Animal Heal Thyself

Apes and other creatures regularly dip into nature's medicine chest; do their natural remedies hold promise for people?

• Michael Lipske
• Dec 01, 1993

You think you've seen everything and then the nice, middle-aged man in a coat and tie leans forward in his seat at the coffee shop and pretends to eat a leaf from the fake philodendron at the center of your table. His eyes gleam as if he has discovered a delectable morsel, his lips encircle the leaf tip and then he pauses to inquire, "You ever see them?"

His name is Eloy Rodriguez, a University of California-Irvine phytochemist, and he is demonstrating how wild chimpanzees consume the leaf of the African herb Aspilia. "They'll do it one at a time," he explains. "They'll never chew it." That's because the chimps aren't exactly feeding; what they seem to be doing is taking their medicine. "They come up to about right here, and then they'll cut it off," says Rodriguez, grabbing a fake leaf between thumb and forefinger and pretending to eat it.

A bit of a showman, Rodriguez seems unconcerned about raising a few eyebrows in a coffee shop. Who can blame him? He and a handful of other scientists are exploring a new field of study that is increasing our understanding of animal behavior as well as holding out hope of new drugs to battle human diseases, including cancer.

Zoopharmacognosy is the new field's mouthful of a name. Coined in 1987 by Rodriguez and colleague Richard Wrangham, a Harvard University anthropologist, the term refers to animal use of medicinal plants to treat illness. Like headache-afflicted humans rummaging through medicine cabinets, several species of animals are now known to seek out (if often instinctively) plants that have various medicinal properties.

Some monkeys in Brazil eat a fruit that may function as a fertility drug. Bears in North America chew up and then smear in their fur a root that may repel fleas and other pests. Birds of several species do "anting," the rubbing of live ants on their feathers, presumably relying on the insects' defensive secretions as natural fungicides or insecticides. And observations in the African jungle, along with lab work by scientists like Rodriguez, suggest that chimpanzees seek out plants that act as treatments for intestinal parasites. "We think there is some learning and that knowledge is passed on-and that this has been going on for a long time," Rodriguez says of the apparently self-medicating chimps.

"Wild apes five or six million years ago were already using plants [as medicine]," maintains Rodriguez. "And as the human line evolved, we obviously learned from animals. We observed them. It gives us a peek into how we came about selecting medicinal plants." Already, more than a fourth of modern prescription drugs are derived from rainforest plants, either directly or by plant ingredients serving as templates for creation of synthetic compounds. And scientists say that so far only about 1 percent of tropical-forest plant life has been studied for its medical potential.

The problem is separating the pharmacological wheat from the chaff. "There's no way we can screen every plant out there," says Kenneth Glander, a Duke University primatologist looking at possible medicinal plant use by howler monkeys in Costa Rica. "So why not let the primates do the screening?"

Anthropologist Wrangham was one of the first researchers to take note of unusual feeding behavior among wild chimpanzees. Chimps usually consume leafy food with all the delicacy of young humans attacking bowls of popcorn. But as early as the 1970s, Wrangham found chimps in Tanzania's Gombe National Park feeding on Aspilia in a far more studied manner. In one paper he wrote that the animals would "sometimes close their lips over a leaf, remain still for a few seconds, then abandon the leaf without detaching it from its stem." And when a chimp did find a suitable leaf, the animal would roll it around in its mouth for a few seconds and then swallow it whole, sometimes with a grimace. Wrangham tried eating a few Aspilia leaves himself, "but I never actually managed to get them down."

Large and covered with bristly hairs, the leaves are hardly appetizing, he says. "I'm not surprised the chimpanzees make a kind of a `gulp' as it goes down." He learned more after sending some leaves to Rodriguez, an expert on Aspilia's sunflower family. Rodriguez's research team extracted from the leaves a bright red oil known as thiarubrine-A. When tested, it turned out to be strong stuff, able in low doses to kill a variety of worms, fungi and viruses. With in vitro tests at Purdue University, low concentrations of thiarubrine-A have killed cancer cells of the sort found in solid tumors of the colon and lung.

"That seemed very exciting," says Rodriguez. "One of the first drugs that we discovered in studying the apes turned out to be a very good antitumor and antiviral drug." Thiarubrine-A still must be tested on animals and humans before it proves its worth. But long before scientists began studying the substance or the plant, African villagers were routinely using extracts of Aspilia to treat infections and other ailments.

Nor is Aspilia the only plant-derived drug consumed by both chimps and humans. Vernonia (commonly called bitter leaf) kills internal parasites and is widely used as a medicine by people throughout Africa. People with intestinal complaints tend to feel better about 20 hours after consuming the plant's juice. So, it seems, do chimps. Working in Tanzania, primatologist Michael Huffman of Kyoto University in Japan, has on several occasions seen lethargic, diarrhea-afflicted chimpanzees split open sterns of Vernonia shrubs, suck the bitter-tasting juice from the pith and then seem to feel better roughly 20 hours later.

In 1991, he had stool samples from one such chimp analyzed. "We found her parasite level had dropped quite dramatically," he says. "The compounds in the pith she ingested had some kind of effect on the intestinal flora."

