Many love to have a glass of wine with dinner. Some prefer beer after work, others — whiskey, vodka, or cognac on occasion (and sometimes without). But where does this human craving for alcohol come from? Why has ethyl alcohol, which is essentially a toxin, that is, a poison, become an integral part of human culture?
The answer, scientists claim, lies in the diet of our ancestors. Moreover, very distant ancestors. An international group of biologists has presented new evidence for the so-called Drunken Monkey Hypothesis. It states that humans' attraction to alcohol is explained by the fact that we are descendants of primates that regularly consumed fermented fruits. And even specifically sought out overripe fruits.
Ethanol serves as a signal
The idea that monkeys are quite the alcoholics emerged a quarter of a century ago. In 2000, biologist Robert Dudley from the University of California, Berkeley, suggested that the attraction to alcohol, before becoming a bad habit passed on to Homo Sapiens, was a kind of evolutionary "bonus," an advantage over competitors for a place in the sun.
The essence is simple: a fruit that has slightly fermented contains more calories. It is sweeter and more nutritious. Therefore, it is better to eat it than just a ripe fruit (and even more so — an unripe one). Ethanol, arising from sugar during fermentation, emits a strong smell and serves as a signal for animals: this fruit is ripe — pick it, eat it, and gain energy!
For a long time, this was just a hypothesis. The first attempts to prove it were made in 2022 when scientists studied the behavior of spider monkeys (the Geoffroy's tamarin species) in Panama. At that time, metabolites of ethanol were found in their urine for the first time, indicating that alcohol is regularly consumed by primates and absorbed by their bodies.
"It seems that there may be some truth in the Drunken Monkey Hypothesis," said the biologists.
A shot of vodka in the morning
The continuation followed in 2025. Researchers went to Kibale National Park in Uganda to observe chimpanzees. For 11 days, scientists monitored how the primates consumed the fruits of the tropical tree Gambeya albida, known as star apple.
The results exceeded expectations. Urine analyses of wild chimpanzees showed that 17 out of 19 samples contained ethyl glucuronide — a direct breakdown product of ethanol. Moreover, in ten cases, the concentration of metabolites exceeded the threshold value — 500 nanograms per milliliter.
For humans, this level is equivalent to the state after consuming one or two standard servings of alcohol (for example, a shot of vodka or a glass of beer) in the last 24 hours. Chimpanzees reached such levels by midday after gorging on fallen fruits in the morning.
"They were literally gorging on sweet fruits," the authors of the study published in Biology Letters write. "We suspect that the animals may have climbed higher into the tree canopies, selecting the ripest and most fermented fruits there."
There may be other benefits
Interestingly, the alcohol concentration in star apple fruits turned out to be not that high, at least lower than the average in other tropical fruits. The secret lies in the quantity: monkeys eat a lot and for a long time, ensuring a constant low-dose "background." According to scientists' estimates, an adult chimpanzee can consume up to 4.5 kg of such fruits in a day.
But let's think: if a person drinks one and a half liters of beer in the morning, he is unlikely to be able to deftly swing through the vines. So why do the monkeys being observed by researchers (for example, in the same national park in Uganda) not appear to be intoxicated?
First, the doses are still not the same as those found in strong alcohol. The fruits consumed by the animals contained only 1–2% alcohol. Secondly, and this is a key point of the hypothesis, over millions of years of evolution, primates have developed a resistance to ethanol — a mechanism for its breakdown has emerged, and in some individuals, it works quite quickly. Humans, chimpanzees, bonobos, and gorillas share a common mutation in the gene responsible for processing alcohol that enters the body. And this mutation allows us to metabolize alcohol 40 times more efficiently than, say, many other mammals. Thus, evolutionarily, we have long adapted to a "friendship" with ethanol.
That very biologist Robert Dudley, whose Drunken Monkey Hypothesis from 25 years ago has finally received confirmation, notes that, in addition to calorie consumption, the attraction of monkeys to fermented fruits may have other benefits. For example, ethanol can have an antimicrobial effect, providing physiological benefits to the body.
Harmful inheritance
However, scientists have one important question left that prevents them from concluding the Drunken Monkey Hypothesis. Yes, primates eat fermented fruits. Yes, alcohol is absorbed in their bodies. But there is still no strict evidence that they intentionally seek out fruits with a higher ethanol content. Perhaps they are simply interested in sugar, and alcohol is just a byproduct? And they do not strive for intoxication at all.
"The results support the hypothesis, but only partially," the authors of the study cautiously conclude. "We do not know whether they choose fruits by the smell of alcohol or simply by sweetness."
The next expedition to Uganda, planned for the near future, should answer the questions: does alcohol influence the gastronomic preferences of primates, and how does regular ethanol consumption affect their behavior and health in the long term?
One way or another, it all seems like the love for alcoholic beverages is embedded in us, humans, at a genetic level. Our ancestors simply sought energy for survival in fermented fruits, while we look for a way to relax after work or another stress in alcohol.
But evolution, as it often happens, played a cruel joke on Homo Sapiens: what helped survive in the jungle has become a cause of addiction in the modern world. So, with all due respect to science, it is not worth testing your "monkey inheritance" for strength. Remember that excessive alcohol consumption is harmful to your health.
