Humans appear to be the only species that seek out a state of inebriation for fun- a couple of pints here and there pretty much sums up a lot of people’s summer plans. But anecdotal evidence suggests that other animals wouldn’t say no to a tipple or two, just not in quite the same fashion as us.
Dietary ethanol is where it all starts. And from there, it can be a slippery slope with some animals that may actively seek out alcohol. Human eyes were first opened to ethanol way before we started to intentionally produce it for consumption, dating back to frugivorous (fruit-eating) ancestors 10 million years ago and their exposure to alcohol naturally occurring in ripening fruits. In the same way, animals encounter ethanol, with natural fermentation processes producing ethanol concentrations up to 8.1% in fruits. That’s pretty much the same as a K Cider.
Primates are very sensitive to alcohol odours and can use olfactory cues from alcohols when foraging. Data even shows that some primates prefer consumption of solutions containing ethanol when they are available, with some of these behaviours explained by genetics.
In humans, chimpanzees, bonobos, and gorillas, a mutation known as ADH7, in the alcohol dehydrogenase class IV gene, improves efficiency of alcohol metabolism. So you can thank your genes for all that heavy-weight behaviour. This mutation evolved to coincide with increased terrestrial habits which may have led to increased exposure to fermenting fruit on the forest floor.
A study conducted in 2020, by Janiak et al. at the University of Calgary in Canada, investigated 85 different species of mammals and how well they can handle their alcohol. The study revealed that natural selection accounts for part of alcohol tolerance in an organism, with ADH7 selection intensified in animals with diets high in fruit or nectar, and selection relaxed in those without. This shows the detrimental effect that over-consumption of alcohol can have on an organism, revealing that through evolution several organisms, including humans, have evolved to enhance alcohol metabolism to reduce negative impacts.
Mammals whose diets mostly lack fruit or nectar, including cows, elephants, and horses, have lost functional alcohol dehydrogenase enzymes so metabolise alcohol poorly. In fact, African elephants are famous for their alcoholic tendencies, with widespread lore telling tales of these elephants consuming fallen and fermented marula fruit causing intoxication. Whether these stories are true remains a question that researchers hope to elucidate in the future, as some studies suggest that elephants simply couldn’t consume enough of the fruit to proceed to a state of drunkenness.
It appears that other animals are also exposed to dietary alcohol and some seem quite partial to it. Fermented palm sap is sought out by chimpanzees who routinely fashion leaf sponges in order to access the alcohol, and signs of inebriation have been seen in Swedish elk following consumption of rotten apples in the autumn. Birds aren’t exempt from a little drunkenness either, consuming overwintered berries that ferment in spring with excessive consumption proving fatal. In Egyptian fruit bats, consumption of more than 1% alcoholic substances disrupts flight and echolocation abilities.
So, if you’re worried about coming out of lockdown a lightweight, just remember that genetics is on your side- and at least you don’t have the pressure of flight and echolocation like bats do. Maybe take it easy at first though.
Image: Heidi Januszewski.