Abstract
This study tests the hypothesis that aspects of human mental illness also occur in chimpanzees. Because humans and chimpanzees are so close evolutionarily, with regards to genes and sociality, it was hypothesized that these species might also share a common range of illnesses. This study focused on behavioral indicators of profound social withdrawal because it is an easily observable and unambiguous sign of mental illness in humans. To test the research hypothesis, a five question retrospective survey was completed by caretakers and directors of zoos and sanctuaries. The survey asked respondents to provide behavioral reports of profound social isolation within four contexts, if it was exhibited by any of their chimpanzees. Responses were received for a total of 51 chimpanzees. Two of these chimpanzees were identified as exhibiting profound social isolation that was considered homologous to voluntary social isolation exhibited by humans afflicted with mental illness. The implications of these results, as well as the limitations and suggestions for future research are discussed.