Biomimicry

by Janine M Benyus

  Also discussed at the meeting was the whole realm of medicines applied in non-oral fashion. Anecdotes abound about birds such as eagles that line their nests with resin-soaked pine sprigs, perhaps to keep out nest parasites. The blue jays on your front lawn may also be practicing a form of medicine. In a ceremony called anting, jays squeeze ants in their beaks and then rub the formic acid onto their feathers. They seem to have an almost beatific look on their faces as they do this, as if the ant juice is intoxicating. Other investigators have postulated that anting is actually an antiparasitic gesture—a delousing.

  Bears are also known to exhibit strange rubbing behavior. After spending seven years with a Navajo family and learning about traditional tribal medicines, Harvard ethnobotanist Shawn Sigstedt became intrigued by the fact that there were so many medicinal plants with names that included “bear.” Traditional Navajo teachings said that medicines were given to people by the bears, a good indicator that the Navajo might have watched animals self-medicating and then adopted their practices. Sigstedt put the bear connection to the test with Ligusticum porteri, a vanilla-celery-scented herb that grows in the Rocky Mountain and Southwest regions of the United States and is used by the Navajo to treat worms, stomachaches, and bacterial infections. He gave samples of the plant to polar bears and grizzly bears in the Colorado Springs Zoo, and watched in amazement as they rolled and rubbed with relish, perhaps getting relief from ticks or skin fungi.

  How Did Animals Learn to Self-medicate?

  In a way it seems contradictory. How could the practice of eating toxins to self-medicate have evolved, when there is so much evolutionary pressure not to eat toxins? As with safe eating, says Richard Wrangham, there are probably physiological, behavioral, and cultural aspects to the phenomenon of curative eating.

  First the physiological. Depending on what an animal needs in its diet, even hardwired tastes can reverse themselves. When an animal wakes up sick, for instance, it might find its aversion to secondary compounds transformed into a tolerance or even a craving for bitter leaves. Chinese herbalists have used this body feedback for thousands of years when treating human patients. As Michael Huffman reported at the AAAS conference, “Sick people supposedly tolerate a level of bitterness utterly repellent to healthy individuals, allowing the herbalists to identify when and how to adjust their doses.” The sicker a patient is, the more bitterness he’ll tolerate. When he starts complaining that the medicine is too bitter, the herbalist pronounces him cured.

  Jane Goodall has experimental evidence that seems to support this theory. When Goodall needed to treat some chimpanzees with tetracycline, a bitter substance, she hid it in bananas, and watched who ate what. While the healthy chimps turned up their noses at the laced treats, the sick chimps quickly ate the bananas, seemingly oblivious to the bitterness. In wild feeding, Huffman found that chimpanzees with the highest parasite loads tend to eat the bitterest leaves. Glander observed a similar flip-flop in howlers’ tastes. Healthy howlers avoid leaves that are high in tannins and therefore hard to digest. On days when they are sick, however, the same animals lose their caution and go after high-tannin leaves, perhaps because the tannins bind to and escort plant poisons out of their system. Red colobus monkeys (Procolobus badius) are shown to do the same out-of-the-ordinary selecting when nursing a stomachache.

  What looks like a momentary flight from good judgment may actually be a trip to the tropical medicine chest, say the zoophar-macognosists. Of course, as is true of so much of animal behavior theory, no one can prove this—at this point it’s a matter of conjecture and common sense. “Most other primatologists have been reluctant to accept this self-medication explanation,” writes Glander in one of his papers, “but they have been unable to offer other cogent explanations for the occasional ingestion of tannin-rich plant material by primates such as red colobus and howlers.”

  In addition to physiological motivators, conditioning behaviors may also play a role in self-medication. The ultimate enforcer of bitter-leaf-eating behavior is to have a bitter leaf soothe an ailment. It’s the flip side of the so-called Sauce Béarnaise syndrome, which causes an animal to associate negative body sensations with a particular food. Just as the scientist who named the syndrome is unlikely to order Béarnaise again, good experiences with a given food could have the opposite effect, acting to encourage that particular eating behavior.

