The Professor at Large – The Drunk Monkey Hypothesis

IThis is not a new hangover cure, but a serious study that has stirred up the oenological world. Researchers at the University of California studied the population of Ateles geoffroyi, Geoffroy’s Atèles (after French naturalist Étienne Geoffroy Saint-Hilaire). These are black-armed spider monkeys and those that interest us live in Panama, on the island of Barro Colorado. These primates eat mombins, a cross between a plum and a lemon. The trick is that some of these mombins are so ripe that they start to ferment a little.

The scientists observed the animals for twelve hours, from 6 am to 6 pm. The alcohol content of most fruits consumed ranged from 1% to 2%. It appears that spider monkeys prefer these lightly fermented fruits to less alcoholic ones. Here is the researchers’ conclusion:

“This study shows that spider monkeys on Barro Colorado Island consume low levels of natural ethanol as part of one of their wild foods, and this is the first such demonstration for a fruit-eating primate. »

This work revived the drunken monkey hypothesis put forward earlier in the century by Robert Dudley, also of the University of California.

What is it about ? As I explain in my book Why do we drink wine? (Duneau), the idea is this. In the Paleolithic, before settled life and the development of agriculture, hunter-gatherers ate fruits. In search of fruits, they preferred those that had begun fermentation.

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Indeed, the ethanol molecule had a positive effect on several levels. First, couples can help fruit lovers find ripe berries. Back then, ethanol was a great indicator of ripeness, much better than skin color or thickness. In addition, it acted as an appetite stimulant and, as a final reward, contained more kilocalories than sugar.

Natural selection

Behavioral response to ethanol, that is, the fact that fruit is very ripe and therefore contains little alcohol, may have acted as a form of natural selection for our hominin ancestors. One way or another, we would be their worthy descendants. If one day we were summoned to the Supreme Court and asked: “Why did you drink?” we would have to cite family history as a mitigating circumstance.

In truth, studies other than that of Geoffroy’s spider monkey have already supported the drunk monkey hypothesis with alcohol levels over 1% or 2%. Simply put, we have already found primates who liked a glass of moonshine.

Take, for example, a study by Kimberly J. Hawkings, an anthropologist based in Portugal. He and his colleagues observed the chimpanzee community in Bossu, Guinea between 1995 and 2012. Members of the community ingested up to a liter of fermented juice per day, which ranged in alcohol content from 3.1% to 6.9%. Chimpanzees even make something like a vessel out of the leaves to pump out the precious nectar. The trick is that the palm sap was cut by local pickers. When the natives bleed the palm trees too close to where the chimpanzees live, the latter suck the cat out of them.

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However, the best study on this topic that I have highlighted in my book remains that of Ptilocercus lowii, or Löw’s Ptilocercus, by a German group. It is a scandent, the only species of the genus Ptilocercus. This small placental animal, which lives in the tropical forests of Malaysia, measures about thirteen centimeters and weighs from forty to sixty-two grams. Its lifestyle is arboreal and its very long and bushy tail can reach twenty centimeters.

The teams demonstrated that Ptilocercus lowii feeds on palm nectar, which is fermented by natural yeasts. The maximum alcohol content can reach 3.8%. The story is compounded by the fact that doses ingested by our fragile little animals would have an effect on a nightclub bouncer, while Ptilocercus shows no signs of intoxication.

Here the question arises: what is the relationship between Ptilocercus and monkeys? We must talk about monkeys if we want to demonstrate or support the drunken “monkey” hypothesis. In truth, these small shrews have been identified by American researchers as the closest relatives of primates, an order that includes, among other things, small apes and large anthropoids, including hominids, of which Homo sapiens is a part.

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