A chimpanzee might not walk into a bar, but these apes have a taste for alcohol.
Specifically, they consume alcohol inside fermented fruits, from figs to star apples to local stone fruits. As these fruits ripen, they produce sugars, which combine with yeast to produce ethanol. While the amount of ethanol in an individual piece of fruit is very small, chimps are voracious, with some eating about 4.5 kilograms of fruit a day. Old research suggested that, adjusted for body weight, a chimpanzee might ingest the equivalent of more than two standard alcoholic drinks a day. But proof of this consumption had been elusive—until now.
A new analysis of chimpanzees’ pee confirms that the apes ingest enough alcohol to show up on field tests of their urine. The finding could shed light on how the psychoactive substance affects the animals’ behavior.
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“We can’t jump the gun on the conclusions, but there are a lot of avenues where the psychoactive influence of alcohol would be useful for chimpanzee behavior and ecology,” says Aleksey Maro, a doctoral researcher at the University of California, Berkeley, and lead author of the study.
Maro and his team followed a group of chimps at Ngogo, a research site within Uganda’s Kibale National Park. They collected the apes’ urine and identified the presence of alcohol in the samples on-site with dipstick assays that are typically used to test humans for alcohol consumption.
We know that alcohol can significantly influence human behavior, whether by impairing our cognition or affecting our motor function—not to mention by causing hangovers. But it’s possible that consuming alcohol could proffer some benefit to chimps, for example, by lowering their anxiety while they guard their territory or by boosting socialization within their group.
Some researchers doubt that chimps seek out these effects the way humans might pursue a little light relief at a bar—and it’s unclear if chimps feel alcohol’s effects in the same way we do.
“In a sense, alcohol makes humans more like chimpanzees,” says Kevin Langergraber, a chimp ecologist at Arizona State University, who was not involved in the study. “I have been at Ngogo many times when the chimpanzees are feeding on these supercrops of Chrysophyllum fruits and have never noticed that the chimps are behaving strangely.”
Maro says a better way to think about the chimpanzees’ alcohol ingestion is to compare it to sharing a bottle of wine with friends over a meal. The apes definitely consume the equivalent of a standard drink or two’s worth of booze, but when they do so, they also have a full stomach and, perhaps, foster a closer relationship to their peers.
“You have a glass of wine with dinner; you talk to people. Maybe this is where it comes from evolutionarily,” Maro says.
