Wild chimpanzees in Uganda are ingesting quantities of ethanol through their fruit diet comparable to one to two standard drinks in humans. This emerges from urine samples in which high concentrations of ethyl glucuronide (EtG) have been detected, a direct breakdown product of ethanol in the liver. With this, researchers publishing in Biology Letters on 25 February provide the first physiological evidence of substantial alcohol intake by free-living great apes.
In August 2025, the researchers collected twenty urine samples from nineteen individually known chimpanzees in Kibale National Park. The animals were foraging almost exclusively on heavily fruiting Gambeya albida, star apple trees native to Africa. Using field-compatible immunoassays, they tested the urine for EtG, which in humans remains detectable for two to three days after alcohol consumption. Seventeen of the twenty samples exceeded a threshold of 300 nanograms per millilitre; ten of eleven tested samples were even above 500 nanograms per millilitre.
Analysis of 88 fruits from nine trees showed that the fruit flesh contained on average 0.09 per cent ethanol, with peaks of up to 0.40 per cent. Earlier estimates based on fruit consumption put the figure at approximately 14 grams of ethanol per day, roughly 1.4 standard drinks in human terms. The new urine samples now confirm that chimpanzees are genuinely absorbing and metabolising that ethanol.