Not only would chimpanzees cook if they could, but they might go for a postprandial libation, as well.
In a study published Thursday by the Royal Society, chimps in Bossou in the Nzérékoré Region of southeast Guinea have been observed regularly consuming alcohol from the raffia palm. Its sap is collected in containers hung from the trees by local villagers, where it naturally ferments. Over 17 years, the chimps have learned to drink the palm wine by dunking an absorbent leaf in the brew and then sucking the booze down.
And the palm hooch isn’t for lightweights. It’s between 3.1 percent and 6.9 percent ethanol by volume, about the same as your average pint of beer. Researchers estimated that some chimps ingested as much as 84.9 ml of ethanol in any given drinking event, which is about the same as three and a half Budweisers.
“Some of the chimpanzees at Bossou consumed significant quantities of ethanol and displayed behavioural signs of inebriation,” the study reports. “Researchers rarely collected detailed behavioural data before versus after exposure to ethanol, but some drinkers rested directly after imbibing fermented sap.”
Susana Carvalho, a postdoctoral researcher at George Washington University and a co-author of the study, told The Daily Beast that others behaved more roughly.
“I have also seen an individual that was acting a bit more restless than the rest of the group” after ingesting a lot of palm wine, she said. “The sort of behavior that we see in humans seems to be close to what we observe [in the wild]. You drink too much and you want to sleep; or you drink too much and you get kind of restless.”
Over 17 years of observation, multiple researchers witnessed chimps boozing it up 51 times, suggesting the consumption of alcohol is not accidental. (Given that it’s found in plastic containers and the chimps have to construct a leafy tool to drink it, that seems obvious.)
“We observed individuals repeatedly consuming fermented palm sap—often in large quantities—suggesting that accidental ethanol ingestion is unlikely,” the study notes.
Still, cocktail hour among the chimps isn’t a common event. (One male accounted for 14 of the 51 drinking events.) But among the Bossou chimps, it was without direct human interaction and habitual enough for researchers to deem it voluntary, making chimps one of the few animals other than humans that seek out alcohol to take the edge off after a hard day in the jungle.
(Chimps aren’t even the only primate with a taste for tipple. Monkeys on St. Kitts are known to steal tourists’ cocktails, but it’s not clear if they’re deliberately seeking out alcohol or if they’re just reacting to humans.)
The research adds to the “drunken monkey hypothesis” of human evolution, which posits that the last common ancestor of modern great apes and humans, as a fruit-eating animal, gained an evolutionary advantage by “learning to associate the smell and taste of alcohol with ripe fruit,” according to Robert Dudley, a researcher at the University of California and the author of The Drunken Monkey: Why We Drink and Abuse Alcohol. Only humans and other great apes can effectively metabolize alcohol, the result of a genetic mutation that happened some 10 million years ago. It allows people and chimps to ingest relatively large amounts of alcohol and not poison themselves to death.
The evolutionary advantage of the ability to metabolize ethanol also stimulates the appetite, increasing the drive to hunt for food and thus upping calorie intake.
The research also adds to the data on our ancestors’ diets and when the common ancestor started spending more time on the ground, which researchers speculate spurred the use of tools. Even today, Carvalho said, chimps spend a lot of time on the ground and they’re known tool users, including stone tools.
“Terrestriality has been linked to the origins of tool use,” she said. “And chimpanzees are known to be tool users par excellence in all of the animals that use tools, other than humans.”
With that tool use, along with the fondness for the bottle (or leaf, in this case), complex social structures, language, self-awareness, and an appreciation of cooked food, it would seem the differences between chimps and humans are shrinking every day.