Chimpanzee pee reveals how our primate cousins ​​get drunk on fermented fruit

Chimpanzee pee reveals how our primate cousins ​​get drunk on fermented fruit

By KR Callaway edited by Claire Cameron

A chimpanzee might not walk into a bar, but these monkeys have a taste for alcohol.

In particular, they use alcohol in fermented fruits, from figs to star apples to local stone fruits. As these fruits ripen, they produce sugar, which combines with yeast to produce ethanol. While the amount of ethanol in a single piece of fruit is very small, chimpanzees are voracious, and some eat about 4.5 kilograms of fruit a day. Old research suggested that, adjusted for body weight, a chimpanzee could consume the equivalent of more than two standard alcoholic drinks a day. But evidence of this consumption had been elusive – until now.

A new analysis of chimpanzee pee confirms that the monkeys ingest enough alcohol to show up on field tests of their urine. The finding may shed light on how the psychoactive substance affects the animals’ behaviour.

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“We can’t jump to conclusions, but there are many ways in which the psychoactive influence of alcohol would be useful for chimpanzee behavior and ecology,” says Aleksey Maro, PhD researcher at the University of California, Berkeley, and lead author of the study.

Maro and his team followed a group of chimpanzees at Ngogo, a research site in Uganda’s Kibale National Park. They collected the monkeys’ urine and identified the presence of alcohol in the samples on the spot with dipstick assays commonly used to test humans for alcohol consumption.

We know that alcohol can significantly affect human behavior, either by impairing our cognition or affecting our motor function – not to mention by causing hangovers. But it is possible that consuming alcohol may provide some benefits to chimpanzees, such as by reducing anxiety while guarding their territory or by increasing socialization within their group.

Some researchers doubt that chimps seek out these effects in the same way that humans might pursue some light relief at a bar—and it’s unclear whether chimps feel alcohol’s effects in the same way we do.

“In a way, alcohol makes people more like chimps,” says Kevin Langergraber, a chimpanzee ecologist at Arizona State University, who was not involved in the study. “I have been to Ngogo many times when the chimpanzees eat these super crops Chrysophyllum fruit and never noticed the chimpanzees behaving strangely.”

Maro says a better way to think about the chimps’ alcohol intake is to compare it to sharing a bottle of wine with friends over a meal. The monkeys definitely consume the equivalent of a standard drink or two of booze, but when they do, they also have a full stomach and perhaps create a closer relationship with their peers.

“You have a glass of wine with dinner, you talk to people. Maybe this is where it comes from evolutionary,” says Maro.

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