for National Geographic News
Clay soils consumed by both chimps and humans in Uganda's Kibale National Park contain high concentrations of the mineral kaolinite, a main ingredient in some anti-diarrheal medications.
Experts had previously suggested that chimps ate the fine-grained clay to help ward off intestinal ailments or to obtain added minerals in their diet.
But a French team recently observed that the chimps eat dirt before or after consuming leaves from the Trichilia rubescens plant, which contains potent medicinal chemicals.
Eating the bitter vegetation alone gives the chimps no health benefit, researchers say.
Instead the plant's malaria medicine is activated when fine soil particles bind with chemicals in the leaves.
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Chimps often select dirt that has been exposed on the roots of newly fallen trees, added study co-author Sabrina Krief, of the Muséum National d'Histoire Naturelle in Paris.
"This may be to avoid worms, bacteria, and stones," she said.
Krief and colleagues described the research online in the January issue of the journal Naturwissenschaften.
In humans, soil consumption—or geophagy—has often been viewed as a sign of metabolic disorder or even mental illness.
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