For years, tales of animals intoxicated on fermented fruit were considered rare and humorous coincidences.
However, a recent meta-analysis published in Trends in Ecology & Evolution challenges this view, suggesting that animals that eat fruit and nectar may routinely consume ethanol as a natural part of their diet.
Yeast Begin Fermentation
Kimberley Hockings from the University of Exeter notes, according to WP, that this finding requires a shift from an anthropocentric perspective.
"Ethanol isn’t just something humans use," Hockings says. "It’s far more common in the natural world than previously thought, exposing most animals that eat sugary fruits to some level of ethanol."
The production of ethanol in nature dates back approximately 100 million years, when flowering plants evolved to produce sweet nectar and fruits.
Yeasts discovered these resources and began fermenting them, producing ethanol as a byproduct to ward off bacteria competing for the same sugar-rich foods. Over millions of years, ethanol became a prevalent part of ecosystems.
Today, many animals, especially those with fruit-based diets, encounter fermented food with ethanol levels ranging from about 1–2% by volume, though some tropical fruits have been recorded with alcohol content as high as 10%.
Primates and Birds Among Affected
The study team reviewed over 100 prior studies and concluded that ethanol is more widespread in nature than expected, especially in tropical, humid environments where fruit and nectar are abundant year-round. Ethanol, an indicator of high sugar and energy content, likely attracts animals seeking calorie-rich food sources.
The findings also lend weight to the "drunken monkey hypothesis," which suggests that early primates evolved a taste for ethanol because it indicated high-nutrient foods.
Some animals, like primates and certain bird species, even developed genes that allow efficient ethanol metabolism, potentially helping them adapt to a diet that includes naturally fermented foods.
While scientists still question whether animals actively seek out alcohol, they note that ethanol offers some benefits. It provides a quick energy source, while fermentation aromas help animals locate food. Ethanol may also serve as a natural medicine, as observed in fruit flies that use ethanol-rich environments to protect their eggs from parasites.
The researchers plan to continue exploring how ethanol consumption affects animal behavior, social structures, and cognitive functions, particularly in primates, and whether it influences natural selection in the wild.
