Exploring the evolutionary roots of theory of mind: Primate errors on false belief tasks reveal representational limits.

Human adults flexibly reason about others' unobservable mental states, a capacity known as Theory of Mind (ToM). Unfortunately, the roots of this capacity still remain poorly understood as both infants and nonhuman primates perform inconsistently on tests of ToM. Here, we try to better understand this complex and often contradictory literature by dissecting nonhuman primates' failures on false belief tasks. Across four studies (n = 566 subjects), we find that-despite succeeding on a closely matched control-rhesus monkeys fail to predict how agents with false beliefs will behave even when those agents perform unexpected actions. We interpret this pattern of performance as evidence that monkeys fail to maintain a representation of another agent's recent knowledge once the environment changes outside of that agent's awareness thus preventing monkeys from making any predictions about the agent's future actions. Overall, this work helps to move beyond the success/failure dichotomy typically used to assess ToM performance, and instead provides a more precise characterization of primates' signature limits in ToM, which we speculate may also be shared with human infants.