Cultural accumulation or stasis? The impact of imitation and early teaching on hominin cultural evolution

One way to investigate the origins of cumulative culture is by examining the increasing complexity of lithic technologies in the hominin lineage. This study presents a simplified model of cultural transmission in Homo erectus and Homo heidelbergensis, focusing on the emergence of cumulative culture in relation to Oldowan, Acheulean, and the transition to Mode 3 technologies. Acheulean toolmaking likely required high-fidelity transmission, possibly supported by early forms of teaching. However, the remarkable technological conservatism of the Acheulean record contrasts with the rapid accumulation of innovations in modern humans. Our model aims to shed light on this circumstance by analysing the roles played by imitation and early forms of teaching. Each lithic technology is classified into three behavioural levels (0-2), representing increasing complexity and adaptive value, which can be acquired through individual learning or social transmission. We introduce two genotypes: the Imitator, which enables basic social learning, and the Assessor, which adds evaluative teaching between parents and offspring. We analyse the cultural dynamics generated by each genotype in pure populations. Our results suggest that incremental cumulative culture depends critically on offspring reliably replicating the most complex behaviours of their parents. This dynamic favours the evolution of the Assessor genotype, as it enhances parent-offspring behavioural resemblance. Nonetheless, when replication fidelity falls short of establishing the highest level of complexity behaviours (Level 2) predominant, the Assessor genotype may inadvertently reinforce cultural stasis instead of driving cumulative cultural evolution, ultimately hindering the transition from Level 1 to Level 2 behaviours via individual learning.