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2d ago

Wild Chimpanzees Consume Human-Equivalent of Two Drinks a Day From Fermented Fruit

Field measurements at two African sites deliver the first estimate of routine ethanol exposure in wild chimps, bolstering an evolutionary hypothesis about alcohol attraction.

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

  • Scientists measured alcohol in 21 fruit species eaten by chimps at Ngogo, Uganda, and Taï, Ivory Coast, finding average ethanol levels around 0.3% by weight.
  • Based on established intake of roughly 4.5 kg of fruit per day, chimps ingest about 14 grams of ethanol daily—about one U.S. standard drink, or two when adjusted for body mass.
  • Researchers tested freshly fallen, undamaged fruit using multiple methods, including a breathalyzer-like device, a portable gas chromatograph, and a chemical assay.
  • Chimpanzees showed no obvious signs of intoxication during normal foraging, and true drunkenness would likely require binge eating to the point of stomach bloating.
  • The results support the ‘drunken monkey’ hypothesis, and the team is now analyzing urine for alcohol metabolites to confirm exposure and probe any preference for higher-ethanol fruits.