The origin of brain mechanisms that support human language-whether these originated de novo in humans or evolved from a neural substrate that existed in a common ancestor-remains a controversial issue. Although the answer is not provided by the fossil record, it is possible to make inferences by studying living species of nonhuman primates. Here we identified neural systems associated with perceiving species-specific vocalizations in rhesus macaques using H(2)(15)O positron emission tomography (PET). These vocalizations evoke distinct patterns of brain activity in homologs of the human perisylvian language areas. Rather than resulting from differences in elementary acoustic properties, this activity seems to reflect higher order auditory processing. Although parallel evolution within independent primate species is feasible, this finding suggests the possibility that the last common ancestor of macaques and humans, which lived 25-30 million years ago, possessed key neural mechanisms that were plausible candidates for exaptation during the evolution of language.