Mushrooms may not be the first food that comes to mind when we imagine the diets of wild primates – or our early human ancestors. We tend to think of fruits and green leaves as the preferred foods for monkeys and apes.

But our new study from the Issa Valley in western Tanzania highlights a surprising, and potentially crucial, role for fungi in primate diets.

For nearly two decades, our work has centred on what it means to be a savanna-woodland primate in east Africa. Far from their forest-dwelling cousins, these populations are exposed to higher temperatures, as well as woodland and grassland vegetation where they can find food – or be in danger from predators like wild dogs and hyenas.

Broadly, we are interested in competition between species. For example, how do baboons and smaller monkeys avoid larger (and predatory) chimpanzees when looking for ripe fruits? Mushrooms may provide an answer.

We found that while all three primate species under study consumed mushrooms, their use and reliance differed throughout the year. Mushrooms were seasonally important for red-tailed monkeys and chimpanzees, becoming a fall-back food when ripe fruit was scarce, despite overall making up only 2% of their diet. For baboons, mushrooms were a preferred food, with fungi forming more than a tenth of their diet despite being available for only half the year.

Our findings not only shed light on the way that primates rely on and respond to their environment, but also hint at the evolutionary roots of human mycophagy (mushroom eating). Fungi have been overlooked in research into ancient diets because they don’t fossilise well and leave little trace in the archaeological record.

By examining which foods are consumed by primates, we can better reconstruct scenarios of how early human species may have competed with one another.

Issa fungi foraging

Over four years, we observed three co-inhabiting species – chimpanzees, yellow baboons and red-tailed monkeys – regularly consuming mushrooms.

We used over 50,000 observations of feeding among the three species and found that mushroom consumption wasn’t just incidental. While chimpanzees and red-tailed monkeys ate mushrooms mostly during the wet season, when availability peaked, baboons consumed mushrooms far longer, even when they were relatively scarce.

In fact, for two months of the year, mushrooms made up over 35% of baboons’ diets, suggesting they are a preferred food, not just consumed during fruit-scarce periods, as we suggest for the chimpanzees and red-tailed monkeys.

Chimpanzees and red-tailed monkeys, in contrast, treated mushrooms as a seasonal supplement, valuable when fruits were less abundant. This nuanced difference suggests that mushrooms play different roles within this primate community, depending on ecological strategies and competition dynamics.

Avoiding conflict through fungi

One of the most intriguing ideas to emerge from our study is the concept of niche partitioning: how animals adapt their diets to minimise competition. This is a well-established phenomenon which can manifest in various ways, from bird species occupying different canopy heights, to carnivores targeting different prey.

In habitats where multiple species coexist, finding one’s own food niche can be the key to survival. At Issa, baboons, chimpanzees and guenons (monkeys) might all be using mushrooms in strategic ways to improve feeding efficiency and reduce tension with each other as they respond to periods when (preferred) ripe fruits are insufficient for all three species.

What does this mean for us?

The implications of these findings stretch far beyond western Tanzania. First, they highlight how mushrooms can serve as a rich, seasonal food source, even for large mammals, providing protein, micronutrients and potentially medicinal benefits. This lends support to theories that fungi may have played a significant role in the diets of early hominins.

In fact, the habitat of Issa is thought to resemble the kind of mosaic woodland landscape where human ancestors evolved. If our primate relatives today are exploiting fungi in this environment, it’s plausible that Australopithecus, Homo habilis and other early human species did too.

Despite this, fungi are often overlooked in reconstructions of ancient diets, largely because they don’t fossilise well and leave little trace. Yet ancient DNA from Neanderthal dental plaque from about 40,000 years ago has revealed traces of mushrooms, tantalising clues that fungi may have been more central to prehistoric life than previously believed.

A caution and a call

The study also raises important questions about human-wildlife coexistence. In many parts of Tanzania, mushrooms are harvested by people and sold in local markets. As climate change and human population growth put pressure on wild resources, competition between humans and wildlife over edible fungi may increase. Understanding who eats what and when could help in managing these shared resources sustainably.

At a time when biodiversity is under threat and food security is a growing global concern, this research reminds us that hidden treasures like wild mushrooms aren’t just tasty; they’re significant for ecology and evolution.

Fungi can add to our understanding of where we came from and how we might share our ecosystems going forward.