Sociality influences cultural complexity

Abstract

Archaeological and ethnohistorical evidence suggests a link between a population's size and structure, and the diversity or sophistication of its toolkits or technologies. Addressing these patterns, several evolutionary models predict that both the size and social interconnectedness of populations can contribute to the complexity of its cultural repertoire. Some models also predict that a sudden loss of sociality or of population will result in subsequent losses of useful skills/technologies. Here, we test these predictions with two experiments that permit learners to access either one or five models (teachers). Experiment 1 demonstrates that naive participants who could observe five models, integrate this information and generate increasingly effective skills (using an image editing tool) over 10 laboratory generations, whereas those with access to only one model show no improvement. Experiment 2, which began with a generation of trained experts, shows how learners with access to only one model lose skills (in knot-tying) more rapidly than those with access to five models. In the final generation of both experiments, all participants with access to five models demonstrate superior skills to those with access to only one model. These results support theoretical predictions linking sociality to cumulative cultural evolution.

Keywords: copying; cultural evolution; culture; evolution; social learning.

Figure 1.

(a) An illustration of the experimental design. (b) The target image for Experiment 1. Note the words ‘forty two’ at the base of the image and the red glow around these words and the circle. Participants were not required to recreate the dimension arrows. (c) The knots used in Experiment 2. Participants were asked to tie this set-up to two chairs.

Figure 2.

Mean image editing skills over 10 generations for the one-model and five-model treatments in Experiment 1. Scores rescaled between 0 and 100, where 100 is a perfect score. Linear lines of best fit emphasize a cumulative improvement in the five-model treatment and no improvement, and a possible decline, in the one-model treatment.

Figure 3.

Experiment 1 final images from participants in the one-model and five-model treatments. The target image is included at the top for comparison. The columns are chains of participants in the one-model treatment. Rows are generations going from top (generation 1) to bottom (generation 10). An obvious difference between the two treatments can be seen in the last row.

Figure 4.

Mean knot-tying skills over 10 generations for the one-model and five-model treatments in Experiment 2. Scores rescaled to between 0 and 100, where 100 is a perfect score. The loss of skills is fastest in the first three generations and much faster in the one-model treatment than in the five-model treatment. Generations 4–10 suggest different equilibria where the five-model treatment has an equilibrium at twice the skill level of the one-model equilibrium.