Is somnambulism a distinct disorder of humans and not seen in non-human primates?

Though somnambulism (sleepwalking) is a well-recognized sleep disorder in humans, a biomedical literature search in Medline and Primate Literature bibliographic databases showed no publications on sleepwalking in non-human primates. From this finding, two inferences can be made. First is that somnambulism may be present in non-human primates; but due to limitations in expertise and methodological resources as well as narrow focus of research interest, until now researchers have not detected it in wild and/or captive conditions. Second, somnambulism does not exist in non-human primates including apes (chimpanzee, gorilla, orang-utan and gibbon); and thus, it is a unique behavioral disorder present only in humans. It is premature to conclude which of these two inferences is correct. In Jane Goodall's view, sleepwalking behavior is absent in chimpanzees. If further field observations can confirm Goodall's assertion that somnambulism is indeed absent in chimpanzees, it will be of evolutionary and medical interest to know why this parasomnic behavior became established in humans during the past 5.5 million years or so. (C) 2003 Elsevier Ltd. All rights reserved.