A new study confirms the controversial "drunken monkey" hypothesis, which posits that wild chimpanzees regularly consume alcohol. Scientists detected traces of ethanol in the urine of primates living in the forests of West Africa. The alcohol levels were comparable to those causing intoxication in humans, indicating a deliberate search for fermented fruits. The discovery sheds new light on the evolutionary history of human alcohol consumption.

Confirmation of the Drunken Monkey Hypothesis

The study detected ethanol metabolites in chimpanzee urine, providing the first direct evidence of alcohol consumption by primates in the wild.

Alcohol from Fermenting Pulp

The source of alcohol is fermented raffia palm fruits, from which the monkeys consume sap. The fermentation process occurs naturally due to yeast.

Dose Comparable to Intoxication

The estimated blood alcohol level in chimpanzees corresponds to a dose of 1-2 drinks per day for a human, which can lead to noticeable behavioral effects.

Evolutionary Roots of Alcohol Consumption

The discovery supports the theory that the ability to metabolize alcohol evolved in the common ancestor of humans and apes as an adaptation to a diet containing fermenting matter.

An international team of scientists has obtained the first direct evidence that wild chimpanzees deliberately consume alcohol. The study, published on February 25, 2026, confirms the long-debated drunken monkey hypothesis. Researchers analyzed urine samples collected from a chimpanzee community in Taï National Park in Côte d'Ivoire. The detected ethanol metabolites clearly indicate that the monkeys drank fermenting sap from raffia palm fruits.

The process is entirely natural. Chimpanzees use leaves as "tools" to drink sap collected in hollow trunks. This sap ferments due to wild yeast, reaching an alcohol concentration of up to 6.9%. Sample analysis showed that the animals consumed alcohol in amounts equivalent to 1-2 drinks per day for a human. „This clearly shows that the Taï chimpanzees regularly consume alcoholic beverages.” — Kimberley Hockings Scientists also observed changes in the animals' behavior after consumption, including reduced activity and increased sleep, suggesting noticeable intoxication effects.

The common ancestor of humans and chimpanzees lived in Africa approximately 6-8 million years ago. The evolution of the alcohol dehydrogenase enzyme (ADH4), responsible for breaking down ethanol, in this ancestor may have been a key adaptation to a diet containing fermented fruits, providing access to additional calories. The discovery is significant for understanding the evolution of human alcohol-related behaviors. It suggests that a predisposition to consuming psychoactive substances has deep evolutionary roots and is not solely a product of modern culture. The next step in the research will be to determine whether the monkeys prefer fermented sap or treat it as a substitute when fresh fruit is unavailable.

Mentioned People

  • Kimberley Hockings — Scientist, co-author of the study confirming chimpanzee alcohol consumption.