Researchers report that wild African chimpanzees are ingesting alcohol from fermented fruit, suggesting a possible evolutionary link to human attraction to alcohol. Aleksey Maro, a Ph.D. student at UC Berkeley, collected chimpanzee urine last summer in a Ugandan rainforest to test for ethanol metabolites. Teams usually gathered samples in the morning when chimps first urinate; one practical technique involved stretching a plastic bag over a forked branch to catch droplets. Field assistant Sharifah Namaganda of the University of Michigan said those uncontaminated bagged samples were the most reliable.
Many fruits eaten by chimpanzees, including the African star apple, can ferment as they ripen and produce ethanol. Maro notes that individuals consume roughly 10 pounds of fruit pulp per day, and the researchers propose that the scent of low concentrations of alcohol could serve as a cue for sugar-rich, calorie-dense foods. That sensory association, they say, might help explain why humans are drawn to alcohol today even when amounts consumed by primates are unlikely to cause intoxication.
Urine analyses detected ethanol in 17 of 19 chimpanzees sampled. For at least 10 animals, measured concentrations were roughly comparable to a human having one or two drinks, though Maro emphasizes the study’s small sample size and cautions against overinterpretation. The findings appear in the journal Biology Letters.
Cat Hobaiter, a primatologist at the University of St. Andrews who was not involved with the work, said the study opens new lines of inquiry into chimpanzee feeding behavior and the possible evolutionary origins of human social practices around alcohol. The research team plans next to test whether chimpanzees preferentially select fruits with fermentation-produced alcohol.