To read the original article in full go to : Chimpanzees ingest more than the equivalent of one alcoholic drink a day – new research.
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Chimpanzees May Drink the Equivalent of Two Alcoholic Drinks Daily from Fermented Fruit, Study Finds
According to a study reported by The Guardian, wild chimpanzee communities in Africa may ingest the equivalent of two US standard alcoholic drinks each day by consuming high‑alcohol ripe fruits. Researchers led by Aleksey Maro of the University of California, Berkeley, analyzed more than 200 fruit samples from about 20 preferred trees and found substantial variation in alcohol content. The chimps’ daily intake, about 14 grams of alcohol, highlights how their fruit‑driven diet can include meaningful ethanol amounts, though their stomachs and body size (roughly 40 kg) likely prevent intoxication in most cases. This work also revisits the drunken monkey hypothesis, suggesting alcohol exposure could have shaped evolution and social behavior. Source: The Guardian.
Overview
New research on wild chimpanzees in eastern and western Africa suggests they may routinely ingest alcohol by feeding on fermented fruits, with daily ethanol intake estimated at about 14 grams, roughly equivalent to two US standard drinks. The study, led by Aleksey Maro of the University of California, Berkeley, involved collecting more than 200 fruits from around 20 of the chimps’ favored trees and measuring their alcohol content, revealing large variation among fruits and among individuals’ choices. The authors note that some fruits, particularly figs and plums, tend to be high in alcohol content, and contradicts the assumption that chimp diets are alcohol‑free. "The fruits most enjoyed by chimpanzees tend to have very high alcohol content" - Aleksey Maro, University of California, Berkeley.
Methodology and Key Findings
The researchers documented that chimpanzees can consume up to 4 kg of fruit daily, which translates to roughly 14 g of ethanol per day. This amount aligns with about two US standard drinks, acknowledging that standard drink definitions vary by country. The study emphasizes that direct human–chimps comparisons are imperfect because alcohol potency scales with body size. With chimps weighing around 40 kg on average, their ethanol intake represents a substantial, but not intoxicating, portion of their diet. "Chimps consume roughly 14 grams of alcohol per day, which corresponds to two US standard drinks" - Aleksey Maro, UC Berkeley.
Evolutionary Context and the Drunken Monkey Hypothesis
The findings feed into what Robert Dudley long proposed as the drunken monkey hypothesis, which posits that alcohol consumption from ripe fruits may have provided evolutionary advantages by signaling energy and sugar content. The study also notes that the human-appropriate enzymes used to metabolize alcohol were already present in our common ancestors with great apes around 10 million years ago, suggesting a deep evolutionary history for alcohol metabolism. "Alcohol in ripe fruits can indicate energy-rich sugars, offering an evolutionary advantage" - Robert Dudley.
Sociability and Behavioral Implications
Beyond nutrition, researchers observed signs that alcohol consumption may influence social behavior, with documented instances of chimps bonding over fermented fruits. In April 2025, footage from Guinea‑Bissau highlighted groups feasting on ripe breadfruit containing alcohol, hinting at social drinking dynamics. The researchers caution that the high volume of liquids and foods ingested by chimps can keep stomach fullness high, potentially preventing intoxication despite ongoing consumption. "Researchers also think that alcohol might make them more sociable" - The Guardian.
Implications, Limitations, and Next Steps
These findings add credibility to the idea that alcohol exposure is more widespread in nature than previously appreciated and may play a subtle role in primate ecology and evolution. However, the authors stress caution when extrapolating to humans, given differences in metabolism, behavior, and dosing. They also acknowledge variation across chimp communities and fruit availability, which could influence daily intake. The study contributes to a broader understanding of how fermented foods shape animal behavior and evolution, as well as the potential for ethanol to influence social dynamics in wild populations.
Full content
Drinking more than you intended may be something that many humans do, but now research is showing that a taste for alcohol is surprisingly common among animals. In fact a new study has found that chimpanzees may ingest the equivalent of two alcoholic drinks a day from eating fermented fruit.
