Previous research has shown that when captive aye-ayes and slow lorises were offered nectar with varying percentages of alcohol, they finished off nectar with the highest alcohol content first.
Missing link to human drinking
While there is little to indicate that chimps are getting drunk from the fruit, experts say it could explain why humans have developed such a fondness for alcohol.
The common ancestors of humans and chimps were likely also exposed daily to alcohol from fermenting fruit.
Chimps and humans share the same enzyme that helps them to process alcohol.Credit: LaPresse
“Chimpanzees consume a similar amount of alcohol to what we might if we ate fermented food daily,” said UC Berkeley graduate student Aleksey Maro of the Department of Integrative Biology.
“Across all sites, male and female chimpanzees are consuming about 14 grams of pure ethanol per day in their diet, which is the equivalent to one standard American drink (slightly more than the standard Australian measure of 10 grams).
“When you adjust for body mass because chimps weigh about 40 kilos versus a typical human at 70 kilos, it goes up to nearly two drinks.
“Human attraction to alcohol probably arose from this dietary heritage of our common ancestor with chimpanzees.”
The ‘drunken monkey’ hypothesis
Previous studies of the human genome have shown that the ability to process alcohol dates from about 10 million years ago, about the same time when our ancestors were moving from the trees to the ground.
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Great apes, such as chimps, who shared an ancestor with humans between eight and 10 million years ago, also possess the same enzyme – alcohol dehydrogenase – which helps them efficiently break down ethanol, like humans.
More than 10 years ago, Professor Dudley first suggested humans inherited their appetite for alcohol from primate ancestors who ate fermented fruit from the forest floor, a theory dubbed “the drunken monkey hypothesis”.
At the time, many scientists were sceptical, claiming that primates avoided ethanol in fruit.
But in recent years, several studies have shown apes do like fermented food, and may have evolved the ability to metabolise ethanol to allow them to eat windfall fruit that monkeys and other animals struggle to digest.
Professor Dudley believes apes may seek out the smell of ethanol because it signals that a fruit has a higher sugar content and will be more enjoyable to eat.
The most frequently consumed fruits at each site, a fig in Nigeria and the plum-like fruit of the evergreen Parinari excelsa in Ivory Coast, were found to have the highest alcohol content.
The new study was published in Science Advances.
The Telegraph, London
