Chimpanzees consume the equivalent of two human alcoholic drinks each day thanks to their fondness for ripe fruit, researchers have said.
Wild chimpanzees regularly eat around 10% of their body weight in ripe fruit daily, and because the fruit often is undergoing natural fermentation – the process that turns sugar into alcohol – it means the apes are consuming the human equivalent of two cocktails daily.
A team from the University of California, Berkeley, measured the alcohol content of the fermented ripe fruits consumed regularly by chimps at two sites – in Uganda and Ivory Coast.
They estimated that, based on their usual food intake, the animals may ingest 14g of ethanol, the principal type of alcohol found in alcoholic drinks, every day.
A standard alcoholic drink in the US contains about the same amount of alcohol – 14g.
When the relative body weights of humans and chimps are factored in, the apes have roughly the equivalent of two standard alcoholic drinks.
The chimps showed no obvious signs of being intoxicated, the scientists said, as they ate the fruit over many hours during foraging, limiting the alcohol’s impact.
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Lead author Aleksey Maro, from Berkeley’s Department of Integrative Biology, said it’s “difficult to say how much consuming this amount of dietary alcohol would affect the behaviour of chimpanzees.
“We know that just the presence of a lot of ripe fruit can affect things like how often they go on territorial patrols and
hunts.
“And the oestrous cycle of female chimpanzees, when they are fertile, is timed around when large amounts of food are available.
“It’s possible ethanol could play a role in some of these diet-related dynamics, especially when they’re able to consume large volumes of fruit quickly.”
Chimpanzees are specialists in consuming ripe fruits, which represent more than 70% of their diet.
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Researchers, whose findings were published on Wednesday in the journal Science Advances, tried 21 fruit species at the two study sites – Uganda’s Kibale National Park and Tai National Park in Ivory Coast.
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Mr Maro described the number and diversity of fruit species in the chimpanzee diet as “staggering”, ranging from “bowling ball-sized fruits to fruits that are composed almost entirely of seeds with just a little pulp glued to them – and everything in between”.
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The team studied those species most popular with the chimpanzees, which in Uganda were figs, while those in Ivory Coast preferred a plum-like fruit with bright green flesh.
Mr Maro said “it’s certainly plausible” that the chimps actively look for fruit with higher alcohol content – riper fruit with more sugars to ferment.
“We hypothesise that they judge whether to eat a fruit in their hand partly based on the smell of ethanol.”
