“There’s a learning process that needs to take place in order for them to develop a preference for foods that contain those medicines,” Villalba says. Tellingly, the sheep chose the medicated food only when they required it. When Villalba dewormed the infected animals, even those that had previously medicated themselves successfully avoided the bitter-tasting fare. They sensed that they didn’t need to self-treat. Villalba has also found that lambs and ewes learn about medicinal foods faster when they’re together (rather than alone), as if primed for a transfer of medicinal knowledge. This could explain how, once acquired, medicinal understanding is maintained in groups of animals.

Image Credit... Illustration by Kelsey Dake

The abiding question — the greatest puzzle of all, really — is how animals first learn which plants are medicinal. Villalba has observed that lambs infected with parasites are more likely to try new plants when grazing in an open pasture compared to uninfected lambs. They lose some of what scientists call food “neophobia,” the fear of new flavors, and their greater willingness to explore the surrounding foodscape may increase the odds of a medicinal discovery.

Huffman calls these tendencies “pre-adaptations.” They’re hard-wired behaviors that push animals toward the acquisition of medical knowledge — in this case, by impelling them to try the very flavors they normally shun. Arguably, this exploratory behavior exhibits a fundamental insight about the world, which, fully articulated, might go like this: Plants have evolved an exquisite array of poisons and noxious compounds to protect themselves. Many of these are directed at invertebrates and microbes, relatives of what makes an animal sick. So a terrible-tasting plant, one usually avoided, has a better-than-average chance of beating back whatever is making that creature ill.

Monkeys and apes and sheep aren’t performing surgery. They haven’t invented vaccines or figured out how to manufacture insulin. Even older medical traditions, like those in which Mohamedi Kalunde’s grandfather worked — informed by observation and developed through experimentation — are surely far more advanced than what animals manage to do. But they may still provide us with medical insights. Huffman points out, for instance, that while we tend to isolate just one molecule for our drugs, animals use plants that produce multiple antimicrobial and antiparasitic substances at once. By ingesting what’s really a drug cocktail, animals minimize the problem of antibiotic resistance.

Villalba’s research may have practical implications. Resistance to antiparasite medication is a growing problem for livestock and people alike. But if grazing animals are able to medicate themselves, perhaps ranchers should make a wide variety of plants available to them, rather than one or two types of feed. This might allow them to select the medicinal plants they need, improving their health and ultimately saving money spent on medicines. It would also theoretically lessen the risk of antibiotic-resistant superbugs emerging from livestock operations. Anecdotally, Villalba says, ranchers already report that livestock grazing in wilder, more diverse pastures are healthier than those confined to smaller spaces, possibly because they are able to self-medicate.

A similar approach might help the honeybees that are so important for crop fertilization and that have been dying at an alarming rate in recent years. Bees collect resins from certain trees to protect themselves against infection, a form of social immunity or communal self-medication. But these days, with sources of resin scarce in agricultural settings, honeybees may lack those defenses, says Marla Spivak, an entomologist at the University of Minnesota. The unavailability of resins could be one factor making them vulnerable to disease.

It’s worth considering the ways that animals, precisely because of their more limited intellects, might be more doggedly scientific than we are. After all, while animals seem to attend closely to cause and effect, learning from experience, people sometimes indulge a penchant for spinning out grand theories from scant (or no) evidence and then acting on them. Bloodletting, for example, persisted for hundreds of years in Europe even though it almost certainly weakened and killed the sick. It was based on the ancient humoral theory of disease: Illness arose when the body’s “humors,” or essential fluids, were out of harmony, an imbalance corrected by draining blood, among other acts. Other ineffectual and even dangerous treatments include smoking to treat asthma and sexual intercourse with virgins as a cure for syphilis.