In April 2025, researchers from the University of Exeter published footage that had been sitting in their camera traps since 2022. Wild chimpanzees in Cantanhez National Park, Guinea-Bissau, were sharing naturally fermented African breadfruit. Not eating it side by side, as chimps do with most plant food, but sharing it. Passing it between adults, including unrelated individuals, tolerating others feeding from fruit they were holding. This was documented on ten separate occasions involving seventeen individuals. In nine of the ten events, the sharing was passive: a possessor simply allowed others to feed. No aggression. No sharing under pressure.

Chimpanzees share food far less often than humans do, and when they do, it is almost always meat. Plant food sharing is rare enough to be noteworthy on its own. What made this footage striking was that 90% of the shared fruit contained measurable ethanol, ranging from 0.01% to 0.61% ABV. The researchers could not prove the ethanol caused the sharing. But they noted it, carefully, as a possibility worth taking seriously.

Credit for bringing this study to wider attention goes to Matthew Deller MW, whose LinkedIn article flagged the research shortly after publication.

The evolutionary wiring

The Cantanhez sharing observations add to evidence that low-level ethanol exposure in primates has deep roots. The drunken monkey hypothesis, first proposed by Robert Dudley of UC Berkeley, argues that primate attraction to ethanol is not accidental. Our frugivorous ancestors evolved in environments where fermenting fruit was a reliable signal: high calorie content, ripeness, energy. The smell of ethanol meant food worth having. Over millions of years, that association went deep.

In 2015, Carrigan et al. published a study in PNAS that found a single mutation in the ADH4 enzyme, occurring approximately ten million years ago, which gave hominid ancestors a 40-fold enhanced ability to metabolise ethanol. This coincides with the shift to a more terrestrial lifestyle and increased exposure to fermented fruit on the forest floor. The adaptation preceded human-directed fermentation by millions of years. We were processing ethanol long before we were brewing it.

In September 2025, Maro et al. published a follow-up in Science Advances measuring ethanol in wild chimpanzee diets at Kibale National Park in Uganda and Taï National Park in Côte d’Ivoire. They estimated that typical fruit consumption in those populations could correspond to the ethanol equivalent of roughly 1.4 standard drinks per day.

The hypothesis has never claimed that our ancestors were getting drunk. It suggests that low-level ethanol exposure was chronic and routine in primate life. And crucially, in a social species, that exposure happened in groups.

We were built for this. Just not for what we turned it into.

How we lost the ritual

Edward Slingerland, in his 2021 book Drunk, argues that alcohol functioned for thousands of years as a social technology: a tool for reducing inhibition, signalling trust, and enabling cooperation between people who would otherwise have had little reason to lower their guard. The evidence for this is cross-cultural and anthropological. Greek symposia were not drinking parties in the modern sense. They were structured occasions with a designated moderator, the Symposiarch, whose job was to manage the wine, water it down, and keep the proceedings functional. The drinking was in service of the conversation, not the point of the evening. Georgian supras unfold over hours of toasts and storytelling, each toast a small ceremony. The drink has a container.

In modern times, that structured, social container has largely disappeared. Drinkaware’s 2026 report on home drinking, drawing on Monitor data from 2018 to 2025 and Kantar purchasing figures, found that 73% of all alcohol sold in 2023 was bought in the off-trade, up from 53% in 2000. Two in five UK adults now drink at home on a weekly basis. One in five drink weekly in pubs, bars or restaurants. Weekly alcohol purchases for consumption outside the home have fallen by roughly two thirds since the mid-2000s. According to the British Beer and Pub Association, more than 2,000 pubs have closed since 2020.

The social infrastructure around drinking has contracted. What replaced it is private, available, cheap, and structureless.

A 2025 study by Wilson et al. in the Journal of Studies on Alcohol and Drugs, analysing 271,738 drinking occasions reported by 83,952 adult drinkers in Great Britain, found that solitary drinking was associated with being male, being over 50, and living alone, and was also associated with higher-risk drinking profiles. The association does not establish that drinking alone causes the risk; it shows the two consistently appear together. The mechanism is not complicated: social drinking has guardrails built in. Other people’s eyes on the glass, the natural pacing of conversation, the implicit norms of an occasion. Solitary drinking removes those guardrails.

This does not mean social drinking is safe or that drinking with others solves anything. Plenty of harmful drinking happens in company. What matters is not who is in the room but whether the drinking has structure and purpose, or whether it has become automatic.

