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10h ago

Wild Chimps Consume About One Drink’s Worth of Ethanol Daily From Fermented Fruit

Published in Science Advances, UC Berkeley’s measurements set a quantitative baseline that lends weight to the “drunken monkey” hypothesis.

Two male chimpanzees eating the plum-like fruit of the evergreen Parinari excelsa tree at Taï National Park in the Ivory Coast in 2021.
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A chimpanzee is seen in the trees of Kibale National Park in Uganda. 

Overview

  • Field teams sampled freshly fallen fruits at Ngogo in Uganda and Taï in Ivory Coast and found average ethanol levels around 0.3% by weight.
  • Based on typical intake of roughly 4.5 kilograms of fruit per day, chimpanzees ingest about 14 grams of ethanol daily, equal to one U.S. standard drink.
  • Adjusting for body size, the dose approximates more than two human drinks per day, yet observers reported no obvious signs of intoxication.
  • Multiple tools verified fruit ethanol content, including a breathalyzer-like device, a portable gas chromatograph, and a chemical assay, with preferred species showing the highest levels.
  • Researchers are collecting urine to test for alcohol metabolites and probing whether chimps selectively seek higher-ethanol fruits, as external experts praise the study for settling debate over ethanol’s prevalence in tropical fruits.