Historically, there has been a strong assumption in psychology that species can be roughly ranked by cognitive ability, based on some aspect of brain size (or the ratio of brain to body size), and that this is typically sufficient to explain differences in cognition across species. Recent research has shattered that assumption by demonstrating homologies in behavior across species with quite different brain morphology (e.g., corvids, cetaceans, and primates). However, most cases studies are still done among highly encephalized species known to do quite well in cognitive tasks. We, in collaboration with Redouan Bshary at the University of Neuchatel, are interested in how ecology shapes cognition such that even species with very small brains can outperform species with very large brains on decision-making tasks derived from the smaller-brained species’ ecology.
For this work, we are comparing primates with another highly cooperative species, cleaner fish, to elucidate the ecological pressures that have influenced cooperation. We have found that cleaner fish do indeed outperform several primates species, including humans, on tasks that are ecologically relevant to cleaner fish but not primates. This cannot be explained by basic cognition because, even on these tasks, the primates show equally fast reversal learning, indicating that the challenge was in acquiring the task in the first place. We are currently exploring the ways in which the task can be tweaked to increase the primates’ performance and, importantly, testing the fish on tasks derived from primate ecology.