To Huffman, such behavior is very likely intentionally aimed at ridding the body of sickness. He is now investigating more than a dozen other wild plants he suspects are chimpanzee medicines. Each plant is also used medicinally by people living in the same areas as the chimps.

In Uganda, chimpanzees swallow leaves of Rubia cordifolia, a plant deemed so dandy for easing stomach ailments that local villagers cultivate it in home gardens. Ugandan chimps also carefully select and chew young leaves of a particular species of fig tree. Tests by phytochemist Rodriguez reveal that the fig leaves contain 5- methoxypsoralen, an antibiotic compound that kills nematodes, or wormlike parasites. He jokes, "Instead of covering themselves with fig leaves, Adam and Eve probably should have taken it as medicine; it would have been a smarter thing to do."

Chimpanzees are not the only creatures rummaging in nature's chemical cabinet. Before reusing an old nest, starlings line it with fresh green vegetation that tends to contain volatile chemicals which may discourage external parasites. Capuchin monkeys in Costa Rica rub their fur ("perfuming themselves," Rodriguez calls it) with a dark-colored mix of trunk ooze and rainwater that collects in pools at the base of certain trees. Rodriguez suspects that certain compounds in the solution "might act as a natural 'OFF' or `6-12'," protecting the monkeys against biting insects.

Some animals may use plants to control reproduction. During mating season, woolly spider monkeys in the Brazilian rain forest eat fruit from a tree known locally as monkey ear. The fruit contains stigmasterol, a chemical from which the hormone progesterone has been synthesized and which anthropologist Karen Strier of the University of Wisconsin suspects could stimulate female muriqui fertility.

Costa Rica's howler monkeys may also eat plants to influence reproduction. In two decades of fieldwork, Duke University scientist Kenneth Glander has learned that female howlers often bear offspring of only one sex, usually males. Genetically, such a strategy enables a mother monkey to pass more of her genes on to future generations through male offspring. Statistically, however, such patterns are anything but probable. Glander suspects that certain plants eaten by howlers may influence the gender of their offspring, perhaps by altering the chemistry of the vagina to be more hospitable to sperm carrying a Y-chromosome.

Elephants may induce labor with diet. Holly Dublin, the World Wildlife Fund's regional scientific officer for eastern Africa, tracked a pregnant elephant for a year in the mid-1970s. The elephant routinely followed the same feeding schedule, moving only about 5 miles a day. "Then all of a sudden she made this very long move, as I recall about 28 to 30 miles," says Dublin. The animal stopped at a small tree-not one Dublin had seen the elephant eating before--and ate it down to the stump before returning to her usual territory. A few nights later, the elephant gave birth. Dublin later learned that the plant is one Kenyan women use to induce labor.

Then there is the enthusiastic response of bears to Ligusticum porteri, a carrot-family member also known as bear root. Several years ago at a zoo in Colorado Springs, Colorado, ethnobotanist Shawn Sigstedt offered samples of the plant to Kodiak brown bears. "To everyone's astonishment," he recalls, the animals chewed up the root, created a paste of it and rubbed it on their faces. Using tongue action, they also sprayed the pomade over their bodies.

Ligusticum contains coumarins (the same chemicals that provide the pleas- ing smell in new-mown hay) that may offer bears relief from fleas, ticks and even fungus conditions.. The plant may also contain a chemical similar to one bears naturally generate as an attractant. The scientist says bears appear to grow calmer after a session with the root, and animals long antagonistic to one another have been seen rubbing noses.

To anthropologist Richard Wrangham, though, there is a big difference between the way bears respond to Ligusticum and the medical practices of chimpanzees he is studying in Africa. He points out that bears seem always to respond to Ligusticum, not just when they appear ill. "It seems to me it could be something like when cats respond to catnip," he says. And fur-perfuming capuchins "are doing something very similar to what birds do when they `ant'," he adds. "But we don't know whether they have any illness when they do this." The capuchin behavior may be an instinctive response to chemicals in their environment.

On the other hand, Wrangham says, chimpanzees-perhaps the most intelligent terrestrial animal besides man-now provide convincing cases of obviously sick animals seeking and ingesting a known medicinal plant, and then showing improved health. But, asks Michael Huffman, "How much of what they're doing are they really aware of?"

Either way, the results so far are captivating to researchers. "We're just at the tip of it," says phytochemist Rodriguez. "It's not every day you open up a new field. We kind of popped it open and now a whole bunch of questions are being generated." For example, does rising zoopharmacognostical awareness add to the moral obligation to protect jungle habitat? "Look at the animals," says Rodriguez. "Can you imagine what happens when you start removing some of their medicines from the rain forest?"

Zoopharmacognosy's findings also provide a powerful (and selfish) reason for humans to stop destroying tropical forests and creatures that live in them. How will we understand the usefulness of nature's pharmacy if we can't watch, as our ancestors likely did, what the rest of the neighborhood is swallowing?

Washington, D.C., writer Michael Lipske has written for National Wildlife about whale status in American waters, U.S. forest policy and catfish farming.