  Cultural learning may also help to shape the habit of self-medication. Bennett G. Galef, Jr., and Matthew Beck, psychologists at McMaster University in Ontario, observed that rats are more likely to try a cure for their ailments if they are surrounded by other rats that already prefer the food. Even if they’ve been conditioned to be phobic about it, they may give it a try if everyone else is doing it. We primates are especially good at mimicking behavior, which turns out to be a survival skill. The fellow who got sick on bad Béarnaise might have been spared if he had been able to watch his tablemate double over after eating the stuff. Similarly, if a chimp stumbled onto a good thing with the Vernonia pith, others would quickly see the wisdom in it.

  As with smart eating, modeling Mom’s behavior is probably the first way primates learn about medicinal plants. After they’re grown, they watch and imitate how their troopmates handle illness. This sampling of good medicines may be another reinforcement for socialization. Says Kenneth Glander, “I think this is a social phenomenon to the extent that the group can contain much more knowledge than a single individual can, particularly when that knowledge is in a three-dimensional space—different leaves within the same tree have different properties and the material has to be handled in a different fashion when you are medicating.”

  While it’s easy to conjecture how sickness might prompt an animal to treat itself, how do you explain the fact that perfectly healthy animals sometimes leave their troops and travel for miles to select certain plants at certain times of year? If the animals are not sick, what are they responding to? Sometimes the answer is easy. In the case of moose, a springtime gorging on aquatic plants is a quest for salt, which is largely absent from its winter diet. But what about animals that are not starved for nutrients, and yet spend their energy traveling to a particular plant at a particular time of year? Could they be preparing their body for something? Curious, anthropologist Karen Strier decided to accompany the muriqui monkeys of Brazil on one of their seasonal “food runs.”

  Plant Parenthood: It’s Not Just for Stomachaches Anymore

  To keep up with these beautiful monkeys, Karen Strier, author of Faces in the Forest, has to run pell-mell through Brazil’s Atlantic Forest. Overhead, her subjects are like trapeze artists, swinging from branch to branch at breakneck speed. The males and the females grow to an identical size, the cap set by the need to be lightweight enough for branch-top travel. This equal stature helps make muriqui (Brachyteles arachnoides) one of the most peaceful and egalitarian species of primates ever studied. They are also, unfortunately, one of the world’s rarest primate species. Habitat destruction has already claimed 95 percent of their home in the unique Atlantic Forest, and fewer than one thousand of the beautiful muriquis are left in a handful of isolated populations.

  Keeping track of them in the remains of their jungle can be exhausting. Thankfully for Strier and her students, the monkeys take frequent breaks for feasting, mostly on fruit. When their mating season dawns, however, the muriquis suddenly switch horses. They ignore the fruits and set their sights almost exclusively on the leaves of two tree species in the legume family, Apuleia leiocarpa and Platypodium elegans. Upon analysis, Strier found that the leaves of both species are notably low in tannins, a substance known to interfere with protein digestion. Like Popeye squeezing open a can of spinach just before a fight, the monkeys may be looking for a surge of protein before mating, and therefore go for the more digestible, low-tannin leaves. The leaves may also contain compounds that prevent bacterial infections, which could help bolster the monkeys’ health when they need it most.

  Strier also notice
d that besides eating different leaves, muriquis tend to take road trips during this time of year. They speed from the center of the jungle to the edge of their ranges, where the forest thins out into clearings. Here, they eat the fruit of a third species of legume, called Enterolobium contortisiliquum, or monkey ear. The fruit is full of stigmasterol, a phytoestrogen that we humans use to synthesize progesterone. Could it be, asks Strier, that the muriquis eat monkey ear in preparation for, or perhaps to influence the timing of, mating season? Is there such a thing as “reproductive eating”?

  Kenneth Glander is asking the same question about mantled howler monkeys. He became suspicious when he recorded a number of highly gender-skewed births in howlers. Some females in the group were having broods consisting of nine out of ten males or four out of five females. This swamping of sexes cannot be understood by statistical averages.