The autopilot trap

Behaviours become automatic when they are repeated in a stable context with a consistent cue and a reliable reward. The basal ganglia encodes the sequence and runs it faster than the prefrontal cortex can intervene. Modern home drinking is the perfect substrate for this process.

The context is stable: the same sofa, the same time of evening, the same activity on the television. The cue is reliable: the end of the working day, a particular feeling of tiredness, a particular tension that wants releasing. The reward is immediate: the neurochemical effect of the first drink, the conditioned sense that the evening has begun. The pour becomes reflexive before the decision has been made.

Grey-area drinkers often cannot explain why they drink as much as they do. Not because they lack insight but because the habit is running below the level where insight normally operates. The chimps in Cantanhez National Park were sharing fermented fruit in a social context with apparent purpose. The modern grey-area drinker is often doing the opposite: drinking alone, repeatedly, in a context engineered by routine rather than intention, with the original social function entirely absent.

The distance between those two pictures is not a moral failing. It is a structural one.

Intentional drinking is not less drinking

The answer to autopilot drinking is recovering the conditions that make drinking a choice rather than a reflex.

What the historical examples share is not moderation in the modern, anxious sense. The Symposiarch did not ration wine because wine was bad. He managed the occasion because the occasion had a purpose, and the wine was in service of it. The Georgian supra does not end after two glasses. It ends when the evening is complete. The drink follows the intention, not the other way around.

For a grey-area drinker whose drinking has become private, habitual, and disconnected from any particular occasion or purpose, the task is not to drink less in the abstract. It is to rebuild the frame around drinking that modern life has quietly removed.

Curious what your own drinking is actually costing you, in spend, calories and sleep? The ARC Alcohol Real-Cost Calculator takes about three minutes and runs entirely in your browser.

The BAC System™: rebuilding the frame

For many grey-area drinkers, alcohol has moved from an occasion into a private routine. A glass poured on the sofa can become less a conscious choice than an automated habit.

The BAC™ (Balance and Control) System was built for exactly this situation: grey-area drinkers whose consumption has shifted from deliberate choice to autopilot routine. It maps your actual triggers, identifies what is running the pattern, and gives you a flexible framework that adapts to real life rather than collapsing the first time things get messy.

A shifting mindset is part of that. Sustainable moderation means learning to treat slip-ups as data rather than judgement. The BAC System™ is not a course to complete and leave behind. It is an operating system for living with more intention, flexibility, and control.

A note on safety

This article is written for adults who drink above guidelines but are not clinically dependent. The evolutionary context discussed above does not make alcohol harmless, and it does not make heavy drinking a biological inevitability. If you are concerned about your drinking, find it difficult to cut down, or are worried about stopping, please speak to your GP or contact WithYou, a free and confidential support service: wearewithyou.org.uk.

References

Bowland AC, Bersacola E, Ramon M, Bessa J, Melin AD, Carrigan MA, Harrison XA, Hockings KJ. Wild chimpanzees share fermented fruits. Current Biology. 2025;35(8):R279. DOI: 10.1016/j.cub.2025.02.067

Maro A, Sandel AA, Blaiore BZA, Wittig RM, Mitani JC, Dudley R. Ethanol ingestion via frugivory in wild chimpanzees. Science Advances. 2025;11(38):eadw1665. DOI: 10.1126/sciadv.adw1665

Carrigan MA, Uryasev O, Frye CB, Eckman BL, Myers CR, Hurley TD, Benner SA. Hominids adapted to metabolize ethanol long before human-directed fermentation. PNAS. 2015;112(2):458-463. DOI: 10.1073/pnas.1404167111

Drinkaware. Drinking at Home: Changing patterns and opportunities for prevention. March 2026. Available at: drinkaware.co.uk

Wilson LB, Bain M, Hernández-Alava M, Holmes J, Pryce R, Sasso A, Stevely AK, Warde A, Meier PS, et al. Solitary drinkers in Great Britain: how do their sociodemographic characteristics, consumption patterns, and drinking occasions differ from those who drink with others? Journal of Studies on Alcohol and Drugs. 2025;86(1):39-47. DOI: 10.15288/jsad.23-00408

Slingerland E. Drunk: How We Sipped, Danced, and Stumbled Our Way to Civilisation. Little, Brown Spark; 2021.

British Beer and Pub Association. Pub closure data 2020-2025. Available at: beerandpub.com