Imagine spending your entire summer collecting chimpanzee urine while suspended in trees with an umbrella as protection. Welcome to the life of Aleksey Maro, a UC Berkeley graduate student who decided this was exactly how he wanted to contribute to science. His sacrifice, it turns out, has helped crack one of the more bizarre debates in evolutionary biology: whether our love of alcohol traces back millions of years to our primate ancestors.
The answer, based on his findings, is a pretty definitive yes.
The Drunken Monkey Theory Gets Real
Back in 2014, Robert Dudley published “The Drunken Monkey,” a book that proposed humans have been drawn to alcohol for roughly 18 million years, not because we’re inherently reckless, but because our ancestors evolved to seek out fermented fruit. The academic community largely rolled their eyes. Sure, it made for a catchy book title, but come on. Primates don’t actually hunt down boozy snacks, do they?
They absolutely do.
The evidence has been piling up over the last decade. Researchers caught chimps on film sharing fermented African breadfruit with measurable alcohol content. They measured the fruit with portable breathalyzers and found that 90 percent of fallen fruit contained ethanol, with the ripest specimens hitting around 0.61 percent ABV. That’s not nothing. The math got wilder when scientists calculated that these chimps were consuming roughly the equivalent of one standard drink per day, or closer to two when adjusted for their body weight.
But metabolites in urine? That’s the smoking gun nobody expected.
When Urine Tells the Story
Maro and his team tested 20 urine samples collected from wild chimps in Uganda using the same immunoassay strips that measure alcohol in human subjects. Sixteen of those samples contained significant levels of ethyl glucuronide, the byproduct your body produces when it metabolizes alcohol. We’re talking levels that would indicate one to two drinks in a human.
The implications are kind of wild. These aren’t accidentally tipsy chimps stumbling through the forest. They’re consistently consuming enough fermented fruit that their bodies show measurable signs of ethanol processing. Their physiology is literally adapted to handle this stuff.
What’s particularly interesting is who wasn’t drinking. Female chimps in estrus and juveniles showed no evidence of alcohol metabolites. That detail alone opens up new questions about how fermented fruit affects fertility cycles and whether there’s some biological wisdom at play here that we don’t yet understand.
What This Means for Human Evolution
The connection between science and our everyday habits is rarely this direct. We’ve all wondered why humans uniquely obsess over alcohol across virtually every culture. It seems bizarre from an evolutionary standpoint. Why would we develop such a powerful attraction to something that impairs our judgment and slows our reflexes?
The answer might be simpler than we thought: because our ancestors were doing it too.
If chimps are regularly consuming fermented fruit, and our lineage split from theirs millions of years ago, there’s a decent chance our primate ancestors were stumbling through African forests in similar states. Natural selection didn’t punish this behavior because the fermented fruit also provided calories, and the ability to smell and identify overripe (and thus more nutritious) fruit became advantageous. Our brains rewired themselves to find alcohol rewarding because it was a reliable marker of food energy.
That doesn’t excuse modern excess, obviously. But it does suggest that our relationship with alcohol is baked into our biology in ways we’re only now beginning to understand.
The Work Isn’t Done Yet
Dudley himself acknowledges the remaining gap: nobody has definitively proven that chimps actively prefer higher-alcohol fruit over lower-alcohol alternatives. They might just be eating whatever fermented fruit is available without being selective about ethanol content. That’s the next frontier for researchers brave enough to spend another summer in African forests with a collection apparatus and questionable accommodations.
Other scientists are already moving forward. Camera traps caught various animals consuming large quantities of the same fermented fruit, suggesting this pattern might extend across multiple species. A colleague is currently sampling fruit bat urine in Madagascar to see if the phenomenon shows up there too.
The drunken monkey hypothesis went from fringe theory to something that demands serious consideration the moment those urine samples came back positive. And honestly, that’s how good science works. You get skeptics, you gather evidence, and eventually the evidence wins. Sometimes that evidence comes from the least glamorous source imaginable, collected by someone sleeping in a tree with an umbrella.
The real question now isn’t whether our ancestors drank. It’s how deeply fermented fruit shaped our entire species’ trajectory.
