Chimpanzees regularly consume the equivalent of two alcoholic drinks per day through fermented fruits in the wild, according to researchers at the University of California, Berkeley.
The findings were published in a scientific journal, following an analysis of 21 fruit types commonly eaten by chimpanzees in Uganda and Ivory Coast. The study measured the alcohol content naturally present in these fruits.
Male and female chimpanzees across all study sites were found to consume approximately 14 grams (about half an ounce) of pure ethanol daily through their diet. This is roughly equal to one standard alcoholic drink in the United States. Adjusted for body weight – with chimpanzees averaging 40 kilograms and humans 70 kilograms – this intake corresponds to about two drinks per day for a human.
The team based its findings on zoological research indicating that chimpanzees consume around 10 pounds of fruit daily, which accounts for roughly 75 per cent of their overall diet. The Berkeley researchers estimated the proportion of each fruit type in the average diet to calculate alcohol intake.
Robert Dudley, Professor of Integrative Biology at Berkeley, explained that chimpanzees eat between 5 and 10 per cent of their body weight in ripe fruit every day. Even with low alcohol content in the fruit, this results in a significant daily intake of ethanol.
It remains unclear whether chimpanzees intentionally seek out fruit with higher alcohol content. If they do, actual alcohol consumption may be higher than estimated.
Dudley previously explored this idea in his 2014 book The Drunken Monkey: Why We Drink and Abuse Alcohol. His 'Drunken Monkey Hypothesis' proposes that the shared ancestors of humans and apes likely consumed diets rich in naturally occurring alcohol.
Graduate student Alexey Marov observed that the alcohol intake of chimpanzees is comparable to the amount humans ingest from fermented foods in their daily diets.
In a related study, researchers from the University of Exeter in the UK reported in April that cameras installed in Kantanhés National Park, Guinea-Bissau, captured chimpanzees sharing fermented African breadfruit. The food was later confirmed to contain ethanol.
The footage suggested that the chimpanzees were engaging in alcohol-sharing as a social activity, mirroring human behaviour.
