They have shown an understanding of language and a sense of fairness, and now humans’ closest primate cousins have even been found to share a taste for alcohol.
Scientists studying chimpanzees in Guinea have seen evidence of long-term and recurrent ingestion of ethanol by apes.
The 17-year study recorded the animals using leaves to drink fermented palm sap. Some drank enough alcohol to produce “visible signs of inebriation”.
The study - published in the journal Royal Society Open Science - revealed their tipple of choice is naturally fermented palm wine, produced by raffia palm trees.
In the Bossou area of Guinea, where this research took place, some local people harvest “palm wine” from the trees - tapping them at the crown, and gathering the sap in plastic containers, which they collect in the mornings and evenings.
Researchers working in the area had already witnessed chimpanzees climbing the trees - often in groups - and drinking the naturally fermented palm sap.
They used drinking tools called leaf sponges - handfuls of leaves that they chew and crush into absorbent sponges, dip into the liquid and suck out the contents.
To work out the extent of the animals’ indulging, the scientists measured the alcohol content of the wine in the containers and filmed the chimpanzee’s “drinking sessions”.
The research team, led by Dr Kimberley Hockings from Oxford Brookes University and the Centre for Research in Anthropology in Portugal, worked out that the sap was about 3 per cent alcohol by volume. “Some individuals were estimated to have consumed about 85ml of alcohol,” she said, “approximately equal to a bottle of wine”.
“(They) displayed behavioural signs of inebriation, including falling asleep shortly after drinking. On another occasion after drinking palm wine, one adult male chimpanzee seemed particularly restless.
“While other chimpanzees were making and settling into their night nests, he spent an additional hour moving from tree to tree in an agitated manner. Again pure speculation, but it’s certainly something we would like to collect further data on in the future,” the researcher told BBC News.
Alcohol can be toxic, and although there have been unconfirmed anecdotes of non-human primates consuming it in the wild, this is the first time researchers recorded and measured voluntary alcohol consumption in any wild ape.
Dr Catherine Hobaiter from St Andrews University said: “It would be fascinating to investigate the (behaviour) in more detail: do chimps compete over access to the alcohol? Or do those who drank enough to show ‘behavioural signs of inebriation’ have a bit of a slow day in the shade the next morning?”