Walter Lewis


Ethnobotanist: World expert on airborne and allergenic pollen and famous for targeting medicinal plants in the tropical rain forest.

"Do what you enjoy and go where your heart takes you."

Ethnobotany is the study of plants by obtaining information from people around the world. The Lewises specialize in discovering new drugs extracted from plants used in folk medicine by native tribes in South America and other tropical parts of the world.

Three-quarters of all modern drugs come directly or indirectly from plants used in folk medicine. The Lewises are desperately trying to catalogue the wide variety of plants used by tropical rainforest cultures before the forests are chopped down. They have collected thousands of plants and found dozens of traditional medicines. These include a wound-healing tree sap that helps cuts and scrapes heal 30 percent faster. Other plants treat malaria, hepatitis, diarrhea and more. In 2003 Walter Lewis and his colleagues at Washington University in St. Louis submitted an anti-malarial patent based on their collaborative research with Peruvian natives, who also own part of the patent. Meanwhile, Memory Elvin-Lewis collaborated with Peruvian physicians and U.S. researchers on studies demonstrating the value of traditional hepatitis remedies.

The tropical jungles where most of these plants grow are disappearing. At the same time, the people who know how to use these plants are becoming more “Westernized” (steeped in the culture of North America and Western Europe) and are losing their traditional culture and knowledge of the forest. The Lewises are trying to talk with these people before it is too late. The plants they discover may become widely used miracle drugs of the future.

Achuar ethnobotany. Click to enlarge.

1. The hut: The Achuar hut sits in a clearing in the forest. It’s about 12 metres long and seven metres wide. Several families live together inside. Unmarried and widowed women live at one end. Meetings are held at the other end around a Snake Stool, where the headman or apu sits. Open fires burn on the floor and the smoke goes out a hole in the roof.

2. An Achuar elder: Now dead, this wise elder taught the Lewises much about the medicinal plants of the Achuar.

3. Gourd with holly leaves: Each morning, before dawn, the Achuar men drink guayus, a very strong, pleasant-tasting caffeine drink made from holly leaves. Each man usually drinks about a litre; within 45 minutes he vomits about half of it back up. The vomiting is not caused by the guayus but is a custom of the tribe. When boys reach maturity, they join the men in the morning ritual of drinking and regurgitating guayus. It is considered an honour, and boys look forward for years to this right of passage. The Lewises do not know why the tribe has developed this custom. Perhaps vomiting every morning is a healthy ritual in a jungle environment where many deadly parasites thrive.

4. Methylergonovine: When Walter Lewis returns from the jungle to his university laboratory, he uses chemical identification techniques to determine the molecular structure of the active ingredients in the medicinal plants he brings back. This is a typical diagram of a molecule similar to the active ingredient in the ergot-like fungus the Lewises found growing on a plant used by Achuar women to aid in childbirth.

By observing and talking to native people from India, Africa and the Americas, the Lewises have learned how some trees cause allergies. They have been called upon to advise cities in their tree-planting policies. The Lewises have also studied the use of chewing sticks by hundreds of millions of native people around the world instead of toothbrushes. One example is the bark of the neem tree, which, when chewed, provides anti-microbial and anti-inflammatory effects that can reduce gingivitis (gum disease). However, the couple report that neem bark also contains chemicals that could cause cancer. Memory Elvin-Lewis, commenting on the safety of natural herbal remedies in her 2001 landmark review of herbal medicines in the Journal of Ethnopharmacology, says, “The notion that ‘natural is safe’ has little meaning in reality unless, of course, one puts into the same context the idea that ‘pharmaceutically derived’ is not always totally beneficial.” The Lewises like to point out that naturally occurring medicines can be very beneficial, but they must be treated with the same caution and respect as conventional medicines from commercial drug companies.

The Lewises have achieved their goal as ethnobotanists by cataloguing the medicinal plants of the world in an 800-page book, Medical Botany: Plants Affecting Human Health. While they started by observing and recording how indigenous cultures used medicinal plants, eventually their research shifted: they began working with chemists and pharmacologists to develop new medicines from the plants they discovered. “Things have changed,” says Walter Lewis. “Everyone is concerned with intellectual property when you collect a plant. If you use native know-how, you have to pay them upfront for the privilege of collecting specimens even during the development phase.”

The Lewises now spend the greatest percentage of their time negotiating among native peoples, the university and pharmaceutical companies. They want to get marvellous new drugs to cure diseases such as hepatitis, tuberculosis and malaria, but they also want the native people to be adequately compensated and to retain part ownership of patents and the medicinal knowledge of the plants their tribes have used for centuries. “We invent the chemistry and pharmacology to say precisely what is going on with a medicinal plant,” says Dr. Lewis, “but the native people own the knowledge of the medicinal qualities of their plant.” But large drug companies wish to benefit commercially from these new medicines, too. It’s a delicate balance and takes a lot of time.

Twenty years ago, Western ethnobotanists like the Lewises could find a remote rainforest tribe, learn its herbal remedies and simply take whatever plant material they wanted back to their laboratories for study. Today, things are different. The potential commercial value of drugs derived from jungle herbal medicines is in the hundreds of billions of dollars. Realizing this, indigenous peoples have formed organizations to protect their wealth of plant knowledge. The Lewises now must arrange their explorations with a Peruvian group called the Confederación de Nacionalidades Amazónicas del Perú (CONAP), which represents 18 Amazonian tribes. They have to negotiate payment for doing research, and they must agree to share any wealth arising from discoveries. The Lewises also want to help protect the tribal knowledge, so they now encode data and keep plant names secret to ensure nobody steals that knowledge.

There are other ethical dilemmas in the rainforest. “If you discover that one tribe has found a cure for some disease, can you ethically tell a neighbouring tribe which plant it is?” asks Dr. Lewis. He will not give out this information, but he will name a contact person in the other tribe.


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In the Peruvian jungle, the Achuar have shown the Lewises a plant they use to treat “the frightened people.” The Lewises do not know what the Achuar mean by this, but they feel that if this mystery could be solved, a new drug for anxiety or some forms of mental illness might be discovered.

Explore Further

Memory Elvin-Lewis, “Should We Be Concerned about Herbal Remedies?” Journal of Ethnopharmacology, no. 75, 2001.

Walter Lewis and Memory Elvin-Lewis, Medical Botany: Plants Affecting Human Health, John Wiley & Sons, 2003.

Walter Lewis, et al., “Ritualistic Use of the Holly Ilex Guayusa by Amazonian Jivaro Indians,” Journal of Ethnopharmacology, no. 33, 1991.

An introduction to ethnobotoany on the U.S. National Health Museum website.

Read Walter Lewis's answers to questions...The StoryCareer Advice