Chimpanzees and Fermented Fruit
Recent research published in Biology Letters reveals that chimpanzees in the wild consume significant amounts of fermented fruit, resulting in detectable levels of alcohol byproducts in their urine. This finding adds weight to a long-debated theory about the evolutionary origins of humans’ fondness for alcohol. The idea, proposed by biologist Robert Dudley in his book ‘The Drunken Monkey: Why We Drink and Abuse Alcohol,’ suggests that the attraction to alcohol dates back millions of years to the great apes. Dudley’s hypothesis faced skepticism due to the belief that primates do not typically consume fermented fruit or nectar.
However, evidence of primates consuming fermented substances has increased over the years. Earlier this year, researchers captured footage of wild chimpanzees sharing fermented African breadfruit, which contained measurable alcohol content. This was the first documented instance of nonhuman great apes sharing alcoholic foods in the wild. The fruit’s alcohol content was measured using a portable breathalyzer, with results showing that 90 percent of the fallen fruit contained ethanol, and the ripest fruit had alcohol levels equivalent to 0.61 percent ABV.
Quantifying Alcohol Consumption in Chimps
In a separate study, Dudley and his colleagues measured the ethanol content of fruits favored by chimpanzees in the Ivory Coast and Uganda. They found that these chimps consume around 14 grams of alcohol per day, roughly equivalent to a standard alcoholic drink in the United States. When adjusted for the chimps’ lower body mass, this translates to nearly two drinks per day for a human. These findings further support the idea that chimps have a natural inclination towards consuming alcohol-laden fruits.
The next logical step was to analyze the chimpanzees’ urine for alcohol metabolites, a method previously used in a 2022 study on spider monkeys. This would provide a clearer picture of the amount of ethanol-rich fruit consumed by chimps daily. Collecting urine samples from wild chimpanzees is no easy task, but it was undertaken by Aleksey Maro, a graduate student from the University of California, Berkeley. Maro spent the summer in Ngogo, Uganda, employing innovative methods to gather samples, such as using plastic bags fashioned into shallow bowls to catch urine.
Implications for Human Evolution
The findings from these studies have significant implications for understanding the evolutionary roots of human alcohol consumption. The ‘drunken monkey hypothesis’ posits that early humans and their primate ancestors developed a taste for alcohol due to the nutritional benefits of consuming fermented fruits. This behavior may have contributed to the social and communicative evolution of these species, enabling them to identify and share valuable food sources from a distance.
While the hypothesis remains controversial, the growing body of evidence suggests that the consumption of alcohol-laden fruits is a natural behavior among primates. This challenges the notion that alcohol consumption is solely a human cultural phenomenon. As research continues, it may provide further insights into the complex relationship between primates and alcohol, shedding light on the evolutionary pathways that have shaped human behavior.
Facts Worth Knowing
- •💡 Chimpanzees consume around 14 grams of alcohol per day, equivalent to a standard drink in the US.
- •💡 90% of fallen African breadfruit consumed by chimps contains ethanol, with the ripest fruit at 0.61% ABV.
- •💡 The ‘drunken monkey hypothesis’ suggests human attraction to alcohol dates back 18 million years.