In the last ten years or so, there has been growing evidence that the ingestion of alcohol might be more widespread across the animal kingdom than previously thought. Fruit flies, for example, lay their eggs in alcohol-rich fermented fruits, which offer the newly hatched larvae nutrients to feed on.
In 2015, scientists observed groups of chimpanzees in west Africa drinking large amounts of raffia palm alcoholic sap harvested by the local villagers. More recently, in April 2025, a population of chimpanzees at Guinea-Bissau were recorded feasting on ripe African breadfruits which contained high concentrations of alcohol.
The published studies mark a shift because evidence of alcohol consumption in wild animals tends to rely more on anecdotal observations. In Sweden, a moose made the news in 2011 when it was found stuck in a tree, apparently drunk from eating fermented apples.
And vervet monkeys in St Kitts, whose ancestors were brought there with enslaved people from west Africa, are often spotted stealing fruity cocktails from tourists.
The new study, led by biologist Aleksey Maro of the University of California, Berkeley, offers insights into how much alcohol is in the ripe fruits favoured by two wild chimpanzee communities living in eastern and western Africa.
Having spent almost a year studying chimpanzees in the wild myself, I have always been mesmerised by how excited they get when they spot their favourite fruits. Chimpanzees go crazy for fruit. They rush over to grab them and stuff their mouths full, all while making joyful noises of appreciation.
In their research, Maro and his colleagues collected more than 200 fruits from about 20 of chimpanzees’ favourite trees. They found large variation in alcohol content with some having zero or nearly zero alcohol content. But some of the fruits most enjoyed by the chimps, such as figs and plums, tend to have a very high alcohol content.
This suggests that chimps may intentionally select fruits for their high levels of alcohol. Because of the large quantity of fruits chimpanzees can eat every day (up to 4kg), the authors worked out that both female and male chimps consume roughly 14 grams of alcohol per day. This corresponds to a standard US alcoholic drink (UK standard drinks contain eight grams of alcohol).
Chimpanzees have a strong liking for fruit. Michaela Pilch/ShutterstockBut it’s not fair to directly compare these numbers between humans and chimps since the effect of alcohol depends on how big an individual is. Alcohol tends to be less potent in bigger people.
With an average weight of around 40kg, chimps tend to be smaller than humans. So the amount of equivalent alcohol that chimps consume actually corresponds to two American standard drinks per day. It sounds like chimps know how to have a party.
The drunken monkey hypothesis
Twenty-five years ago, Robert Dudley, who is one of the authors of the new study, proposed the “drunken monkey hypothesis”. This suggests that alcohol consumption in humans might have an ancient history. Dudley’s idea is that ingesting alcoholic fruits might have given an evolutionary advantage to animals. The alcoholic content in fruits can, for example, indicate to animals which ones are rich in energy and sugar.
Drinking alcohol can be good for health. Fruit flies, for example, ingest alcohol to kill parasites. Even in humans, studies have shown that low levels of alcohol consumption may reduce the risk of heart disease.
Support for the drunken monkey hypothesis came from research showing that the proteins humans need to break down alcohol in their body was already present in the common ancestor we share with gorillas, chimpanzees and bonobos that lived 10 million years ago.
This was a time when African forests started shrinking, and apes started coming down from the tree, adopting a more land-based lifestyle. It’s possible that these apes gained an advantage in eating ripe fermented fruits that had fallen onto the ground, avoiding the competition with other fruit-eating animals who could eat unripe fruit on trees.
Researchers also think that alcohol might make them more sociable. Chimpanzees in west Africa, for example, were observed in April 2025 eating and drinking fermented fruits together.
However, according to Dudley, in addition to having the same human protein that breaks down alcohol, chimpanzees may drink alcohol in low concentrations due to the high volume of liquid and food they ingest. So their stomach may fill up before alcohol reaches intoxicating levels.
This would explain why, in the 11 months that I spent watching chimps in Tanzania, I didn’t once see them wobbling around the forest, clutching a juicy fruit while laughing uncontrollably.