Rank and payoff biases influence subject choices in a foraging task among sanctuary chimpanzees (Pan troglodytes)

Social learning is essential to the development of culture in both humans and non-human primates. Transmission biases, or social learning strategies, are a key but understudied aspect of social learning. They are the cognitive processes that determine when and from whom we should learn. Primatological research has explored a handful of single biases in controlled experiments, yet few studies have considered how simultaneous strategies interact when subjects are given a dichotomous choice between two potentially adaptive biases. This study used 35 sanctuary-dwelling chimpanzees at Ngamba Island Sanctuary in Uganda to determine whether chimpanzees will copy high-ranking or low-ranking female demonstrators when those demonstrators present either a low- or high-payoff version of a token-reward task. Individuals in Group 1 observed a low-ranking demonstrator collecting the high-payoff reward (pineapple), and a high-ranking demonstrator collecting the low-payoff reward (carrot). Results concluded that chimpanzees in Group 1 did not significantly copy either demonstrator, suggesting the biases confound one another. In Group 2 the demonstrator roles were reversed, and the frequency of high-payoff selection was higher. Therefore, whilst humans may be able to overlook demonstrator characteristics to ratchet culture in beneficial ways, chimpanzees might not be able to do the same. This contributes to explanations as to why chimpanzee culture is simple compared to that of humans.