Experimental evidence for the co-evolution of hominin tool-making teaching and language

Abstract

Hominin reliance on Oldowan stone tools-which appear from 2.5 mya and are believed to have been socially transmitted-has been hypothesized 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 five 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.

Figure 1

Experimental design and structure. (a) A diagram of the stone knapping process. The hammerstone strikes the core with the goal of producing a flake. The platform edge and angle are important to the success of knapping. (b-f) The five learning conditions. (g) The structure of the experiment. For each condition 6 chains were carried out (4 short and 2 long); one of two trained experimenters started each chain (equally within each condition).

Figure 2

Performance across conditions and along chains. Values shown are the median model estimates and the corresponding 95% central credible intervals. More complex forms of communication, in particular verbal teaching, increased several measures of participant performance, including (a) the total quality of all flakes, (b) the number of viable flakes, (c) the proportion of flakes that were viable, (d) the rate at which viable flakes were made, (e) the proportion of the core knapped and (f) the probability that each hit resulted in a viable flake. The brackets marked with double asterisks indicate contrasts for which there is strong evidence of a difference (95% credible interval excluding 0), single asterisks indicate cases for which there is weak evidence of a difference (90% credible interval excluding 0). The red bracket in panel (c) indicates that the increase in performance from imitation/emulation to basic teaching is greater than the increase between all other adjacent conditions. (g,h) Although verbal and gestural teaching increased the probability of a viable flake per hit and the proportion of flakes that were viable, performance in these conditions decreased along chains such that across conditions performance was similar by position 5. With reverse engineering, performance did not decline along chains, suggesting it was already at floor levels. Position 1 corresponds to the first participant, not the trained experimenter. (i) With verbal teaching, both the total number of utterances (left hand bars) and the probability a teaching utterance was correct (right hand bars) decreased along chains. Key: reverse engineering-blue (n=37), imitation/emulation-green (n=34), basic teaching-yellow (n=38), gestural teaching-orange (n=37), verbal teaching-red (n=38).