Two Tai chimpanzees in Ivory Coast with fruit in their mouths. (Photo: Alexey Maro and the Tai Chimpanzee Project)
Early estimates of alcohol consumption suggest that wild chimpanzees may consume the equivalent of a pint of beer and half their daily alcohol intake from fruits containing alcohol.
Thanks to a fruit-rich diet and natural fermentation, chimpanzees (Pan troglodytes) in Uganda and Côte d'Ivoire likely consume about 0.5 ounces (14 grams) of ethanol per day.
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“They definitely don't get drunk,” study co-author Alexey Maro, a primatologist at the University of California, Berkeley, told Live Science. “Even if you drank two cocktails during the day, you wouldn't feel anything.”
The idea that humans are drawn to alcohol because it naturally appeared in our diets is called the “drunk ape hypothesis” and was advanced by study co-author Robert Dudley, a professor of integrative biology at the University of California, Berkeley. Dudley's hypothesis suggests that at a certain point in primate evolution, our early ancestors were unable to process fermented fruits and were therefore deprived of high-calorie foods.
To utilize this nutritional resource, primates evolved the ability to retain fluid by breaking down ethanol.
However, until now, scientists have only directly observed chimpanzees eating fruits containing ethanol once. In 2022, chimpanzees in Guinea-Bissau ate and shared naturally fermented African breadfruit.
“I, like everyone else, am skeptical of the drunken monkey hypothesis, so I tried to do my own investigation,” Maro said.
To determine how regularly chimpanzees consume ethanol-rich fruits, Marot and his team monitored two groups of chimpanzees: the Ngogo chimpanzees in Uganda and the Tai chimpanzees in Côte d'Ivoire. They observed the chimpanzees over three, multi-month periods from 2017 to 2021.
The researchers collected samples of freshly fallen fruit whenever they encountered it while eating. They ultimately recovered 254 ripe fruit samples from 15 species in Ngogo and 245 samples from six species in Tai.
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To estimate the alcohol content of the samples, the team either analyzed the alcohol vapor found inside the fruit or used a chemical reagent that turned yellow when in contact with ethanol.
They found that Ngogo's chimpanzees ate fruit with an average ethanol concentration of 0.32%, meaning there was 1.1 ounces (32 grams) of ethanol for every 3.5 ounces (100 grams) of total weight. The fruit eaten by Tai's chimpanzee had a remarkably similar average ethanol concentration of 0.31%.
Maro and his team then used previously obtained data on chimpanzee diet and body weight to estimate the daily ethanol consumption of both populations. They found that both male and female chimpanzees consumed approximately 0.5 ounces of ethanol per day, which is equivalent to about 2.5 standard drinks, adjusted for their smaller sizes.
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Matthew Carrigan, a molecular biologist at the College of Central Florida who was not involved in the study, noted that while the results aren't necessarily surprising, they are encouraging because they advance “an important question about evolution and human dependence on ethanol.”
However, Carrigan noted that “the error range is very wide,” meaning the chimpanzees could have consumed anywhere from 0.14 ounces (4 grams) of ethanol per day to 0.85 ounces (24 grams)—a difference of less than one drink to four.
Maro also acknowledged that the samples studied could have been fruits that the chimpanzees refused to eat. The next step is to determine whether chimpanzees avoid individual fruits or prefer them depending on their degree of fermentation, Carrigan said.
Ultimately, humans and chimpanzees “evolved to get calories without getting drunk,” Carrigan said. “Otherwise, if we had evolved to get drunk, we wouldn't have been able to metabolize ethanol as quickly.”
Sophie Berdugo, Social Link Navigator, Live Science Contributor
Sophie is a UK-based staff writer for Live Science. She covers a wide range of topics, having previously covered research ranging from bonobo communication to the first water in the universe. Her work has also appeared in publications such as New Scientist, The Observer, and BBC Wildlife, and her freelance work for New Scientist was shortlisted for the 2025 Association of British Science Journalists' Newcomer of the Year Award. Before becoming a science journalist, she earned a PhD in evolutionary anthropology from Oxford University, where she spent four years studying why some chimpanzees are better tool users than others.
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