The "drunk monkey" hypothesis.  New discoveries may explain people's vulnerability to alcohol

Why are people attracted to alcohol? Some clues to the evolutionary origin of this tendency can be found in the behavior of some Panama monkeys. According to new research, we may have inherited the attraction to percentages of our ape ancestors, due to primates’ deep preference for ethanol naturally present in ripe fruit.

For 25 years, University of California biologist Robert Dudley has been fascinated by people’s love of alcohol. In 2014, he wrote a book in which he suggested that our attraction to alcoholic beverages began millions of years ago when monkeys discovered that the smell of alcohol indicated ripe, fermented, and nutritious fruits. New research supports what Dudley himself calls the “drunken monkey” hypothesis.

The research was led by the primatologist Professor. Christina Campbell of California State University (CSUN) and her student Victoria Weaver. Researchers collected and discarded fruit eaten by spider mite monkeys (Ateles geoffroyi) in Panama. Scientists found that the alcohol concentration in the fruit ranged between 1 and 2 percent. the sound. Ethanol is formed in them as a result of natural fermentation.

Furthermore, researchers collected monkey urine and found that it contains secondary alcohol metabolites. This result shows that the animals digested the alcohol and used it to produce energy.

“This is the first time we have been able to demonstrate, without a doubt, that wild monkeys, without human intervention, consume fruits containing ethanol,” Campbell says. She said more research is needed, but “it appears that the drunk monkey hypothesis may be correct,” and people’s tendency to consume alcohol is due to the deep craving for the ethanol naturally found in ripe fruit.

A description of the research was published in the Royal Society Open Science Journal (DOI: 10.1098 / rsos.211729).

The ‘drunken monkey’ hypothesis was tested after many years

Dudley presented evidence to support his idea eight years ago in his book Drunken Monkey: Why We Drink and Drink Alcohol. Research has shown that some fruits known to be eaten by primates have a naturally high alcohol content, up to 7 percent. But at the time, Dudley had no evidence that the monkeys specifically searched for and ate the fermented fruit, or that they digested the alcohol it contained.

In a newly reported study, CSUN researchers collaborated with Dudley and University of California, Berkeley alumnus Alexi Maru, to analyze the alcohol content of the fruit. Maru is conducting parallel research on the alcohol content of chimpanzee diets in Uganda and Côte d’Ivoire.

“This study is a test of the ‘drunk monkey’ hypothesis,” explains Dudley, a professor of biology at the University of California, Berkeley. “First, there is ethanol in monkeys’ food, and they eat a lot of fruit. Second, alcohol is metabolized, and secondary metabolites such as ethyl glucuronide and sulfate appear. Ethyl in urine.We still do not know how much alcohol the animals consume and what the possible behavioral and physiological effects are.But we have confirmation of the hypothesis – says the scientist.

The research was conducted in the field on the island of Barrow Colorado in Panama, where Dudley first began to consider the role of ethanol in animal diets and the relationship to our preferences and addiction to alcohol.

Fermented fruit is the basis of the diet

The researchers found that the fruit that black-handed spiders smell and bite into had an alcohol concentration of 1 to 2 percent, or about half the amount found in low-alcohol beer. The harvested ripe fruits were the main component of the monkeys’ diet and came from a tree called the mumpin plum (Spondias Mombin), also known as the jobo tree. For thousands of years, this fruit has been used by the indigenous peoples of Central and South America to produce chicha, a fermented alcoholic beverage.

The researchers also collected urine from six monkeys. Five samples contained ethanol secondary metabolites. “Monkeys probably eat fruit with ethanol because of the calories,” Campbell says. They got more calories from fermented fruit than from non-fermented fruit. She adds that more calories means more energy.

Dudley suspects that monkeys feel the intoxicating effects of alcohol known to humans. “Maybe they don’t get drunk because their intestines fill up before they reach the level of intoxication,” she explains. Eating fermented fruit may have some physiological benefits. Perhaps such foods have an antibacterial effect, and the activity of yeast and microbes may aid in the digestion of the fruit. It can not be ruled out – says the expert.

Dudley Cambell echoed that “human ancestors may also have preferred ethanol-containing fruits for consumption because they contain more calories.” “The psychological and hedonistic effects of ethanol consumption can also lead to increased consumption,” he adds.

Today, alcohol is available in liquid form without the flesh of the fermented fruit filling the intestines, which means that it is easy to overdo it. The idea that a person’s natural predisposition to alcohol is inherited from our ancestors can help us deal with the negative effects of alcohol abuse.

Source: University of California, Berkeley, Photo: Victoria Weaver / CSUN

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