The when and who of social learning and conformist transmission

Formal evolutionary models predict when individuals rely on social learning over individual learning and the relative strength of their conformist social learning biases. Here we use both treatment effects and individual variation to test predictions about the impact of (1) the number of traits in an environment, (2) the adaptive or payoff relevance of those traits, (3) the fidelity of transmission, and (4) the size of groups. We find that both social learning and the strength of conformist transmission increase with the number of traits, the adaptive value of those traits, and the fidelity of transmission. The strength of conformist transmission increases with group size, but only when there were 2 traits in the environment. Using individual-level variation and recognizing that treatment effects predictably impact individuals differently, we show that IQ negatively predicts social learning, but has a U-shaped relationship to conformist transmission, suggesting strategic use of conformist-biased social learning among those with the highest IQ. Other plausible predictors, such as status, cultural background, and personality, were not predictive. Broadly, our results reveal that not only is the conformist transmission bias ubiquitous, but that past experiments, both human and non-human, have likely underestimated its prevalence and the prevalence of social learning by restricting designs to only 2 traits.