Although intelligence should theoretically evolve to help animals solve specific types of problems posed by the environment, it is unclear which environmental challenges favor enhanced cognition, or how general intelligence evolves from domain-specific cognition. The social intelligence hypothesis posits that big brains & great intelligence have evolved to cope with the labile behavior of group-mates. Here we exploit the remarkable convergence in social complexity between cercopithecine primates and spotted hyenas to test predictions of the social intelligence hypothesis in regard to both cognition and brain size. Behavioral data indicate that there has been considerable convergence between primates and hyenas with respect to their social cognitive abilities. Moreover, compared to other hyena species, spotted hyenas have larger brains and expanded frontal cortex, as predicted by the social intelligence hypothesis. However it appears unlikely that domain-general intelligence can evolve exclusively in response to selection pressures imposed specifically in the social domain.