Chimpanzees & Alcohol: Study Links Fruit-Eating to Human Attraction to Drinking

For 11 days in late summer 2025, researcher Aleksey Maro found himself in the Ugandan rainforest, collecting chimpanzee urine. It sounds unusual, but the effort is part of a study attempting to understand the evolutionary roots of human attraction to alcohol. New research, published recently in Biology Letters, suggests that chimpanzees consume a significant amount of alcohol when they eat ripe, fermenting fruit – potentially offering clues about why humans developed a taste for intoxicating beverages.

The Drunken Monkey Hypothesis

Maro, a PhD student at the University of California, Berkeley, and his colleagues discovered that urine samples from 17 out of 19 chimpanzees tested positive for ethanol. At least ten of those samples contained concentrations equivalent to one or two alcoholic drinks in humans. Whereas this doesn’t mean the chimps are getting drunk, it does suggest regular alcohol consumption through their diet. This finding lends support to the “drunken monkey hypothesis,” which proposes that primates’ attraction to fermented fruit – and the alcohol it contains – isn’t accidental. Instead, it may be an evolutionary adaptation.

The theory posits that the scent of fermentation signals the presence of sugars, a valuable energy source. In other words, a whiff of alcohol might have historically guided primates to calorie-rich food. This could explain why humans, and perhaps our ancestors, developed a predisposition to enjoy alcoholic beverages. As Maro explains, this could represent “a profound mismatch between the way we live today and the way we evolved.”

Collecting the Evidence: A Delicate Process

Gathering the necessary samples wasn’t easy. The team employed several techniques, including carefully pipetting urine off leaves. Perhaps more challenging – and slightly precarious – was catching urine droplets as they streamed down from chimps in the trees using plastic bags stretched over forked branches.

“You need to make sure that you are not going to be splashed,” says Sharifah Namaganda, a PhD candidate at the University of Michigan who assisted Maro in the field. Namaganda, a Leakey Foundation Baldwin Fellow from Uganda, has extensive experience collecting samples at Ngogo, the Ugandan forest where the study took place. She emphasizes the reward of obtaining a clean sample: “But plastic-bag pee is the best you can get. And This proves too the sample that will make you most proud!”

The chimps were observed consuming African star apples, a fruit known to contain ethanol. Maro’s team then quickly analyzed the urine samples to determine if the chimps had metabolized the alcohol from the fruit. The average chimpanzee consumes around ten pounds of fruit pulp daily, making this a potentially significant source of ethanol intake.

Beyond Chimps: A Broader Evolutionary Picture

The study’s findings aren’t limited to chimpanzees. Maro points out that fruit flies also lay their larvae in fermenting fruit pulp, with a preference for higher alcohol concentrations. This suggests that an attraction to fermentation may be a deeply ingrained evolutionary trait, extending beyond primates.

Matthew Carrigan, an evolutionary biologist at the College of Central Florida who was not involved in the research, calls the study “wonderful.” He praises the work for building on earlier suggestions and providing direct measurement of alcohol metabolites. You can find more about his work here.

What Does This Mean for Humans?

While the study doesn’t suggest chimps are intentionally seeking intoxication, it raises the possibility that our ancestors may have developed a preference for the taste and aroma of fermented fruits. This preference could have then evolved into the modern human attraction to alcohol, which we now have the ability to concentrate to much higher levels.

Cat Hobaiter, a primatologist at the University of St. Andrews who wasn’t involved in the study, believes the research could open new avenues for understanding both chimpanzee behavior and the evolutionary origins of human rituals and social practices. More information about her research can be found at Wild Minds.

Future Research and Unanswered Questions

Maro’s next step is to determine whether chimpanzees are actively seeking out fruits containing ethanol, or simply consuming them as part of their regular diet. Evidence of intentional selection would strengthen the argument for a genuine preference for the taste or smell of fermented fruit.

The study’s relatively small sample size (19 chimps) is a limitation. Larger studies, encompassing a wider range of chimpanzee populations and fruit types, will be needed to confirm these findings and explore the nuances of alcohol consumption in primates. Further research could also investigate the genetic basis of alcohol metabolism in chimpanzees and humans, potentially shedding light on the evolutionary history of our relationship with alcohol.

The findings also highlight the importance of considering the evolutionary context when addressing issues related to alcohol consumption in humans. Understanding the deep-rooted biological factors that contribute to our attraction to alcohol may be crucial for developing effective prevention and treatment strategies. For more information on responsible alcohol consumption, consult resources from the National Institute on Alcohol Abuse and Alcoholism (NIAAA).