Why does a glass of wine make a holiday party feel more festive? It might be because our forebears used to party.
Not the ancient Greeks, though they did name a god of wine. Go back even further than that—some 50 million years further, when our primate ancestors began seeking out fermented fruits that naturally contained ethanol, scientists say.
Those that could sniff out ethanol (or alcohol)—which gives off an odor, as we all know from the smell of a beer hall—were rewarded with a tasty nutritional gold mine: plant carbs and calorie-rich ethanol.
All primates can metabolize ethanol, mining it for energy. But research that examined enzymes from ancestral primates indicated that around 10 million years ago, a digestive enzyme mutation allowed African apes—including the common ancestor of humans, gorillas and chimpanzees—to metabolize that alcohol 40 times more efficiently than other primates.
The change made it even more beneficial to be able to find and consume alcohol in the wild, according to Nathaniel Dominy, a professor of anthropology at Dartmouth College.
Fast forward to the advent of agriculture roughly 10 millennia ago, and humans began making alcohol intentionally in large and potent quantities. Today, of course, we have wide access to it.
“It’s been argued that the whole reason we domesticated cereals in the first place was to make beer, not bread,” Dominy said. “Our brains are wired to like it.”
The mismatch of evolutionary wiring and ample availability makes for what Robert Dudley, a professor of integrative biology at the University of California, Berkeley calls “diseases of nutritional excess.” Twenty-five years ago, he developed what he calls the “drunken monkey hypothesis” to explain how we got to our modern alcohol-riddled paradigm.
“Our livers, and our physiology, are sort of like an evolutionary hangover from that time,” Dominy said. “We evolved to be attracted to alcohol, to recognize it in our environment, and then to process it efficiently.”
Scientists have evidence that primates prefer ripe fruits in various African habitats, and that the animals forage for them on the ground. Dominy and his colleagues refer to this “scrumping” behavior in a recent paper.
Scrumping, which can happen in groups, bears some resemblance to human feasting, or perhaps a night out at the pub.
“I spent about 10 of the last 20 years hanging out with wild apes in rainforests in Africa. I have seen them sometimes gather a whole bunch of fruit up, and get a little rowdy,” said Catherine Hobaiter, Dominy’s co-author and a primatologist at the University of St Andrews in Scotland.
Dominy and Dudley say there is no evidence of actual drunkenness, as we would envision it today, in wild primates. Although they occasionally binge-feed, their diets don’t expose them to enough alcohol to cause any obvious impairment.
Dudley and his Berkeley colleague, Aleksey Maro, recently calculated that chimpanzees at sites in Côte d’Ivoire and Uganda consume the equivalent of 1.4 to 1.5 drinks daily, going by an international standard of 10 grams of alcohol in a drink.
On average, these chimpanzees routinely consumed more than one-tenth of their roughly 90-pound body weight in fruit throughout the day—about 10 pounds of ripe fruit containing roughly 14 to 15 grams of alcohol, the researchers found, publishing their findings in a September study in the journal Science Advances.
By body mass, it is equivalent to “a couple glasses of wine over the course of breakfast, lunch and dinner,” Maro said.
Sussing out whether primates prefer fruit with higher levels of alcohol is challenging. So far, much of the data has been collected through observations and analysis of the fruits animals leave behind.
And scrumping behaviors—purposefully seeking out ethanol-heavy, ripened fruit—could be ape- or community-specific, according to Richard Wrangham, an emeritus professor of biological anthropology at Harvard University, who wasn’t involved in the recent papers.
Chimpanzees at a site in Guinea-Bissau in West Africa, according to research led by scientists at the University of Exeter in the U.K., sometimes share the fermented fruits they find—suggesting ethanol shapes apes’ social bonds, much the way it does for humans.
Dominy and Hobaiter posit that abundant fermented fruit on the ground attracts larger groups of apes, which can lead to more schmoozing, but also more jockeying for resources like prey, mates and habitats.
“Alcohol is a fantastic way to lower some inhibitions, and that might mean more time spent hanging out and bonding with each other,” Hobaiter said. “But as a result, chimpanzees may do some slightly more risky behaviors, like patrol the boundaries of their territory or be more likely to pick a fight, as they get bolder—something our species is very familiar with.”
Write to Aylin Woodward at aylin.woodward@wsj.com