The evolutionary basis of human social learning

Abstract

Humans are characterized by an extreme dependence on culturally transmitted information. Such dependence requires the complex integration of social and asocial information to generate effective learning and decision making. Recent formal theory predicts that natural selection should favour adaptive learning strategies, but relevant empirical work is scarce and rarely examines multiple strategies or tasks. We tested nine hypotheses derived from theoretical models, running a series of experiments investigating factors affecting when and how humans use social information, and whether such behaviour is adaptive, across several computer-based tasks. The number of demonstrators, consensus among demonstrators, confidence of subjects, task difficulty, number of sessions, cost of asocial learning, subject performance and demonstrator performance all influenced subjects' use of social information, and did so adaptively. Our analysis provides strong support for the hypothesis that human social learning is regulated by adaptive learning rules.

Figure 1.

(a,b) A comparison of the raw data (red, average and Wilson confidence interval) and model predictions (black, median and 95% central credible interval) for (a) subject confidence and (b) the different social information conditions (where 7 : 5 means seven demonstrators make one decision while five make the other). The model closely matches the raw data, the narrower intervals for model estimates highlight the increase in precision offered by the model. (c) Median (thick lines) and 95% credible intervals (thin lines) for the probability that a subject uses social information depending on demonstrator consensus in experiments 1 and 2 (modelled as linear) and 4 (modelled as categorical). (d) The probability that subjects use social information increases with the number of demonstrators in three of four experiments, with more pronounced effects in experiments 3 and 4, which used the parallel protocol. (e) In experiments 1 and 2 the probability that a subject uses social information decreases with subject confidence in their own judgement based on asocial information (solid lines), while the probability that subject is correct increases (dashed lines). (f) The probability a subject copies a demonstrator depends on their relative performance and the absolute performance of the demonstrator. (experiment 4). Subjects respond differently to high performing demonstrators dependent on their own success, however, all subjects are equally unlikely to copy a poorly performing demonstrator.

Figure 2.

(a,b). The proportion of demonstrators that disagree with the subject's initial, asocial, choice strongly affects the probability that subjects will change their decision. (a) Decreases in subject's confidence based on asocial information (number of demonstrators = 12), and (b) increases in demonstrator number (subject confidence = low) increases the likelihood of a switch following conflicting social information. Subject behaviour, when uncertain and given many demonstrators, is conformist in that subjects are disproportionately likely to switch their decision when faced with a strong opposing majority. The black dashed lines portray the expected result of random copying. (c,d). The proportion of demonstrators reporting the shapes match strongly affects the probability that subjects' final decision will be that the shapes match. (c) In line with a conformist response to social information, when unconstrained (i.e. modelled as categorical), intermediate levels of consensus have a disproportionately large effect on decision making. The y-axis is the change to the linear predictor of the model, on which a change of magnitude four could alter the probability a subject decides the shapes match by as much as 76%. Accordingly, without other influences, social information is likely to have a dramatic effect on subject behaviour. (d) Subject behaviour, however, is also strongly affected by prior information and their confidence in it (the lines shown are for cases where subjects already believe that the shapes match). Thus, although subject behaviour may not be conformist, their response to the social information alone was conformist. The black dashed line portrays the expected result of random copying.