Primate Happy Hour

Humans might not be the only ones with a taste for alcohol: Wild chimpanzees seem to be getting a daily buzz without ever touching a bottle.  

A new study analyzed the ethanol content of fruit eaten by chimpanzees in their native African habitat and found that the primates could be consuming the equivalent of more than two standard alcoholic drinks a day.  

It is unclear whether they actively seek out fruit with high ethanol levels, namely, riper fruit with more sugars to ferment. However, ethanol is available via the different fruits they usually consume, meaning that alcohol is a regular part of their diet and likely was a part of the diets of human ancestors. 

“Across all sites, male and female chimpanzees are consuming about 14 grams (0,49 ounces) of pure ethanol per day in their diet, which is the equivalent to one standard American drink,” study author Aleksey Maro said in a statement. “When you adjust for body mass, because chimps weigh about 40 kilos (88 pounds) versus a typical human at 70 kilos (154 pounds), it goes up to nearly two drinks.” 

The team sampled 21 species of fruit at two chimp study sites, Ngogo in Uganda and Taï in the Ivory Coast. According to primatologists, chimps at these sites consume on average about 10 pounds of fruit per day, making up about three-quarters of their diet. 

The team collected fallen fruit, stored it in air-tight containers, and then froze it to prevent further ripening. They collected samples on three different occasions and used different methods to test alcohol percentages – a portable gas chromatograph, a chemical test, and a semiconductor-based device similar to a breathalyzer, Cosmo Magazine explained. 

All the methods reported similar percentages, and the study results found that the fruit had an average alcohol content of 0.32 percent by weight at Ngogo and 0.31 percent at Taï. 

The most frequently consumed fruits at each site – which were the fig Ficus musuco, at Ngogo, and the plum-like fruit of the evergreen Parinari excelsa at Taï – had the highest alcohol content. 

“If the chimps are randomly sampling ripe fruit, then that’s going to be their average consumption rate, independent of any preference for ethanol,” said study author Robert Dudley. “But if they are preferring riper and/or more sugar-rich fruits, then this is a conservative lower limit for the likely rate of ethanol ingestion.” 

Researchers observed that fruit consumption occurs throughout the day and that the chimps did not show overt signs of intoxication.  

Chronic low-level exposure indicates that the common ancestors of humans and chimps were also exposed to daily alcohol intake from fermenting fruit, a nutrient that is now missing from the diets of captive chimps and many humans. 

“Chimpanzees consume a similar amount of alcohol to what we might (have) if we ate fermented food daily,” Maro said. “Human attraction to alcohol probably arose from this dietary heritage of our common ancestor with chimpanzees.” 

Dudley – who, 20 years ago, first hypothesized that humans inherited their alcoholic taste buds from primate ancestors – published a study on birds this year where the feathers of 10 out of 17 species they analyzed showed they likely had substantial amounts of ethanol in their diet.   

“The consumption of ethanol is not limited to primates,” says Dudley. “It’s more characteristic of all fruit-eating animals and, in some cases, nectar-feeding animals.” 

Dudley believes animals may gravitate toward ethanol-rich food due to its distinct smell, as it helps them find food with higher sugar content, which provides them with more energy. Moreover, it is possible that sharing alcoholic fruit has a social function among primates, just as it does for humans.