[Un article de The Conversation écrit par Mickael Naassila – Professeur de physiologie, Directeur du Groupe de Recherche sur l”Alcool & les Pharmacodépendances GRAP – INSERM UMR 1247, Université de Picardie Jules Verne (UPJV)]
Fruits too ripe on the ground, slightly swollen, slightly soft, fragrant … and slightly alcoholic. This is what our ancestors of the line of hominoids, today represented by the great apes and the human, often found in the tropical forests of Africa. And this little taste of ethanol, they loved it.
According to the hypothesis of “Drunken Monkey” (drunk monkey), formulated by Robert Dudley in 2000, the consumption of ethanol in humans would not come from a modern cultural degeneration, but from an ancient evolutionary pressure. Millions of years before man invented agriculture and fermentation, our frugivore ancestors have already been lovers of naturally fermented fruit. And the passage from the treetops to the ground with the gleaning of fruit fallen to the ground would have accelerated this evolution.
A mutation that changes everything
A study published in 2014 reports that around 10 million years ago, a mutation in the enzyme ADH4 (alcohol-ethodrisenase) allowed our ancestors to metabolize ethanol 40 times more effectively. This adaptation occurred precisely among our ancestors of the line of hominoids (common ancestor of humans, chimpanzees and gorillas but not among orangutans).
For what ? Because they lived in the heights of trees, where fruits do not ferment as much as on the ground. The ancestors of the chimpanzees and gorillas, they were gladly descended glean the fallen fruits, more likely to have fermented under the natural action of the yeasts. Having access to many fermented fruits while being able to degrade alcohol then became an evolutionary advantage, this mutation thus becoming a “function gain” allowing to find more easily food rich in calories.
In the same way that the mutation of the ADH allowed primates to adapt to improve their diet, the human being has also adapted more recently with mutations of the other enzyme, the ALDH, which degrades acetaldehyde (toxic degradation product inducing a reaction of intolerance to alcohol with facial redness (a “flush”), tachycardia) toxic). This alcohol intolerance reaction would be supposed to protect us from alcohol consumption, a molecule which with its equally toxic metabolite can cause severe damage to our health.
Ethanol as an olfactory treasure card
Ethanol emitted by fermented fruits does not only feel closely. It diffuses remotely and was probably used as an olfactory signal to primates to locate energy resources rich in sugar.
Ethanol is largely present in nature, mainly by the fermentation of fruit sugars by yeasts. A study reported the concentrations of alcohol of different fruits not yet fallen to the ground but some of which were too ripe. The concentration varies according to species and environments: traces (0.02–0.9 %) were measured in temperate and subtropical fruits such as the Sorbier, the Sycomore fig tree or the date palm, while in wet tropical areas, particularly favorable to fermentation, much higher contents (up to 10 % in certain palm fruits) were observed in the Panama) Fruits too ripe. Although most fruits have low levels (<0.2 % on average), their repeated consumption can represent a significant source of ethanol for frugivore animals. This natural alcohol production is part of a complex relationship between plants, yeasts and animals: fruits offer sugars, yeasts colonize and ferment, and attracted animals help disperse both seeds and yeast spores, suggesting a form of "ecological mutualism".
Many anecdotes circulate on “drunk” animals after consuming fermented fruits … Elephants and baboons in Africa with Marula, or even an impulse in Sweden stuck in a tree after eating fermented apples. However, these stories rarely remain scientifically validated: neither the ethanol content of the fruit, nor the presence of alcohol or his metabolites in animals have been measured. On the other hand, we know that some mammals, such as green monkeys introduced to the Caribbean, do not hesitate to steal and consume cocktails of alcoholic fruits left unattended by tourists on the beaches of St Kitts.
A study reports that bossou chimpanzees in Guinea use wrapped leaves like “sponges” to drink fermented palm sap containing up to 6 % ethanol.
And it is not a hiding picole: they drink in a group, the leaves happen, almost like a community aperitif. What revisit our ideas on alcohol and social bond. The gleaning activity of fermented fruits on the ground and alcoholic then becomes a social motivation, already! We didn't invent anything.
Nowadays, alcohol flows to waves, but our enzymes have not followed
The evolution gave us a liver capable of degrading about 7 g of ethanol per hour. It is not much faced with modern cocktails. In the past, the volume of ethanol ingested was naturally limited by what contained … a monkey stomach filled with fruit. Today, we can drink dozens of grams in a few sips of highly alcoholic drinks. A shot (a “baby”) of whiskey or spirits at 40 ° and only 3cl contains 10g of alcohol!
It is therefore not surprising that we had to face the problem of excessive consumption of alcohol and alcohol addiction which have heavy consequences on health and our societies. We speak of “Mismatch” and “Wood Gueule linked to evolution”. The mutations in our genes coding ADH and ALDH have not yet allowed our species to deal with the harmful consequences of excessive alcoholism.
To conclude, our instinct of drinking is old, but the risks are new.
Our alcohol attraction is not a modern anomaly. It is an evolutionary heritage, a bug of the era of humid forests, where ethanol meant calories and survival. But in a world where alcohols are concentrated, accessible, omnipresent … which was an advantage has become a risk factor for our health and a priority public health issue.
With an unwavering passion for local news, Christopher leads our editorial team with integrity and dedication. With over 20 years’ experience, he is the backbone of Wouldsayso, ensuring that we stay true to our mission to inform.
