Wild chimpanzees drink two cocktails' worth of alcohol daily from boozy fruit, study finds

A new study finds wild chimpanzees in the forests of Uganda and Côte d’Ivoire consume roughly two cocktails’ worth of alcohol each day through overripe, fermented fruit. Researchers report chimps ingest about 14 grams of ethanol daily, drawn from roughly 10 pounds of fruit they eat, a total that translates to about two standard American drinks when scaled to a human body mass. The paper, published Wednesday in Science Advances by researchers at the University of California, Berkeley, outlines how alcohol enters the chimp diet across Kibale National Park in Uganda and Taï National Park in Ivory Coast.

To determine the chimps’ alcohol intake, scientists tested the ethanol content of fruit eaten by chimpanzees at Kibale National Park and Taï National Park. Across all sites, male and female chimpanzees are consuming about 14 grams of pure ethanol per day in their diet, which is the equivalent to one standard American drink, UC Berkeley graduate student Aleksey Maro of the Department of Integrative Biology told Berkeley News. When you adjust for body mass, because chimps weigh about 40 kilos versus a typical human at 70 kilos, it goes up to nearly two drinks, Maro said.

It is not clear exactly why the chimps seek out the particularly intoxicating fruits, which are typically riper and contain more sugars to ferment. But the findings suggest that alcohol is a regular part of chimps’ diets — and likely our ancestors, too. “The chimps are eating 5 to 10% of their body weight a day in ripe fruit, so even low concentrations yield a high daily total, a substantial dosage of alcohol,” UC Berkeley Professor Robert Dudley told Berkeley News. The findings suggest that alcohol is a regular part of chimps’ diets, and likely our ancestors, too.

Dudley is associated with the so-called drunken monkey hypothesis, which argues that humans’ alcohol-drinking habits have roots in our primate ancestors’ penchant for energy-rich, fermented fruit. Though the chimps are consuming an impressive amount of alcohol, they do not feel a buzz, researchers added. The apes would have to consume enough fruit to be bloated to feel intoxicated. “Chimpanzees consume a similar amount of alcohol to what we might if we ate fermented food daily,” Maro said. “Human attraction to alcohol probably arose from this dietary heritage of our common ancestor with chimpanzees.”

The study’s authors emphasize that the exact reasons chimpanzees seek out fermenting fruit remain unclear, but the work adds to a growing body of evidence that alcohol has long been intertwined with primate diets. While the ecological and physiological implications for chimpanzees require further study, the research raises provocative questions about how our own relationship with alcohol may have deep evolutionary roots.

Context from researchers and peers alike suggests that the phenomenon is likely not unique to chimpanzees or to these two parks. The discovery aligns with broader observations that energy-rich, fermenting fruits are a persistent feature of tropical forests and may have shaped feeding strategies, nutritional tradeoffs, and social behaviors over millennia. The researchers caution that more work is needed to understand how widespread the pattern is across chimpanzee communities and other primates, and what, if any, behavioral adaptations accompany regular exposure to ethanol in wild settings.