Individual Differences in Great Ape Cognition Across Time and Domains: Stability, Structure, and Predictability.

Understanding variation in cognitive abilities is critical to understanding both the evolution and development of cognition. In this study, we examined the stability, structure, and predictability of individual differences in cognitive abilities in great apes across a broad range of domains, including social cognition, reasoning about quantities, executive function, and inferential reasoning. We administered six tasks to 48 individuals from four species, spanning 10 sessions over 1.5 years. Task performance was most strongly predicted by stable, individual-specific characteristics rather than transient or group-level variables. Using additional data from the same individuals in other tasks, we found substantial positive correlations between nonsocial tasks. In contrast, tasks measuring social cognition were not correlated either with each other or with nonsocial measures. Future studies should work toward mechanistic models of great apes' cognitive processes to build an understanding of the evolution of cognition based on process-level commonalities across species.