For 25 years, University of California, Berkeley biologist Robert Dudley has been intrigued by humans’ love of alcohol. In 2014, he wrote a book proposing that our attraction to booze arose millions of years ago, when our ape and monkey ancestors discovered that the scent of alcohol led them to ripe, fermenting and nutritious fruit.
A new study ( Royal Society Open Science) now supports this idea, which he calls the “drunken monkey” hypothesis.
The study was led by primatologist Christina Campbell of California State University, Northridge (CSUN), and Victoria Weaver who collected fruit eaten and discarded by black-handed spider monkeys (Ateles geoffroyi) in Panama. They found that the alcohol concentration in the fruit was typically between 1% and 2% by volume, a by-product of natural fermentation by yeasts that eat sugar in ripening fruit.
Moreover, the researchers collected urine from these free-ranging monkeys and found that the urine contained secondary metabolites of alcohol. This result shows that the animals were actually utilizing the alcohol for energy — it wasn’t just passing through their bodies.
“For the first time, we have been able to show, without a shadow of a doubt, that wild primates, with no human interference, consume fruit-containing ethanol,” Campbell says in a press release. “This is just one study, and more need to be done, but it looks like there may be some truth to that ‘drunken monkey’ hypothesis — that the proclivity of humans to consume alcohol stems from a deep-rooted affinity of frugivorous (fruit-eating) primates for naturally-occurring ethanol within ripe fruit.”