That wasn’t the first time scientists had observed what looked like self-medication in the animal kingdom. More than a decade earlier, the primatologist Richard Wrangham and his colleagues noted that chimps often swallowed whole leaves without chewing. The scientists would go on to argue that these chimps were treating parasite infections, and they eventually coined the term zoopharmacognosy — animals that know medicine — to describe the behavior. But that claim met with some skepticism. Whether those leaves actually contained chemical compounds toxic to parasites was unclear. Nor could the researchers prove that these chimps had been sick and became well after self-medicating.
Mindful of these shortcomings, Huffman began collecting fecal samples from Chausiku’s troop to get a sense of their parasite loads. Biochemist colleagues analyzed the broad-leafed plant, Vernonia amygdalina, and discovered more than a dozen new compounds with antiparasitic properties. After chimps chewed the plant, Huffman would come to learn, parasite loads (as measured by eggs in their stool) decreased by as much as 90 percent in a day. The plant was an effective dewormer. It was also known to kill domestic goats in West Africa, and that toxicity highlighted the apparent skill with which the chimps exploited the plant. Somehow they used enough to kill parasites, but not so much as to kill themselves. They also tended to chew more V. amygdalina during the wet season, when parasites were more abundant, indicating that they sought its medicinal benefits when they needed them most. They seemed to target one parasite in particular, a nasty worm called Oesophagostomum stephanostomum that could cause painful nodules along the intestinal wall and even, in severe infestations, death.
Huffman, a professor at Kyoto University in Japan, has since become a leading expert on animal self-medication. In recent decades, primatologists have shown that chimps use tools, know right from wrong and even have the ability, called theory of mind, to imagine what other chimps are experiencing. Huffman’s contribution to this increasingly nuanced understanding of our nearest relative has been to establish that, even though they lack the abilities we consider might be necessary for the development of medical knowledge — namely, humanlike language — chimps practice a form of rudimentary medicine. They know enough about the plants around them to treat illness.
Animals of all kinds, from ants and butterflies to sheep and monkeys, use medicine. Certain caterpillars will, when infected by parasitic flies, eat poisonous plants, killing or arresting the growth of the larvae within them. Some ants incorporate resin from spruce trees in their nests to fend off pathogenic microbes, employing the same antibacterial compounds, called terpenes,…