groups, Naïve subjects relied on bottom-up kinematic simulation in the premotor cortex to reconstruct unfamiliar intentions, and Experts employed a combination of familiarity-based sensorimotor matching in the posterior parietal cortex and top-down mentalizing involving the medial prefrontal cortex. While no specific differences between toolmaking technologies were found for Trained subjects, both produced frontal activation relative to Control, suggesting focused engagement with toolmaking stimuli. These findings support motor resonance hypotheses for the evolutionary origins of human social cognition and cumulative culture, directly linking these hypotheses with archaeologically observable behaviours in prehistory.