The social complexity hypothesis has been developed to explain the evolution of intelligence in mammals, particularly primates. This hypothesis proposes that intelligence evolved to deal with life in socially complex societies and predicts that species with similarly complex societies will evolve comparable levels of intelligence. I will test predictions of this hypothesis by investigating intelligence in two hyena species, the gregarious spotted hyena and the solitary stripped hyena. I will combine behavioral observations and results of playback experiments from several wild hyena clans in Kenya. Preliminary playback experiments on the study population of spotted hyenas have revealed marked sex and age differences in responses to neighboring female vocalizations. This suggests that spotted hyenas do possess some social knowledge similar to that of cercopithicine primates, and that social knowledge is sexually dimorphic and increases with age and experience. Similarities in social cognition between hyenas and primates will indicate convergent responses to the demands of social life and thus support the social complexity hypothesis. The comparative study of intelligence in spotted and striped hyenas will test the social complexity hypothesis in an alternative way by examining general intelligence in closely related species with drastically different social systems. This study will look at the evolution of intelligence