  Could it be, thought Glander, that the howler monkeys are eating something that might improve the odds of having either male or female offspring? Are they somehow changing the electrical environment of the vagina (by eating either acidic or alkaloid foods) and thereby either blocking or rolling out the red carpet for a particular sperm type? The idea is not so outlandish when you consider that a sperm carrying an X chromosome (female-producing) is electropositive, while a sperm carrying a Y chromosome (male-producing) is electronegative. Since like repels like, a negative environment in the vagina might block negatively charged sperm while assisting positively charged sperm. Glander tested his hypothesis by measuring the electric potential at the entrance to howlers’ vaginas and at the cervix. There was enough of a difference in the millivolt readings between the two locations to convince him that, depending on what they ate, howlers might be able to “produce an electrical charge and change it from positive to negative.”

  If plants could be used to stack the gender deck, the plant-as-medicine theme expands to include plant-as-population-shaper. But why the manipulation? Glander explains: If the population is short on males, a female that produces males has a good chance of producing one that will be a troop leader. Producing a son who is a leader confers status on the mother (better access to food and safety, for instance). If the population is low on females, however, the mother may want to have females who will likely become first lady—making the mother an in-law of royalty. “All of us are familiar with the phrase ‘You are what you eat,’ ” Glander says. “But I suggest that we may be what our mother eats.”

  Strier and Glander were not the first to postulate this phenomenon in mammals. In 1981, Patricia Berger found that plant compounds seem to influence reproduction in voles. If primates and even voles can influence when and if they will be fertile in response to environmental conditions, could it be that animals are in finer harmony with their environment than we have given them credit for?

  At this point, we know of ten thousand secondary compounds, but chances are that animals, insects, birds, and lizards know of and have been experimenting with lots more. They may use them to prevent illness, to cure illness, maybe even to influence their fertility, abort their fetuses, or influence the gender of their offspring—all in response to environmental opportunities and limits of the moment. Compared to these real natives, we’ve been snooping around the jungle pharmacy for only a brief moment, long enough to know there’s much, much more.

  NOT MUCH TIME ON THE CLOCK

  There was a time, not so very long ago, when we relied exclusively on plants, microbes, and animals for new drugs, and that’s where we found 40 percent of all our prescription medicines. Here’s a small sampling of what plants alone have given us in the field of pharmaceuticals:

  Taxol, isolated from the bark of the Pacific yew tree (Taxus brevifolia) in the Pacific Northwest, is a promising new drug used to treat ovarian and breast cancer patients.

  The steroid hormone diosgenin, isolated from wild yams (Dioscorea composita) in Mexico, was an essential ingredient in the first contraceptive pills.

  Vincristine and vinblastine, isolated from the Madagascar periwinkle (Catharanthus roseus), are used to treat Hodgkin’s disease and certain kinds of childhood leukemia.

  A semi-synthetic derivative of the May apple (Podophyllum peltatum), a common woodland plant in the eastern United States, is used to treat testicular cancer and small-cell lung cancer.

  Digitalis, from the dried leaves of the purple foxglove (Digitalis purpurea), is used to treat congestive heart failure and other cardiac disorders.

  Reserpine, isolated from the roots of tropical shrubs in the genus Rauwolfia, is used as a sedative and to treat high blood pressure.

  By the close of the 1970s, however, plants fell out of favor as candidates for pharmacological research. Soil bacteria and fungi kept yielding new antibiotics, and synthetic chemistry and molecular biology—under the rubric of “rational drug design”—were seen to be the next great source of drugs. We decided we didn’t need plants to create our cures.

