Chimpanzees' socially maintained food preferences indicate both conservatism and conformity

Chimpanzees remain fixed on a single strategy, even if a novel, more efficient, strategy is introduced.
Previous studies reporting such findings have incorporated paradigms in which chimpanzees learn one
behavioural method and then are shown a new one that the chimpanzees invariably do not adopt. This
study provides the first evidence that chimpanzees show such conservatism even when the new method
employs the identical required behaviour as the first, but for a different reward. Groups of chimpanzees
could choose to exchange one of two types of inedible tokens, with each token type being associated with
a different food reward: one type was rewarded with a highly preferred food (grape) and the other type
was rewarded with a less preferred food (carrot). Individuals first observed a model chimpanzee from their
social group trained to choose one of the two types of tokens. In one group, this token earned a carrot,
while in the other, control, group the token earned a grape. In both groups, chimpanzees conformed to the
trained model’s choice. This was especially striking for those gaining the pieces of carrot, the less favoured
reward. This resulted in a population-level trend of food choices, even when counter to their original,
individual, preferences. Moreover, the chimpanzees’ food preferences did not change over time, demonstrating
that these results were not due to a simple shift in preferences. We discuss social factors apparent
in the interactions and suggest that, despite seeming to be inefficient, in chimpanzees, conformity may
benefit them, possibly by assisting with the maintenance of group relations.