Published by SFGATE, photo courtesy of Giovanni Mereghetti/UCG/Universal Images Group via Getty

Chimpanzees — one of our closest living relatives — could throw back roughly the equivalent of two alcoholic drinks every day by guzzling ripe fruit, UC Berkeley scientists report.

The new findings published Wednesday in Science Advances support the “drunken monkey” hypothesis, the idea that humans got our taste for alcohol from our primate ancestors. Now, the same UC Berkeley biologist who developed that theory has revealed in this new study just how much ethanol — the intoxicating ingredient in our cocktails — chimps might consume.

“I was surprised by the numbers we found,” Robert Dudley, a UC Berkeley professor of integrative biology and the study’s senior author, told SFGATE. “I had thought for a long time that these fruit eaters would be getting high daily dosages of ethanol, given they’re consuming larger volumes of fruit — and it’s quite clear that it’s actually a lot.”

To settle on the estimate of two drinks per day, the UC Berkeley researchers and their colleagues conducted extensive field research in chimpanzee hotspots in Uganda’s Kibale National Park and Ivory Coast’s Taï National Park. The team picked up figs and other fruits from underneath the trees where chimps feasted and tested their ethanol content through three different methods, including with a breathalyzer-like device. Generally, ripe fruit has higher ethanol levels, as more of the natural sugars ferment.

The fruit had an average alcohol content of 0.3% by weight — far less than even the weakest, most watery beer. But the chimpanzees ate on average around 10 pounds of this fruit per day, according to prior research. The scientists were able to calculate that both male and female chimps consumed about 14 grams of pure ethanol per day. Although that’s about one standard drink per day for a person, adjusting for chimps’ lower body mass means they’re consuming the alcohol content of about two drinks daily.

But chimps aren’t acting like they’re getting a buzz from their alcohol.

“They’re consuming throughout the course of the day, so it’s very different from what humans are doing,” Dudley said. “And although these are non-trivial dosages, we don’t know what the behavioral or physiological effects would be on the chimps.”

One of the main lingering questions is whether the chimps are actually picking and choosing fruit with high ethanol levels on purpose.

Dudley said there are many theories as to why the chimps would seek out fruits with more ethanol. Choosing the fruit with the highest sugar content would give them more energy. Or maybe those high-ethanol fruits are more pleasurable to eat — think wine with dinner — or they might even play a role in social bonding, like when they share their tasty finds.

Nate Dominy, a Dartmouth College biological anthropologist, commended the scope of the study and the methods of measuring ethanol. He didn’t participate in this research but thinks it’s a step toward more understanding about our primate counterparts and their habits.

“Many people have been resistant to the idea that ethanol is omnipresent in fruits because they simply don’t see animals behaving in a way that suggests that,” said Dominy, who contributed to a different study that created the term “scrumping” for gathering or stealing fallen fruit. “But I think what they found is really compelling and is going to help shut the door on that debate.”