Deep in the forests of Guinea-Bissau, a camera trap captured something primatologists had never formally documented in wild, unhabituated chimpanzees: one adult picking up a chunk of naturally fermented fruit and handing it to another. Then it happened again. The footage, recorded in Cantanhez National Park and published in Current Biology in 2025, amounts to the closest parallel to social drinking ever observed among non-human primates, and it is forcing researchers to rethink how far back the roots of communal feasting really stretch.
What the cameras caught
The study, led by primatologist Kimberley Hockings of the University of Exeter, describes multiple events in which wild western chimpanzees (Pan troglodytes verus) fed on naturally fermented African breadfruit (Treculia africana), a large, starchy fruit that begins producing ethanol as it ripens and falls to the forest floor. On at least two occasions, adults actively shared pieces of the fermenting fruit with other adults, behavior recorded entirely through fixed camera-trap arrays with no human observers present.
That last detail matters. The Cantanhez chimpanzees are unhabituated, meaning they have never been conditioned to tolerate researchers at close range. The footage rules out the possibility that the animals were reacting to provisioned food or performing for an audience. What the cameras recorded was spontaneous, undisturbed behavior.
Adult chimpanzees almost never share plant foods with unrelated group members. Meat sharing after hunts is well documented, but handing over a piece of fruit is a different category of generosity, one that primatologists have long treated as a marker of social tolerance rather than simple caloric exchange. When one of these chimpanzees passed a chunk of fermenting breadfruit to another, it carried social weight that a mango never would.
How much alcohol is actually in the fruit?
Separate quantitative work at two long-term field sites, Tai Forest in Côte d’Ivoire and Ngogo in Uganda, has confirmed that ripe fruit pulp from multiple species routinely contains measurable ethanol concentrations, typically ranging from about 1% to 4% alcohol by volume in overripe or fallen specimens. For comparison, a light beer sits around 4% ABV. Researchers scaled those concentrations against observed feeding times and diet composition to estimate how much ethanol wild chimpanzees actually ingest during normal foraging. The conclusion: ethanol exposure through fruit is not a freak occurrence but a recurring feature of chimpanzee diets across geographically distant populations.
The Current Biology study does not include per-event ethanol assays on the exact Treculia africana fruits that were shared in Guinea-Bissau. The ethanol measurements from Tai and Ngogo come from different fruit species at different sites, so extrapolating precise alcohol intake for the Cantanhez chimpanzees requires assumptions that have not yet been tested directly. Still, the chemical evidence from multiple sites makes clear that wild chimpanzees are regularly encountering low-dose alcohol in their food.
An enzyme 10 million years in the making
None of this is happening by accident. Research published in Proceedings of the National Academy of Sciences by Matthew Carrigan and colleagues showed that ancestors of African great apes underwent a key change in their alcohol dehydrogenase (ADH4) enzymes roughly 10 million years ago, boosting their ability to metabolize ethanol by about 40-fold. That adaptation coincided with a shift toward more terrestrial lifestyles and greater exposure to fallen, fermenting fruit on the forest floor.
The Guinea-Bissau observations fit neatly into this evolutionary timeline. These chimpanzees are not stumbling into ethanol by chance. They are equipped by natural selection to process it, and they appear to seek out fermenting fruit deliberately.
Social drinking or just social eating?
The most provocative question the footage raises is whether sharing fermented fruit represents something meaningfully different from sharing any other food. A peer-reviewed synthesis connecting this kind of “scrumping,” feeding on fallen and fermenting fruit, to hypotheses about the evolutionary origins of social feasting frames the behavior as an ancestral precursor to human communal eating. The framing is intellectually provocative, but the authors present it as a hypothesis to test, not a settled conclusion.
In meat-sharing contexts, dominant chimpanzees often use food as a bargaining chip, trading access for grooming, coalitionary support, or reduced harassment. With plant foods, especially abundant ones, that kind of strategic trading is less common. Treculia africana fruits are large and clumped, creating temporary feeding hotspots, but they are not as rare or hard-won as a colobus monkey carcass. When one adult allows another to take a portion, it may be signaling tolerance, reinforcing an alliance, or simply avoiding a fight over a resource that cannot be monopolized for long.
What the footage does not show is drunken apes stumbling through the jungle. The concentrations found in wild fruit are generally low, and chimpanzee feeding bouts are spread across the day. The camera-trap recordings reveal no obvious motor impairment, no aggression spikes, no disinhibition. The animals appear focused on feeding and, intermittently, on negotiating access to the best pieces.
Because the Cantanhez chimpanzees are unhabituated, researchers cannot yet map these interactions onto detailed social networks. They do not know whether the individuals who share fermented fruit also groom each other frequently, cooperate during territorial patrols, or share other foods. Without that broader context, calling this “social drinking” in any human sense remains a stretch. But the behavior looks like a plausible precursor, and the underlying biology supports it.
What this changes about the story of alcohol
Even with the caveats, the convergence of behavioral, chemical, and evolutionary evidence is striking. Wild chimpanzees regularly encounter low doses of ethanol in their natural diet, possess enzymatic machinery well suited to metabolizing it, and sometimes pass ethanol-bearing foods from one adult to another. Those facts challenge the tidy narrative that alcohol is a purely cultural invention of agricultural societies. Instead, they suggest that the human relationship with fermented resources has deep biological roots, shaped by millions of years of primate foraging in patchy, seasonally variable forests.
Future fieldwork at Cantanhez and other sites will need to tighten the links between specific feeding events, ethanol loads, and social outcomes. That could mean pairing camera traps with systematic sampling of fallen fruits, or combining noninvasive biomarkers with long-term behavioral monitoring at habituated communities. As of June 2025, the Guinea-Bissau footage stands as an early, carefully documented glimpse into an ancient pattern: primates gathering around rich, occasionally fermented windfalls and, at least sometimes, choosing to share.
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*This article was researched with the help of AI, with human editors creating the final content.
