Chimps drink a daily lager-equivalent from ripe fruit, study finds

A new study finds wild chimpanzees in Côte d’Ivoire and Uganda ingest the equivalent of about a bottle of lager in ethanol each day by eating ripened fruit, according to researchers. Based on observed fruit consumption, the chimps are estimated to ingest roughly 14 grams of ethanol daily — about 330 milliliters of lager or nearly two UK units. The discovery provides new data on how primates use fermented fruit as a food source and how such behavior might relate to human attraction to alcohol.

The research team measured ethanol content in fruits that chimpanzees routinely eat, including figs and plums, in wild populations. They then estimated daily intake from the typical amount of fruit consumed. The fruits most commonly eaten were those with higher alcohol content, which helped push the overall figure toward the 14-gram mark. The analysis drew on field observations from chimpanzee groups in both Côte d’Ivoire and Uganda. [Image: Chimps foraging for ripe fruit.]

The findings bolster the so-called "drunken monkey" hypothesis, which argues that humans may have inherited a taste for alcohol from a common primate ancestor that relied on fermented fruit as a sugar source. The idea was first proposed by Aleksey Maro of the University of California, Berkeley, who is a co-researcher on the study. "Human attraction to alcohol probably arose from this dietary heritage of our common ancestor with chimpanzees," Maro said. While the concept faced early skepticism, researchers note that more observations of primates foraging on fallen, fermenting fruit have accumulated in recent years.

What we're realising from this work is that our relationship with alcohol goes deep back into evolutionary time, probably about 30 million years," said Catherine Hobaiter, a primatologist at the University of St Andrews who was not part of the research team. Her comments reflect a growing view that social and ecological contexts of fruit foraging may have shaped early primate interactions with alcohol and one another on the forest floor.

But other experts caution against overstating the implications. Kimberley Hockings, who studies primates at the University of Exeter and was not involved in the study, emphasized that the chimpanzees observed did not reach levels of intoxication. Had the animals become drunk, she said, it would likely not have improved their survival chances. The study’s authors also stress that chimpanzees face significant conservation challenges. According to the International Union for Conservation of Nature, chimpanzees are endangered, with habitat loss from farming, logging, and road-building among the top threats to their populations.

The study advances the conversation about how long humans have shared a relationship with alcohol and how primate diets can illuminate aspects of our own evolution. Published in Science Advances, it anchors a broader narrative about the deep, evolutionary roots of alcohol preference and the role of fermented fruit in primate and human history.

Beyond academic interest, the research underscores the importance of conserving chimpanzee habitats to protect behavioral and ecological diversity that may hold clues to human evolution. As forests continue to change across Africa, understanding these dietary patterns helps scientists interpret how primates adapt to shifting food sources — insights that may also inform how we think about conservation strategies in a changing climate.