Getting wasted on booze seems like a uniquely human trait, but a study published in Biology Letters found that wild chimpanzees in Uganda are eating fermented fruit, and they’re metabolizing the alcohol.
Urine samples collected in Kibale National Park showed clear traces of ethanol glucuronide, a byproduct of the body’s breakdown of ethanol. Researchers have theorized that chimps were getting a little tipsy after munching on fermented fruits. This new round of research makes it abundantly clear that the alcohol is definitely coursing through their systems.
The idea of monkeys getting drunk is quite cold, pop culturally speaking. Who alive hasn’t seen silly footage of a monkey drinking a beer and some old-timey footage? But scientifically speaking, the “drunken monkey hypothesis” was proposed by biologist Robert Dudley in his aptly titled 2014 book The Drunken Monkey.
His theory argues that primates evolved an attraction to ethanol because it was a ripe, calorie-dense fruit. In tropical forests, sugars naturally ferment as fruit ripens, producing low levels of alcohol. Animals that house several pounds of fruit a day, those tiny little concentrations of alcohol add up.
Urine Tests Suggest Wild Chimps Love Getting Drunk on Nature’s Booze
In the latest round of research, the team analyzed 20 urine samples from 19 western chimpanzees. Seventeen tested above the lower detection threshold for alcoholic metabolites, and nearly half reached levels comparable to what would register in a human after a couple of drinks.
Previous field studies measured ethanol content in fruit consumed by chimps, with some estimating that they contain the equivalent of around a drink a day for a chimp, adjusted for body mass. What was missing was the physiological proof… and now they’ve got it.
Unfortunately, the work required getting a little dirty and gross, namely collecting wild chimp urine left behind in puddles and on leaves, and scooping it up from makeshift plastic-bag contraptions placed beneath trees where chimps fed. Unglamorous work that paid off, as it fills a big gap in a very silly but necessary debate over whether alcohol consumption in primates is incidental or serves some evolutionary purpose.
With that big question answered, researchers can now focus on a series of ancillary questions, like whether chimpanzees actively prefer fruit with higher ethanol content. There are also plenty of questions about how regular exposure affects chimp behavior, social dynamics, and fertility.
For all we know, they are getting drunk at chimp bars in the hope of finding a mate just like us.
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