Boozy chimps fail urine test, confirm hotly debated theory

Recent findings published in the journal Biology Letters reveal that chimpanzee urine contains significant levels of alcohol byproducts. This discovery is attributed to their tendency to consume fermented fruits. This latest research supports a contentious theory concerning the evolutionary roots of human alcohol consumption. In 2014, biologist Robert Dudley from the University of California, Berkeley, introduced the 'drunken monkey hypothesis' in his book, arguing that the human attraction to alcohol can be traced back approximately 18 million years, coinciding with the emergence of great apes. According to Dudley, social bonding and food sharing evolved as ways for early humans to recognize fruit from afar. Initially, many scientists dismissed this theory, claiming that primates, including chimpanzees, do not typically eat fermented fruits or nectar. However, evidence supporting this behavior has accumulated over the past two decades. Earlier this year, researchers captured footage of wild chimpanzees sharing fermented African breadfruit, which contained measurable alcohol. Using a portable breathalyzer, they discovered that nearly all of the fallen fruit—about 90 percent—had some ethanol, with the ripest fruit containing the highest alcohol levels, equivalent to 0.61 percent ABV (alcohol by volume). Additionally, last September, Dudley and his colleagues published a paper that detailed their findings on ethanol concentrations in fruits favored by chimpanzees in the Ivory Coast and Uganda. They calculated that these chimpanzees consume around 14 grams of alcohol daily, roughly equivalent to one standard drink in the United States. When factoring in the chimps’ smaller body mass, their intake approximates nearly two drinks per day. To further investigate, researchers aimed to analyze the chimps’ urine for alcohol metabolites, similar to a study conducted on spider monkeys in 2022. This task was undertaken by Aleksey Maro, a UCB graduate student who spent last summer in Ngogo, collecting urine samples while living in trees to avoid the elements. With guidance from Sharifah Namaganda, a Ugandan graduate student at the University of Michigan, Maro devised a method to efficiently gather samples, including those from puddles on the forest floor.