During the last decade, researchers have speculated that our human fondness for alcohol may have been inherited from our ape cousins. This is the so-called “drunk ape” hypothesis. Now a team has confirmed that some people are particularly fond of fermented fruit. Not to get drunk, but because they are higher in calories.
As a child, Robert Dudley lived with an alcoholic father. This motivated him to study the mechanisms of this disease. For 25 years the evolutionary biologist has been asking questions about this subject. In 2014, he came up with the “drunk monkey” hypothesis. This hypothesis states that our cousins and ancestors were particularly attracted to fruits that were naturally fermented and alcoholic. Ripe, nutritious fruits. A hypothesis that now seems to be confirmed by a study conducted in Panama by researchers at the University of California (USA).
The primatologists studied the fruits eaten by black-handed spider monkeys, also known as Ateles geoffroyi. They have found that the fruits favored by these monkeys have an alcohol content resulting from the natural fermentation of sugar under the influence of yeast, ranging from 1% to 2% by volume – some concentrations can be as high as 7%. These fruits are those of the mambú plum tree (Spondias mombin). They form an important part of the diet of black-tailed spider monkeys. And the same fruits have been used for millennia by the indigenous peoples of Central and South America to make chicha, a fermented alcoholic drink.
But even if they smell the fruit before eating it, the researchers don’t think the monkeys are trying to get drunk. They also found that the monkeys’ urine contains secondary metabolites of alcohol — ethyl glucuronide and ethyl sulfate. This proves that the monkeys use this alcohol to produce energy. Fermented fruit is said to contain more calories.
The monkeys probably do not experience the intoxicating effects of alcohol that humans are so fond of. Because they usually have already filled themselves with fruit before intoxication can be felt. Especially since the alcohol content of these fruits is about half that of our low alcohol drinks. “But this gives black-handed spider monkeys physiological benefits,” says Robert Dudley in a statement from the University of California. “Perhaps there is also an antimicrobial benefit in the foods they consume.” It is possible that the activity of yeasts and microbes predigested the fruit.
The researchers think that the choice to put these alcoholic fruits at the center of their diet may have been made by our human ancestors for the same reasons. Because they contain more calories. “The psychoactive and hedonic effects of ethanol can also lead to increased consumption and caloric gain,” says Christina Campbell, the primatologist who led the study.
This phenomenon is even more pronounced today, now that alcohol is readily available in a liquid form that lacks the pulp of the fruit that fills the stomach. The researchers, therefore, assume that alcoholism, like diabetes and obesity, should be considered a diet-related disease.
Un phénomène encore accru aujourd’hui alors que l’alcool est facilement disponible sous forme liquide. Débarrassé de la pulpe des fruits qui remplissent le ventre. Ainsi, supposent les chercheurs, comme le diabète et l’obésité, l’alcoolisme pourrait devoir être considéré comme une maladie liée à l’alimentation.