Researchers working in a Ugandan rainforest report biochemical evidence that wild chimpanzees consume ethanol from fermented fruit, implying that a taste for alcohol could date back to primate ancestors. Last summer UC Berkeley Ph.D. student Aleksey Maro and colleagues collected fresh morning urine from wild chimps to look for alcohol metabolites. To avoid contamination they often caught droplets in plastic bags stretched over forked branches; University of Michigan Ph.D. candidate Sharifah Namaganda, who helped in the field, called that “plastic bag pee” the cleanest sample.
Chimpanzees eat large quantities of fruit—about 10 pounds of pulp per day, including species such as the African star apple—that can ferment as it ripens and produce small amounts of ethanol. Maro suggests that detecting the scent of ethanol might serve as a cue for sugar-rich, calorie-dense foods. Although the amounts chimpanzees obtain are unlikely to produce intoxication, the link between fruit sugars and ethanol could help explain why humans find alcohol appealing.
The team detected ethanol breakdown products in urine from 17 of 19 chimpanzees sampled. At least 10 individuals had metabolite levels comparable to a human who had consumed one or two alcoholic drinks. Maro cautions the study used a limited sample size, but says the results are intriguing and consistent with the idea that ethanol was regularly encountered in ancestral diets.
Published in Biology Letters, the work may prompt new questions about chimp behavior and the evolutionary origins of human alcohol-related practices, says primatologist Cat Hobaiter of the University of St. Andrews, who was not connected to the study. The researchers plan to investigate whether chimpanzees actively prefer fruit containing ethanol. For now, the findings indicate that ethanol has long been present in primate diets and could have played a role in an evolved affinity for alcohol that persists in humans.