An Investigation of the Use of Medicinal Plants by Wild Chimpanzees

It has been proposed that chimpanzees use a number of toxic plant species for their medicinal value. Based on behavior, plant pharmacology, and ethnomedical information, hypotheses concerning the medicinal use of some of these plants by chimpanzees include the following: control of parasites, treatment of gastrointestinal disorders, regulation of fertility, and possible anti-bacterial or anti-hepatotoxic activity. With regards to bitter pith chewing and whole leaf swallowing behaviors, 20 medicinal plant species have been observed to be used not only by chimpanzees, but also by bonobos and lowland gorillas at 7 sites (Mahale, Gombe, Kibale, Kahuzi-Biega, Wamba, Tai, Bossou) across Africa. A detailed description is given of the research program currently being carried out by the author and colleagues of the international research team, The C. H. I. M. P. P. Group, and in particular, of the ongoing multi-disciplinary research into the chimpanzee use of Vernonia amygdalina (Del.) in the Mahale Mountains National Park Tanzania. The hypothesis that this species has medicinal value for chimpanzees comes from detailed observations by the author of ailing individuals' use of the plant. Quantitative analysis and assays of the biological activity of V. amygdalina have revealed the presence of two major classes of bioactive compounds. The most abundant of these constituents, the sesquiterpene lactone vernodalin, and the steroid glucoside vernoioside B1 (and its aglycones) have been demonstrated to possess antibiotic, anti-tumor, anti-amoebic, anti-malarial, anti-leishmanial, and anti-schistosomal properties. At Mahale, the particular parts of an additional 12 plant species ingested by chimpanzees are recognized for their traditional use against parasite or gastrointestinal related diseases in humans. Their physiological activities are now being investigated in the laboratory.