Chimpanzees’ Daily Alcohol Intake Confirmed by Urine Tests
New research confirms that chimpanzees regularly consume alcohol through fermented fruit, supporting the “drunken monkey hypothesis” regarding the evolutionary origins of primate alcohol consumption. Analysis of urine samples from wild chimpanzees in Uganda reveals the presence of ethanol byproducts in the majority of samples tested.
The Drunken Monkey Hypothesis
The idea that primates have a long-standing relationship with alcohol stems from the “drunken monkey hypothesis” proposed by UC Berkeley biologist Robert Dudley. Initially outlined in his 2014 book, The Drunken Monkey: Why We Drink and Abuse Alcohol, the hypothesis suggests that the attraction to alcohol dates back approximately 18 million years to the origins of great apes. Dudley theorized that social communication and food sharing evolved, in part, to facilitate identify fruit sources, including those undergoing fermentation .
Evidence of Fermented Fruit Consumption
For years, skepticism surrounded Dudley’s hypothesis, with many scientists doubting that chimpanzees and other primates actively consumed fermented fruit. But, evidence has been mounting. Researchers have documented chimpanzees sharing fermented African breadfruit, which contains measurable alcohol content .
A 2025 study co-authored by Dudley measured the ethanol content of fruits favored by chimpanzees in the Ivory Coast and Uganda. The findings indicated that chimps consume around 14 grams of alcohol daily, equivalent to a standard alcoholic drink in the U.S. Adjusting for their lower body mass (approximately 40 kilograms compared to a typical human’s 70 kilograms), the researchers estimated that chimps consume nearly two drinks per day .
Urine Analysis Confirms Intake
To further validate these findings, researchers, led by UC Berkeley graduate student Aleksey Maro, collected urine samples from chimpanzees in Uganda. An analysis of 20 samples revealed ethanol byproducts in at least 17, confirming significant alcohol ingestion from fermented fruit .
Collecting the samples proved challenging. Maro, assisted by Sharifah Namaganda of the University of Michigan, developed techniques for gathering urine from leaves and using improvised collection devices to capture samples from beneath feeding trees .
Implications for Human Evolution
These findings suggest that alcohol consumption may have been a regular part of the diet of our human ancestors, potentially influencing our evolutionary history. The availability of ethanol in fruits commonly eaten by chimpanzees indicates that exposure to dietary alcohol was likely commonplace for early primates .