  Today, conditions have conspired to bring plant sampling back in vogue. After a few decades of sifting through the soil in their own backyards, pharmaceutical companies are beginning to turn up the same old microbes, but no new drugs. Scientists are also finding it harder than they thought to synthesize drugs from scratch. Despite the billions of dollars spent in development, the long-awaited malaria drug, like many others, is stillborn in the lab. To compound matters, the FDA is cracking down on “me-too” drugs (existing formulas that, with a slight twist, can be sold under a different name). This prohibition makes it harder for drug companies to float financially while they wait for the next streptomycin.

  In the meantime, disease is having no trouble holding up its end of the arms race. Epidemiologists say we are living in “the emerging age of viruses,” battling new diseases like AIDS, while resistant strains of diseases that we thought we had under control, like tuberculosis and the bubonic plague, are back with a vengeance. Just when we need a breakthrough, we’ve reached a point of diminishing returns.

  Once again, hopes are being pinned on nature’s biochemical registry, which is billions of years in the making. “Given the high cost of chemical synthesis,” says Charles McChesney, a natural products chemist at the University of Mississippi, “companies are increasingly inclined to let plants and other organisms do the synthetic work for them.” In a flurry of exploration contracts, drug companies are heading outdoors to find their next big drug.

  Between 1990 and 1993, five major drug companies joined the medicinal gold rush, announcing large-scale plans to prospect in seven countries. Most recently, the National Institutes of Health and several drug companies began a $2.5 million treasure hunt in the Great Barrier Reef off Australia, in Samoa, and in the rain forests of South America and Africa. In this effort, marine biologists and botanists will spend five years collecting approximately fifteen thousand marine organisms and twenty thousand plants. Meanwhile, a $2 million, three-year effort begun in 1993 with Pfizer, Inc., and the New York Botanical Garden will concentrate on plants here in the United States. Also in the United States, the proposed Joint Program on Drug Discovery, Biodiversity Conservation, and Economic Growth would provide grants (funded by AID, NCI, and NSF) to develop drugs from the most promising plants. Meanwhile, a coalition of government agencies, nongovernmental organizations, and businesses both here and in Asia are collaborating to help local communities both use and preserve their forest and marine genetic resources. All told, a 1992 Office of Technology Assessment report listed some two hundred companies and nearly as many research institutions worldwide that are now looking for plants as sources of pharmaceuticals and pesticides.

  Will this usher in a new era of resource plundering? Chemical ecologist Thomas Eisner from Cornell University doesn’t think so. He believes that chemical prospecting can be essentially noninvasive both ecologically and culturally (as long as intellectual property rights are assigned to the local people—a system that was agreed upon at the 1992 United Nations Conference on Environment and Development in Rio). “On
ce biological activity is discovered,” Eisner writes, “the usual procedure is not to harvest the source organism, but to identify the responsible chemical so it can be produced synthetically.” For example, the natural opiates morphine and codeine were the models from which meperidine (Demerol), pentazocine (Talwin), and propoxyphene (Darvon) were then synthesized. Sampling for model design need not be extensive, says Eisner. In the case of “drugs from bugs,” chemists need only small quantities for screening—about half a kilo of insects, or what hits several windshields on a tropical summer evening.

  The last time many drug companies scoured the natural world for ideas was in the fifties. The jungles and reefs they will encounter in the nineties are very different—fragmented, fragile, and disappearing. Most frightening of all are reports that one in four wild species (includes all taxonomic categories) will be facing extinction by the year 2025. Underlying the new haste to find cures is the understanding that it may be now or never for chemical prospecting.

  The job ahead is enormous. Out of the estimated 5 to 30 million living species on Earth (some estimates put it closer to 100 million) only about 1.4 million have been named. Less than 5 percent of the world’s total roster of plant species have been identified, and out of the estimated 265,000 flowering species, only about 5,000, or 2 percent, have been studied exhaustively for chemical composition and medicinal value. To take one country as an example, scientists estimate that nothing is known about the chemistry of more than 99 percent of the plant species growing in Brazil.

  To light a lamp in this darkness, companies and governments are pouring into the remaining pristine jungles and oceans, collecting examples of what is left. Back home, lab workers attempt the arduous task of analyzing the mountains of diversity on their warehouse floors.