KAMPALA — A new study suggests that chimpanzees, our closest living relatives, may consume the equivalent of about one alcoholic drink per day by eating fermented fruit, a finding that could offer new insights into the evolutionary roots of human alcohol consumption.
The study, published in the journal Science Advances, is the first to quantify the amount of alcohol wild chimpanzees consume. While researchers have long suspected that apes ingest alcohol, this report provides a concrete estimate based on fieldwork in Uganda and Ivory Coast.
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The Drunken Monkey Hypothesis
Researchers observed two groups of chimpanzees and analyzed the fruit they ate, estimating that the animals consume about 14 grams (0.5 ounces) of ethanol per day. This is roughly the equivalent of 1.4 alcoholic drinks. When adjusted for their smaller body weight, the dosage is comparable to a human drinking 2.6 alcoholic beverages a day.
“The chimps are eating 5 to 10% of their body weight a day in ripe fruit, so even low concentrations yield … a substantial dosage of alcohol,” said senior study author Robert Dudley, a professor at the University of California, Berkeley, in a news release.
Dudley is known for coining the “drunken monkey” hypothesis, which posits that the human desire for alcohol is linked to our ancient primate tendency to seek out and consume ripe, sugar-rich, and alcohol-containing fruits.
Field Research and Findings
The research team, which included scientists from American and Ivorian universities, collected and tested ripe fruit from 20 species in both Uganda and Ivory Coast. They found that the fruit contained an average of 0.31% to 0.32% ethanol. Given that the chimpanzees typically ate around 4.5 kilograms (10 pounds) of fruit per day, their daily ethanol intake was approximately 14 grams.
The study found that the most commonly eaten fruits at each site—a type of fig in Uganda and a plumlike fruit in Ivory Coast—had the highest alcohol content. This indicates that the chimpanzees may be selectively consuming riper fruits with more fermented sugar.
Despite this intake, experts believe the chimpanzees are “unlikely” to get drunk, as they consume the fruit throughout the day. Kimberley Hockings, an associate professor at the University of Exeter who was not involved in the study, said the data shows ethanol is not a deterrent to chimpanzee feeding but does not confirm it is an attractant.
Dudley hopes the findings will draw more attention to the deep evolutionary background of alcohol consumption. “It just points to the need for additional federal funding for research into alcohol attraction and abuse by modern humans,” he said.
