Ancient Ape Foraging for Fallen Fruit May Have Shaped Human Alcohol Tolerance

Over 10 million years ago, ancient African apes gained extra nutrition by eating fallen, fermented fruit—a behavior that may have laid the evolutionary foundation for humans' alcohol tolerance. A recent BioScience study provides new evidence for the "drunken monkey hypothesis" and refers to this fruit-foraging behavior as "scrumping".

Ethanol, the alcohol naturally present in fermenting fruit, can cause mild intoxication in many animals. Humans have been brewing alcoholic beverages for at least 8,000 years, with some evidence suggesting that early grain domestication may have been driven more by brewing than bread-making. Evolutionary biologists propose that decaying, fermented fruit—easily located by smell—offered a unique nutritional resource to early apes that other animals largely avoided.

A key clue to when human ancestors acquired this tolerance came from a 2015 analysis of alcohol-metabolizing genes across 18 primate species. It found that humans, chimpanzees, and gorillas share a mutation that makes a key enzyme 40 times more efficient. If this mutation arose in their common ancestor, it dates back at least 10 million years. However, data had been lacking on whether ape diets actually included enough fermented fruit to support the hypothesis.

To address this gap, researchers at Dartmouth College analyzed field records of ape feeding habits. They found that foraging for fallen fruit accounts for 25–62% of fruit consumption in African apes (chimpanzees and gorillas), whereas orangutans—more distantly related to humans—rarely eat fruit from the ground. This difference may correlate with the presence or absence of the mutation.

The researchers conclude that primates’ relationship with fermented food has deep evolutionary implications. By the time humans began brewing around 10,000 years ago, our bodies were already well adapted to metabolize alcohol—an adaptation that may trace back to ancient apes' foraging for fallen fruit.