New research shows that spider monkeys routinely consume fermenting fruit, backing up the notion that humans inherited our proclivity for alcohol from our primate ancestors – the so-called “drunken monkey hypothesis.”
It’s well known that certain non-human primates enjoy a drop of the hard stuff. Chimpanzees are known to raid stocks of palm wine brewed by villagers and feral vervet monkeys in the Caribbean are famous for stealing alcoholic drinks from bars.
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The new study, though, published in Royal Society Open Science, is the first to demonstrate that wild primates – black-handed spider monkeys in Panama – enjoy a tipple as a part of their natural diet, in the form of fermenting mango-like fruits of the jobo tree.
The monkeys’ attraction to alcohol is not for mere amusement. The presence of breakdown products of alcohol in their urine demonstrates that they are gaining a calorific benefit from imbibing it.
Christina Campbell of California State University, who led the work, says it’s not yet known how much alcohol the monkeys are consuming, although it was found to be present in the fruits at concentrations of one to two per cent – comparable to a lager shandy. “We know it’s not enough to make them drunk on a regular basis,” she says.
“In fifteen months, I only saw them get drunk twice. That was towards the end of the fruiting season, when you can smell the alcohol as you enter the forest. They were vomiting and falling out of trees.
“Things that may be beneficial in small amounts can be really bad for you in high quantities,” she adds. “Ethanol is similar to sugar and fat in that respect. It becomes a problem when there’s an excess of it.”
Campbell is concerned that, in their increasingly fragmented habitat, the monkeys may be unable to avoid the fruit when the alcohol content becomes too high. “They don’t have the digestive system to survive on leaves. So if other fruits aren’t available in their forest fragment, they may have no choice.”
Main image: Black-handed spider monkey © Kryssia Campos/Getty