Did you hear the one about the drunken monkey? Primates frequently encounter and consume alcohol in their natural environment, most commonly through fermented fruit. But a study published last year showed that some Chimpanzees are actively seeking it out, and have even developed tools to help them access their preferred tipple!

I’ve written before on the topic of animals and recreational drug use. Research has shown that many animals consume alcohol in their diet, from treeshrews drinking alcoholic nectar in Malaysia to Waxwings (Bombycilla cedrorum) drinking fermented berries of the Brazilian Pepper Tree (Schunus terebinthifolius). But deliberate consumption of alcohol – which is, let’s not forget, a poison – is harder to find.

One thing that all primates seem to share is a special relationship with alcohol. Because most primates evolved on a diet of fruit, they have also evolved to respond positively to alcohol. Fruit loves to turn alcoholic, so primates use evaporated alcohol fumes to sniff out ripe fruits, and alcohol has evolved to become an appetite stimulant. And primates all share a crucial genetic mutation that allows them to process alcohol in the liver – the alcohol dehydrogenase enzyme ADH4. Not only that, but when offered alcohol in captivity, vervet monkeys will choose to consume it, and females seem particularly keen on getting tipsy. But deliberate alcohol consumption in wild primates had never before been reported.

A study published in the Royal Society Open Science last June reported deliberate ethanol consumption by wild Chimpanzees (Pan troglodytes verus) at Bossou in Guinea, West Africa. From 1995 to 2012, when the study ended, the chimps were observed consuming large quantities of the alcoholic drink produced from fermented raffia palm (Raphia hookeri) sap, which measured anywhere from 3.1% ABV to 6.9% ABV!

This behaviour isn’t completely natural, though – local people in Bossou tap the raffia palms, collecting the sap that oozes out in large plastic containers. Here, the natural sugars in Palm sap mean it ferments quickly. What the Chimpanzees have realised is they can use a rudimentary leaf tool to access the fermenting sap inside the plastic container, and have a rather pleasant time. Chimps were observed by the researchers taking leaves, folding them up inside their mouths and using them to scoop or sponge up the raffia-sap moonshine. This allowed them to suck up 10ml shots of the fermented sap, and adults and juveniles alike would manage on average 9 shots a minute!

The authors report that “some of the chimpanzees at Bossou consumed significant quantities of ethanol and displayed behavioural signs of inebriation“. Interestingly, Pentailed treeshrews (Ptilocercus lowii) drink 3.8% ABV nectar on a daily basis, but despite high levels of alcohol in their blood, show no signs of intoxication.

This data shows that Chimpanzees are far from alcohol-averse, and suggests that our last common ancestor may have also enjoyed the occasional tipple, if the opportunity presented.

Want to know more?

• Hockings et al (2015) Tools to tipple: ethanol ingestion by wild chimpanzees using leaf-sponges. Royal Society Open Science
• Wiens et al (2008) Chronic intake of fermented floral nectar by wild treeshrews. PNAS
• Dudley (2004) Ethanol, Fruit Ripening, and the Historical Origins of Human Alcoholism in Primate Frugivory Integrative and Comparative Biology
• Dudley (2000) Evolutionary Origins of Human Alcoholism in Primate Frugivory. Quarterly Review of Biology
• Juarez et al (1993) Voluntary alcohol consumption in vervet monkeys: Individual, sex, and age differences Pharmacology Biochemistry and Behavior