A new study suggests chimpanzees consume alcohol regularly in fruit. Researchers at UC Berkeley measured ethanol in fruits from African habitats. The findings hint at a shared dietary history with humans.
How Much Alcohol Do Chimpanzees Consume?
Chimpanzees at Ngogo in Uganda and Taï in the Ivory Coast eat a variety of ripe fruits. The team measured 21 fruit species for ethanol content. On average, the fruits contained about 0.26% alcohol by weight.
Primatologists estimate chimps eat roughly 4.5 kilograms of fruit daily. This amount makes up about three-quarters of their diet. Males and females consume around 14 grams of ethanol per day. Adjusted for body weight, it equals nearly two standard drinks daily.
“This is similar to what humans would drink when eating fermented foods,” said Aleksey Maro, a UC Berkeley graduate student. “Daily low-level exposure probably shaped our shared evolutionary history.”
Does Alcohol Affect Chimpanzees’ Behaviour?
Despite chronic exposure, chimps show no overt signs of intoxication. They would need to overeat fruit to feel any buzz. Low-level consumption is likely part of natural diet patterns. Alcohol may have been present in human diets millions of years ago.
Robert Dudley, a UC Berkeley professor, noted that the daily ethanol intake is substantial. “Even low alcohol percentages add up given the amount eaten,” he said. The research provides evidence that alcohol is a regular dietary component.
How Was the Study Conducted?
Maro collected undamaged fruits under trees recently foraged by chimps. At Ngogo, chimps climb trees to pluck figs, the most popular fruit. At Taï, chimps eat mainly fallen fruit from the forest floor.
The team used three methods to measure alcohol content. These included a portable gas chromatograph, a breathalyser-like device, and chemical tests. All methods recorded similar ethanol percentages, confirming the results.
To account for diet composition, researchers weighted ethanol levels by species consumption. The most frequently eaten fruits had the highest alcohol content. Male chimps often gathered in Ficus musuco trees before patrols. The fruit of Parinari excelsa also attracted elephants in the same regions.
What Does This Mean for Humans?
The findings support the “drunken monkey” hypothesis, first proposed by Dudley. It suggests humans inherited an attraction to alcohol from primate ancestors. Other studies show captive primates prefer alcohol-rich nectar or fruit. Birds and other fruit-eating animals also consume dietary ethanol regularly.
Ethanol may signal sugar-rich food or enhance the pleasure of eating. It may also play a role in social bonding among primates. Dudley emphasised that this research highlights deep evolutionary roots of alcohol consumption.
Next Steps in Research
Maro returned to Ngogo this year to collect chimpanzee urine samples. Researchers analysed alcohol metabolites using field-ready test kits. They also collected freshly dislodged canopy fruits to measure ethanol content. The dataset now allows more precise studies on chimpanzee alcohol preferences.
“This study is the first to measure alcohol in wild fruits directly,” Dudley said. “It sets the foundation for future research on ethanol consumption in animals.”
The study by Maro and Dudley will appear in Science Advances on September 17, 2025.
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