Wild chimpanzees have been found to consume the equivalent of a glass of beer a day through fermented fruit. Like humans who enjoy a beer after work, chimpanzees are essentially having "a light drink" every day.
A research team at the University of California, Berkeley (UC Berkeley) said on the 17th (local time) in the international journal Science Advances that "measuring the alcohol content of the fruit wild chimpanzees eat in a day confirmed that it contains about 14 grams of pure ethanol." That amount of alcohol is about the level of one glass of beer (355 mL).
Unlike the fruit we buy and eat, the wild fruit that chimpanzees eat contains trace amounts of alcohol. This is the result of sugars turning into ethanol by yeast through natural fermentation. In particular, tropical and subtropical fruits with high sugar content, such as figs, grapes, and plums, naturally contain about 0.1–0.5% alcohol.
The researchers directly measured ethanol concentrations in fruit that make up a significant part of the chimpanzee diet. An analysis of the pulp of 20 species of flowering plants (angiosperms) from two regions in Uganda and Côte d'Ivoire in Africa found an average ethanol level of 0.31–0.32%. Given that chimpanzees consume an average of 4.5 kg of fruit per day, they can be seen as ingesting about 14 grams of ethanol daily.
According to the researchers, chimpanzees in Uganda mainly ate figs, while those in Côte d'Ivoire mainly ate Guinea plum from the plum family. Robert Dudley, a professor of biology at UC Berkeley, said, "The alcohol concentration in fruit is low, but because chimpanzees consume so much fruit, they end up ingesting a considerable amount of alcohol."
Professor Dudley said chimpanzees' alcohol intake supports the "drunken monkey" hypothesis. The hypothesis holds that humans' drinking tendencies stem from the habits of primate ancestors who sought out energy-rich fermented fruit. He said, "A major factor behind humans' liking for alcohol is this 'dietary heritage.'"
This study is not the first to capture chimpanzees' drinking habits. According to the results of a 17-year study in a village in Guinea, West Africa, wild chimpanzees were observed drinking fermented palm sap 51 times. On Apr. 4, researchers at the University of Exeter in the United Kingdom said they filmed a group of wild chimpanzees sharing naturally fermented fruit 10 times in Cantanhez National Park in Guinea-Bissau, Africa.
Animals drunk on alcohol have often been featured. Scenes of animals consuming alcohol produced as fruit or honey ferments naturally, then staggering or suffering hangovers, have been captured from time to time. In the past, this was considered accidental, but recently scientists believe chimpanzees intentionally gather to drink.
Professor Dudley said, "It is interesting that even if chimpanzees drink alcohol every day like humans, no external signs such as flushed faces or appearing intoxicated were observed," adding, "For chimpanzees to fully feel the effects of alcohol, they would have to eat fruit until their bellies are distended."
The researchers are currently conducting urine analyses to determine how much alcohol chimpanzees actually carry in their bodies.
References
Science Advances (2025), DOI: https://doi.org/10.1126/sciadv.adw1665
Current Biology (2025),https://www.cell.com/current-biology/fulltext/S0960-9822(25)00281-7
Royal Society Open Science (2015), DOI:
https://doi.org/10.1098/rsos.150150