The use of medicinal drugs is often viewed as a uniquely human exercise. In Doctors by Nature, however, Jaap de Roode shows that many non-human animals also practice medicine. Building on his own research on monarch butterflies, and taking us on a tour around the globe, de Roode introduces us to a whole menagerie of medicating animals, from apes to ants, from bees to baboons, and from cats to caterpillars. Studying how animals use medicine is not only fascinating, but also useful. By learning how animals use drugs, we can improve the livestock industry, save pollinators, and even find new drugs to treat human diseases.
What is Doctors by Nature about?
JdR: The book tells a story of how animals use drugs to prevent or treat infectious diseases, how scientists study animal medication, and what we can learn from animals. Many of us have long thought that medicine is a uniquely human thing; that we are the only species clever enough to develop drug treatments to treat all sorts of ailments. But it turns out this is completely wrong! Back in the 1980’s, scientists turned started describing how chimpanzees use toxic chemicals from plants and rough “velcro-like” leaves to expel parasitic worms from their guts. And while chimpanzees are our closest living relatives, we now know that many animals use medicine, including insects.
Can you give some examples of animals that use drugs?
JdR: Of course! Goats and sheep like to eat plants with tannins to kill intestinal parasitic worms. Woolly bear caterpillars eat alkaloids to kill parasitic flies. My own research has shown that monarch butterflies can use toxic milkweed chemicals as medicine. Monarch caterpillars are specialized on feeding on milkweeds, but milkweed species vary in their concentrations of these toxins. When infected female monarchs lay eggs on milkweed, they unintentionally transfer some of their parasites to those eggs. But by laying their eggs on more toxic milkweed, they ensure that their offspring caterpillars are less likely to become infected, and that they will suffer less disease. A fine example of “mother knows best”.
So, is all animal medicine based on swallowing drugs?
JdR: No. Cats coat themselves with mosquito repellents when rolling around on catnip, and orangutans mix their saliva with the chemicals from medicinal lianas to treat skin wounds. Starlings add aromatic plants to their nests that protect their chicks against mites. And ants and bees add resin, the sticky stuff that trees produce, to their colonies, which fights off viruses, bacteria and fungal pathogens.
How do animals know what to do?
JdR: Many cases of animal medication probably depend on innate mechanisms. When woolly bear caterpillars are infected with parasitoid flies, their taste receptors that detect alkaloids start firing at higher rates, making the caterpillars eat more of the chemicals. But animals can also learn from their experiences. Sheep and goats are really good at making associations between foods they eat and relief from worm infections. So, the next time they are infected, they specifically eat medicinal plants. Animals can also learn from each other. When chimpanzees swallow whole leaves to expel worms, they first fold them before putting them in their mouths. Chimpanzees can use different ways to fold the leaves, and in each social group, they copy how to from each other.
What was most surprising to you when writing this book?
JdR: Although scientists have only studied animal medication for a few decades, traditional healers and shamans have known that animals use medicine for thousands of years. In fact, healers have developed many treatments for humans by copying the behaviors of animals. Take Native Americans: many of the tribes in North America have at least one treatment that is referred to as “bear medicine”, because healers discovered them by observing bears. Oshá root is a well-known medicinal herb, but it looks like even aspirin was first discovered by bears. Following their hibernation, bears tend to eat the bark of willow trees to reduce inflammation. Scientists later extracted salicylic acid from willows and changed it chemically to make the super drug.
Are there other examples of drugs that were first discovered by animals?
JdR: Oh, yeah. In Tanzania, healers credit elephants, chimpanzees and porcupines with the discovery of drugs to treat stomach upset, intestinal worms, and bloody diarrhea. Ethiopian goats, dancing around after eating coffee berries, taught us about the stimulatory effects of caffeine. In South America, people first learned about the stamina-increasing properties of cocaine by looking at Peruvian llamas. Maybe you have heard about horny goat weed? This weed is used for erectile dysfunction, and a Chinese goat herder discovered it when he noticed that his goats got frisky when eating it.
What inspired you to write the book?
JdR: I have always wanted to write a book, and I was so happy to be able to write about this topic. I want people to recognize just how clever animals are, and how amazing nature is. I have always had a love for animals, and recognizing that animals have all these fantastic ways of treating themselves and each other is just fascinating. But I also want readers to realize that the study of animal medication is not restricted to a few select scientists, but that it really is for everyone. I describe how an American primatology professor worked with a traditional healer in Tanzania to discover chimpanzee medication. But I also show how undergraduate students in Mexico and Japan discovered that birds use cigarette butts to clear their nests of blood-sucking parasites, and that cats love catnip because it prevents mosquito bites; and how volunteer researchers in the Democratic Republic of Congo are studying primates to discover new anti-malarial drugs.
What would you like for people to take away from the book?
JdR: Hopefully, the book will show just how much we can gain from studying animal medication. By giving animals the opportunity to be their own doctors, we can improve the welfare of our livestock and pets, reduce the overuse of antibiotics, and save honey bees from dying. I also hope to give people yet another reason to protect and restore nature. By realizing that the world’s ecosystems are a goldmine of yet to be discovered drugs, we will hopefully add a little more urgency to preserving nature.
About the Author
Jaap de Roode is Samuel Candler Dobbs Professor of Biology at Emory University, where he studies monarch butterflies, teaches biology, and trains graduate students in infectious disease biology. He is also on the board of directors of the Rosalynn Carter Butterfly Trail, with the aim to recreate pollinator habitat.