More than 10 million years ago, ancient apes in Africa obtained additional nutrients by eating fallen and fermented fruit, a behavior that may have laid the foundation for the evolution of alcohol tolerance in humans. Research recently published in BioScience provides new evidence for the "drunken monkey hypothesis" and names the behavior of apes eating fruits dropped from the ground "scrumping."
Ethanol is a form of alcohol found naturally in fermented fruits, and many animals become "tippy" from eating this type of food. Humans began brewing alcoholic beverages as early as 8,000 years ago, and the domestication of grains may have been originally for brewing wine rather than making bread. Evolutionary biologists propose that because rotten, fermented fruit is easily located by scent, ancient apes that were able to eat it gained additional resources that other animals shunned.
A key clue as to when our ancestors acquired this ability came from a 2015 analysis of alcohol-metabolizing genes in 18 primate species. The study found that humans, chimpanzees and gorillas share a genetic mutation that increases the efficiency of coding enzymes by 40 times. Assuming this mutation was present in their common ancestor, it could be traced back to at least 10 million years ago. However, scientists lack data to prove whether the amount of fermented food consumed by apes is sufficient to support the "drunken monkey hypothesis".
To fill this gap, researchers at Dartmouth College in the United States analyzed ape eating data in field records and found that the "fruit picking" behavior of African apes (chimpanzees and gorillas) accounts for 25% to 62% of their fruit intake, while orangutans who are distantly related to humans almost do not eat ground fruits. This difference may be related to the presence or absence of genetic mutations.
Researchers believe primates' relationship with fermented foods has profound evolutionary significance. When humans started making wine about 10,000 years ago, their bodies already had the ability to metabolize alcohol. This adaptation may have originated from the "fruit picking" behavior of ancient apes.