Hominin reliance on Oldowan stone tools – which appear from 2.5mya and are believed to have been socially transmitted – has been hypothesised to have led to the evolution of teaching and language. Here we present an experiment investigating the efficacy of transmission of Oldowan tool-making skills along chains of adult human participants (N=184) using 5 different transmission mechanisms. Across six measures, transmission improves with teaching, and particularly with language, but not with imitation or emulation. Our results support the hypothesis that hominin reliance on stone tool-making generated selection for teaching and language and imply that (i) low-fidelity social transmission, such as imitation/emulation, may have contributed to the ~700,000 year stasis of the Oldowan technocomplex, and (ii) teaching or proto-language may have been pre-requisites for the appearance of Acheulean technology. This work supports a gradual evolution of language, with simple symbolic communication preceding behavioural modernity by hundreds of thousands of years.

It has been proposed that the uniqueness of human cumulative culture may be attributable to humans' greater orientation toward copying the process of behavior (imitation), as compared with the products (emulation), resulting in particularly high fidelity transmission. Following from previous work indicating that adult human participants can exhibit cumulative learning on the basis of product copying alone, we now investigate whether such learning involves high fidelity transmission. Eighty adult human (Homo sapiens) participants were presented with a task previously shown to elicit cumulative learning under experimental conditions, which involved building a tower from spaghetti and modeling clay. Each participant was shown two completed towers, ostensibly built by previous participants, but actually built to prespecified designs by the experimenter. This end state information was provided either in the form of photographs, or the presence of actual towers. High fidelity matching to these end states was apparent in both demonstration conditions, even for a design that was demonstrably suboptimal with regard to the goal of the task (maximizing tower height). We conclude that, although high fidelity transmission is likely to be implicated in cumulative culture, action copying is not always necessary for this to occur. Furthermore, since chimpanzees apparently copy behavioral processes and well as products, and also transmit behavior with high fidelity, the stark absence of unequivocal examples of cumulative culture in nonhumans may be attributable to factors other than imitative ability.

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Human children, in contrast to other species, are frequently cast as prolific "over-imitators". However, previous studies of "over-imitation" have overlooked many important real-world social dynamics, and may thus provide an inaccurate account of this seemingly puzzling and potentially maladaptive phenomenon. Here we investigate this topic using a cultural evolutionary approach, focusing particularly on the key adaptive learning strategy of majority-biased copying. Most "over-imitation" research has been conducted using consistent demonstrations to the observer, but we systematically varied the frequency of demonstrators that 4- to 6-year-old children observed performing a causally irrelevant action. Children who "over-imitate" inflexibly should copy the majority regardless of whether the majority solution omits or includes a causally irrelevant action. However, we found that children calibrated their tendency to acquire the majority behavior, such that copying did not extend to majorities that performed irrelevant actions. These results are consistent with a highly functional, adaptive integration of social and causal information, rather than explanations implying unselective copying or causal misunderstanding. This suggests that our species might be better characterized as broadly "optimal-" rather than "over-" imitators.