Michael Huffman of Kyoto University’s Primate Research Institute was watching a group of wild chimpanzees in Western Tanzania in 1987 when he saw something that first puzzled and then astonished him. His subsequent work has changed how we think about animal feeding behavior and has important implications for human medicine.
|Professor Michael Huffman holds a shoot of mjonso. In the background is Mohamedi Kalunde.|
Huffman and his colleague Mohamedi Kalunde, a game officer at the Mahale Mountains National Park, were following the chimps when they realized that one of the group, an adult female called Chausiku, was ill. She slept while the others fed on figs and ginger, and when the group moved on, she followed slowly, without feeding, frequently stopping to rest. When she came to a small tree the locals call mjonso (Vernonia amygadalina), she peeled off the bark from some shoots and chewed on the pith, swallowing the juice and spitting out the fibers.
Huffman was confounded because in 10 months of observations he’d never seen chimps eating this plant, and none of the others in the group ate it. Kalunde confirmed that it is rarely eaten by chimps, probably because of its bitter taste. Huffman then asked if the WaTongwe, the local people, have a traditional use for the plant. Kalunde told him, “Yes, it is very strong dawa (medicine).”
This was one of those moments of scientific revelation triggered by a chance observation — when ideas fall suddenly into place.
It turned out that the WaTongwe use the plant to treat upset stomachs, malarial fever and intestinal parasites. And here was a sick chimp eating it.
Chausiku made her night nest well before the usual chimp “bedtime.” The next day, about 24 hours after eating the mjonso pith, she perked up and gorged herself on all that she’d missed the day before: ginger, figs and elephant grass. This was the first documented evidence of a sick animal eating a plant with known medical properties, and recovering from the illness.
A few years later, Huffman observed another sick chimp recover after eating mjonso. The chimp’s dung contained the intestinal parasitic worm Oesophagostomum stephanostomum, but the numbers of the worms in the dung dwindled after ingesting the bitter pith. The recovery period of 20-24 hours is similar to that of sick WaTongwe who treat themselves with the plant. Self-medication in great apes has since been documented at 13 sites across Africa.
Huffman and colleagues in Japan set to work researching the human uses of Vernonia amygadalina across Africa, and trying to identify what was in the bitter juice of the plant that was curing chimps and humans.
Koichi Koshimizu and Hajime Ohigashi, plant biochemists at Kyoto, isolated from V. amygadalina 13 new steroid glucosides with antibacterial and antiparasitic properties. They have even shown that extracts of the leaves have antitumor properties. It has more than 25 medicinal uses in Africa: Its leaves are cooked (to reduce bitterness and toxicity) with meat as a tonic food, and the branches are used as “chew sticks” — the African toothbrush.
But why does this plant — like many others — have medical properties? Most plants have defense systems against animal predators. Plants produce toxic compounds that deter or reduce predation, and this has been exploited by animals for millions of years. Monarch butterflies, for instance, feed on plants that contain cardiac glucosides. Birds get sick if they eat monarchs, and learn to avoid them.
|This chimp in Tanzania is swallowing leaves whole to flush out parasitic worms.|
Chimps are similarly using plant compounds, albeit in a more sophisticated way than butterflies. Huffman has conducted noninvasive experiments to try and show how chimps acquire medical knowledge — or how they learn that certain plants make them feel better when they are ill. When Chausiku was ill and ate the bitter pith of mjonso, her son, a juvenile chimp, begged for a piece of the plant. He quickly spat it out, however, and resumed eating his ginger shoot.
Huffman says that this is how chimps learn which foods to eat and which to avoid, and in this case the young chimp might associate the bitter-tasting plant with his mother’s recovery from illness. “There are both culturally transmitted [socially learned] aspects and innately channeled behaviors,” he said. Both nature and nurture shape feeding habits.
Japanese macaques are in on the act, too. In spring they’ve been seen eating takenigusa, a bamboolike grass that contains some highly toxic alkaloids. It is used in kampo (Chinese medicine) as a poison antidote, and to treat ulcers and ear infections. (It is toxic and should not be eaten; most uses are external.) Huffman speculates that the plant is eaten to treat parasite problems.
Macaques in Arashiyama are geophages — they eat soil, up to 3 grams a day. Macaques rely heavily on high-energy, low-fiber foods, which makes them vulnerable to gastric upsets. A Tanzanian graduate student at Kyoto, James Wakibara, found that kaolin clay minerals in the soil help prevent diarrhea by buffering the gut from plant alkaloids.
Antibiotics have been overused in modern human societies to such an extent that bacterial resistance is a real health threat. With a single line of attack (antibiotics), bacteria can easily evolve resistance. Chimps have the right idea: They use mjonso plants, which contain a variety of medically active compounds, to attack gut parasites.
African nations, like China, South Korea and many other countries with a history of traditional herbal medicine, are currently integrating their age-old knowledge into a modern health-care system.
“Africa, the birthplace of humankind, may also have been the birthplace for the evolution of modern medicine,” said Huffman. What he and his colleagues are finding is that there are important lessons to learn not just from traditional medicine, but from animal medicine.