Primate intelligence

Abstract

Brain size has traditionally been employed as a measurable proxy for species intelligence. Using allometric scaling of brain size relative to body size shows the biological cost suffered from investment in brain tissue. Shifts in diet type are the engine permitting increased investment in brain tissue because higher energy diets allow a larger brain at any given body size. Relative brain size, however, confounds effects of gut size required for particular diets wiTheffects of brain size required for enhanced cognitive function. In contrast, the absolute size of brain parts specialized for particular functions gives evidence of the computational power of those systems. Correlational analyses strongly imply that demands of social complexity, rather than difficulties associated with frugivory or embedded foods, led to evolutionary increase in simian primate brain size. Primate brain expansion has largely involved the neocortex, with correlated increases in the cerebellum; among living primates, neocortex size predicts frequency of use of tactical deception and of innovative responses. These capacities likely rely on extensive memory for social information. Only among great apes is there evidence of understanding how systems work, whether social or technical, and this ape/monkey difference may be mediated by specifically cerebellar expansion. Representational understanding may derive from the ability to parse complex behavior, allowing imitative learning of elaborate new skills.