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A new study has revealed wild chimpanzees consume the equivalent of multiple cocktails every day due to the ethanol content of fruits they regularly eat. Chimpanzees at the two sites that were studied eat between 5 and 10 percent of their body mass every day in fruit, which means, as researchers have calculated, they consume approximately 14 grams of pure ethanol each day.
Considering the fruit contains an overall concentration of about 0.3 to 0.4 percent alcohol and the fact that chimpanzees are much smaller than humans, it means they are consuming a significant amount of alcohol, on average, every day.
“Across all sites, male and female chimpanzees are consuming about 14 grams of pure ethanol per day in their diet, which is the equivalent to one standard American drink,” said Aleksey Maro, co-author of the study published in the journal Science Advances. “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.”
While it isn’t enough to get the chimpanzees drunk, it does suggest that common ancestors of humans and chimps were exposed to “chronic low-level” amounts of alcohol on a daily basis as well. Maro believes human attraction to alcohol probably arose from this dietary heritage of our common ancestor with chimpanzees.
The drunken monkey hypothesis
“The drunken monkey hypothesis basically says that human attraction to alcohol is due to our ancestral frugivorous [fruit-eating] diet, which is thought to have contained alcohol from fermentation,” Maro told Popular Science.
The theory suggests humans developed an evolutionary preference for ethanol because it could have “helped us locate sugar calories from a long distance, and possibly because during periodic bottlenecks in food availability, fermentation could have unlocked nutrients that would otherwise would have remained chemically inaccessible.”
Robert Dudley, UC Berkeley professor of integrative biology and senior author of the research paper, has been studying this hypothesis for more than 20 years. He even wrote a book about it in 2014 titled The Drunken Monkey: Why We Drink and Abuse Alcohol.
He said that one theory about why animals seek out ethanol is that its odor helps animals find food with a higher sugar content, providing greater energy returns over time. Alcohol also may increase the pleasure of eating, similar to sipping wine with dinner. It’s also possible that sharing alcohol-infused fruit plays a role in social bonding among primates or other animals.
“It just points to the need for additional federal funding for research into alcohol attraction and abuse by modern humans. It likely has a deep evolutionary background,” Dudley said.