Tipsy Chimps? Study Reveals Wild Apes Consume the Equivalent of Two Drinks a Day

Who thought alcohol would be the one thing that brought us closer to being related to chimps than we thought? A new study suggests that chimpanzees in the wild are consuming the equivalent of several alcoholic drinks each day.

Biologists at the University of California, Berkeley, have discovered that fruit eaten by chimpanzees in Africa often contains measurable levels of ethanol, as the apes are ingesting the equivalent of two alcoholic drinks a day. 

The researchers claim this is the first time such a measurement has been made to determine the ethanol levels in the diets of wild chimpanzees. The results suggest that alcohol is a natural part of their diet and point to potential evolutionary links that offer clues to why humans consume alcohol. 

“Human attraction to alcohol probably arose from this dietary heritage of our common ancestor with chimpanzees,” said UC Berkeley graduate student Aleksey Maro of the Department of Integrative Biology in a statement. “Across all sites, male and female chimpanzees are consuming about 14 grams of pure ethanol per day in their diet, which is the equivalent of one standard American drink.” 

“When you adjust for body mass, because chimps weigh about 40 kilos versus a typical human at 70 kilos, it goes up to nearly two drinks,” adds Maro.  

The Study

The study analyzed 21 species of fruit collected by the ape family in a chimpanzee feeding site in Ngogo, Uganda, and Taï National Park in Côte d’Ivoire. Figs or plum-like drupes are examples of the types of fruits consumed, which showed an alcohol content of 0.26–0.32% by weight. Consuming around 10 pounds (4.5 kilograms) of fruit per day, the average intake of ethanol is around 14 grams per day, which is the equivalent of 1 standard U.S. drink (a standard drink in the United States contains around 14 grams of ethanol, compared to Europe, where the standard is 10 grams).

“The chimps are eating 5 to 10% of their body weight a day in ripe fruit, so even low concentrations yield a high daily total — a substantial dosage of alcohol,” said Robert Dudley, UC Berkeley professor of integrative biology.

“If the chimps are randomly sampling ripe fruit,” he adds, “then that’s going to be their average consumption rate, independent of any preference for ethanol. But if they are preferring riper and/or more sugar-rich fruits, then this is a conservative lower limit for the likely rate of ethanol ingestion.”

Notably, the chimps did not show any signs of intoxication. For the apes to feel the effects of ethanol in their systems, they would have to consume enough fruit that they would display bloating, which suggests they are currently only experiencing low-level exposure.

“Chimpanzees consume a similar amount of alcohol to what we might if we ate fermented food daily,” Maro said. “Human attraction to alcohol probably arose from this dietary heritage of our common ancestor with chimpanzees.”

Vindication For The ‘Drunken Money’ Theory

The recent study builds off of earlier research on Professor Robert Dudley’s “drunken monkey” hypothesis, which suggests that human tastes for alcohol stem from past experiences by our primate ancestors. With the publication of Dudley’s 2014 book, The Drunken Monkey, the idea was initially met with skepticism, but the new findings seem to offer additional support.

The findings also align with additional research studies that show spider monkeys, lemurs, lorises, and even some birds consume or metabolize alcohol from fruit and nectar.

“This dataset has not existed before,” Dudley said. “It points to alcohol consumption as a fundamental feature of fruit-eating animals.”

“For humans, it suggests our relationship with alcohol has a deep evolutionary background.”