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EXETER, United Kingdom — While humans have long enjoyed the pleasures and pains of drinking alcohol, an intriguing new study is challenging the long-held assumption that consuming ethanol (the intoxicating ingredient in booze) is uniquely human. Researchers reveal that our primate ancestors and many other animals may have been indulging in fermented fruits and saps full of ethanol for millions of years.
“We’re moving away from this anthropocentric view that ethanol is just something that humans use,” says senior author and behavioral ecologist Kimberley Hockings of the University of Exeter in a media release. “It’s much more abundant in the natural world than we previously thought, and most animals that eat sugary fruits are going to be exposed to some level of ethanol.”
The study takes a broad eco-evolutionary approach, finding that ethanol is actually quite common in the environment, with many wild fruits, saps, and nectars containing measurable levels of this substance. This includes everything from insects like vinegar flies to primates like chimpanzees and spider monkeys.
One key piece of evidence comes from genetic studies tracing the origins of alcohol-metabolizing enzymes back millions of years. For example, a mutation that dramatically increased ethanol processing efficiency arose around 10 million years ago in the common ancestor of humans, chimpanzees, and gorillas.
“The ADH change would have enabled our ancestors to consume fermented fruit and so exploit this niche with less risk of inebriation,” the authors explain in the journal Trends in Ecology & Evolution.
So, why would animals seek out this potentially toxic substance, or at the very least, intoxicate themselves? The research outlined possible benefits like providing calories, offering medicinal properties, and even altering cognition and behavior in ways that could be advantageous.
“On the cognitive side, ideas have been put forward that ethanol can trigger the endorphin and dopamine system, which leads to feelings of relaxation that could have benefits in terms of sociality,” says study first author Anna Bowland, another behavioral ecologist from the University of Exeter.
Of course, ethanol also carries risks, like impaired motor skills. However, the costs and benefits likely depend on an animal’s metabolic capabilities and ecological circumstances.
“Ethanol is ecologically relevant and… has shaped the evolution of many species and structured symbiotic relationships,” the researchers conclude.
Paper Summary
Methodology
To explore the prevalence and significance of ethanol in nature, the researchers conducted a comprehensive literature review. They scoured scientific papers and historical accounts for evidence of ethanol production in plants and its consumption by various animal species.
The team also examined genetic data to trace the evolutionary history of alcohol-metabolizing enzymes like ADH and ALDH. By reconstructing the molecular evolution of these enzymes, they were able to uncover adaptations that enabled more efficient ethanol processing in certain lineages, such as primates and fruit bats.
Additionally, the researchers looked at behavioral studies, both in the wild and in captivity, that documented animals’ responses to ethanol-containing foods and substances. This helped them understand the potential nutritional, medicinal, and cognitive benefits – as well as the costs – of ethanol ingestion for different species.
Key Results
Ethanol is commonly produced in nature through the fermentation of sugar-rich plant materials like fruits, saps, and nectars. Many animals, from insects to primates, have been observed consuming these ethanol-containing foods, either intentionally or accidentally.
Genetic evidence suggests that the ability to metabolize ethanol has been under strong evolutionary pressure in certain taxa, particularly those that are fruit- or nectar-feeding specialists. Potential benefits of ethanol consumption include nutritional, medicinal, and cognitive/behavioral advantages, though the specific costs and benefits likely vary by species.
Study Limitations
The researchers acknowledge that direct, scientific documentation of ethanol consumption in wild animals is still relatively limited. Much of the evidence is anecdotal or inferred from indirect sources like genetic data. More field studies and controlled experiments are needed to fully understand the prevalence and significance of ethanol use in nature.
Additionally, the researchers note that translating the impacts of ethanol on human health and behavior to other animals is challenging, as species can have very different metabolic capacities and physiological responses.
Discussion & Takeaways
This study fundamentally challenges the long-held assumption that ethanol use is uniquely human. By taking a broader, eco-evolutionary perspective, the researchers have shown that the ability to process and potentially benefit from ethanol has deep roots in the animal kingdom.
The findings suggest that ethanol may have played a more integral role in shaping the evolution of many species than previously recognized. From enabling access to calorie-rich resources to potentially influencing social and cognitive abilities, ethanol appears to be an important, if underappreciated, factor in the natural world.
Funding & Disclosures
This research was supported by grants from the Primate Society of Great Britain, the Wenner-Gren Foundation, the Canada Research Chairs program, and the Natural Sciences and Engineering Research Council of Canada. The authors declare no conflicts of interest.
