The study of self-medication in non-human primates sheds new light on the complex interactions of animal, plant and parasite. A variety of non-nutritional plant secondary compounds and nutrient-poor bark is found in the primate diet, but little is yet known about the possible medicinal consequences of their ingestion. Recent studies of the African great apes support a hypothesis in progress that the non-nutritional ingestion of certain plant species aid in the control of parasite infection and provide relief from related gastrointestinal upsets. Detailed behavioral, pharmacological and parasitological investigations of two such behaviors, bitter pith chewing and leaf swallowing, have been conducted on three East African chimpanzee populations, but they are now known to occur widely among all chimpanzee subspecies, as well as bonobos and lowland gorillas. For both bitter pith chewing and leaf swallowing, selection of the same plant species tends to occur among neighboring groups of same ape species. These local cultural traditions of plant selection may be transmitted when females of the same species transfer into non-natal groups. However, selection of the same plant species or species of related plant genera by two sympatric ape species or between regional populations of great ape subspecies strongly suggests a common criteria of medicinal plant selection. This and the intriguing observation that the same medicinal plant is selected by apes and humans with similar illnesses provide insight into the evolution of medicinal behavior in modern humans and the possible nature of self-medication in early hominids. The occurrence of these and other specific self-medicative behaviors, such as fur rubbing and geophagy, in primates and other animal taxa suggest the existence of an underlying mechanism for the recognition and use of plants and soils with common medicinal or functional properties.

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ObjectivesGeophagy, the intentional consumption of earth, is widely practiced among humans and other mammals, but its causes are not well understood. Given the growing number of reports of geophagy among nonhuman primates (NHP), we sought to (1) advance and codify our understanding of the patterns and functional and evolutionary significance of geophagy among NHP and (2) provide a research agenda for a more unified approach to its study.MethodsWe systematically reviewed all available literature on NHP geophagy, extracted available data on taxa, geography, climate, diet, sex, age‐class, reproductive status, and the characteristics of the earth. We used these data to evaluate three major hypotheses about geophagy, that it is protective, provides mineral supplementation, and is nonadaptive.ResultsWe identified 287 accounts of geophagy among 136 species, adding 79 new primate species to the list of those considered in prior reviews. Nineteen percent of species were in the suborder Strepsirrhini, while 81% were in the suborder Haplorrhini. There were reports of geophagy from 9 of the 17 families and 39 of the 76 genera currently recognized by the International Union for Conservation of Nature.DiscussionThe limited evidence suggests that geophagy is adaptive, and provides protection and mineral supplementation. We specify the behavioral, dietary, and soil data required to more rigorously investigate these hypotheses across representative species of all taxonomic groups, geographical regions, and dietary classification. Given the plausibility of geophagy for maintaining the health of both wild and captive populations, we urge further study and conservation of geophagy sites.

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We examined bone mineral density (BMD) of the femoral neck and lumbar vertebrae of four chimpanzee skeletons from Mahale Mountains National Park, Tanzania, and four captive ones, with a dual energy X-ray absorptiometer. The BMD of Wansombo, an old female chimpanzee from Mahale, was remarkably lower than the mean of the other six younger adult female chimpanzees and categorized as osteoporosis. Posture, locomotion, and trunk-sacral anatomy of chimpanzees may have prevented fractures in Wansombo, whose BMD was below human osteoporosis criteria.