Scientists studying wild African chimpanzees found evidence that the apes consume ethanol from fermented fruit, suggesting the human attraction to alcohol could trace back to ancestral diets.
Late last summer in the Ugandan rainforest, UC Berkeley Ph.D. student Aleksey Maro and colleagues collected chimpanzee urine to test for alcohol metabolism. The team gathered morning samples—often by catching droplets in a plastic bag stretched over a forked branch—to avoid contamination. Sharifah Namaganda, a University of Michigan Ph.D. candidate who assisted in the field, called such “plastic bag pee” the cleanest sample.
Chimpanzees eat large amounts of fruit—around 10 pounds of pulp per day, including African star apple—which can ferment as it ripens and produce ethanol. Maro notes that smelling alcohol may signal sugar-rich food, a shortcut to calories. While the amounts consumed by chimps aren’t sufficient to cause drunkenness, the association between fruit sugars and ethanol could help explain why humans are drawn to alcohol.
The study found ethanol metabolites in urine from 17 of 19 chimpanzees sampled; at least 10 individuals showed concentrations comparable to a human having one or two drinks. Maro cautions the sample size is small, but says the results are tantalizing: alcohol may have been a regular part of ancestral diets.
Published in Biology Letters, the research could open new avenues for understanding chimp behavior and the evolutionary roots of human rituals and social practices around alcohol, says primatologist Cat Hobaiter of the University of St. Andrews, who was not involved in the study. A next step for the team is to determine whether chimpanzees actively prefer fruits that contain alcohol.
For now, the findings suggest that ethanol has long been present in the diets of our primate relatives and may have contributed to an evolved attraction to alcohol that persists in humans today.
