Animals Like to Get Drunk, Too
From fruit flies to elephants, lots of creatures great and small enjoy a drink-or even a bender
By Ian Tattersall and Rob DeSalle
Dec. 17, 2015
Should holiday festivities leave you with a pounding hangover, here’s a consoling thought: Humans aren’t the only animals that get blotto.
Elephants in southern Africa often binge on the naturally fermenting fruit of the marula tree and lumber unsteadily away afterward. Howler monkeys in Central American forests can become exuberantly tipsy after feeding on the lightly alcoholic ripe fruit of the Astrocaryum palm, sometimes downing the equivalent of 10 bar drinks in a session. Scientists in western Africa have recently discovered that our close relatives, the chimpanzees, go to the trouble of making sponges out of crumpled leaves to soak up the lightly fermenting juices that exude from raffia palms. Even the humble fruit fly has been known to sidle up to the bar: Flies exposed to moderate levels of alcohol fumes live longer than their teetotaling counterparts, and unfortunate male flies that have been deprived of sex may well turn to alcohol for solace.
So why are creatures across the animal kingdom attracted to alcohol? After all, ethanol-the kind of alcohol molecule that most of us drink-is highly toxic to most organisms: One unfortunate hedgehog reportedly expired from drinking egg liqueur before its blood-alcohol level had reached half the legal limit for driving in New York state. Even the very organisms-yeasts and tiny unicellular fungi-that produce the alcohol in wine are vulnerable to its effects: Once ethanol levels rise above about 15% in the fermenting grape juice, they die.
So why do these tiny organisms produce the stuff in the first place? They have pretty good reasons. The amount of alcohol they normally generate is pretty low-but still enough to be toxic to most potential microbial competitors. The competition for resources is intense even for microbes, and evolutionary biologists think that ancient yeasts first produced alcohol as a weapon for clearing ecological space around them.
Evolutionary advantages to alcohol tolerance can also be found for much bigger organisms. Those fruit flies, for example, live off sugars and other products of plants and fungi, so ethanol naturally occurs in their diet. Accordingly, they have acquired an enzyme (known as alcohol dehydrogenase) to let their bodies break down those toxic ethanol molecules. And a jilted fruit fly may actively seek out ethanol because it promotes the production in their brains (yes, fruit flies have brains) of a molecule that will make it feel better.
The evolutionary calculation for acquiring alcohol tolerance in Homo sapiens might have been similar. Inspired by those tipsy howlers, the Berkeley physiologist Robert Dudley has proposed the “drunken-monkey hypothesis” of human inebriation. He argues that we are descended from largely fruit-eating primate ancestors who were drawn to the ripest, most nutritious fruit by the scent of naturally fermented ethanol. Being able to tolerate ethanol would have given those ancestors a huge dietary advantage.
The improbable world champion of handling naturally occurring booze is the tiny pen-tailed treeshrew of Malaysia. Weighing only a few ounces, these diminutive creatures (generally thought to resemble our own ancestors from the beginning of the Age of Mammals) regularly binge on vast quantities of fermented palm sap. But they seem to have evolved specialized mechanisms for detoxifying all that ethanol: Even after a bender, they show no signs of inebriation, which could have tempted hungry predators.
Sugars are everywhere in nature, so it is hardly surprising that many primates can handle small quantities of the ethanol that can result. But we humans have far surpassed those howler monkeys (even if we’re no match for treeshrews). Researchers have recently learned that a mutation some 10 million years ago in the alcohol dehydrogenase gene greatly increased alcohol tolerance in the ancestor shared by humans and African apes.
That enhanced ability to deal with ethanol emerged at a crucial time in human evolution, just as our first apelike, bipedal ancestors were taking their initial upright steps on the ground. The context is particularly suggestive: Ripe fruit drops to the ground and becomes a powerful source of alcohol as it rots-and our ancestors are finally down there to find it. We won’t argue that alcoholic fruit was the thing first tempting them to terra firma, but once both the fruit and the ancestral hominids were on the ground, the bar was open.
From that moment on, humans have been enthralled by alcohol. In the 8,000 years since wine was invented somewhere in the Caucasus, we have used it for all sorts of stabilizing social purposes-think of sacramental wine or the boozy ancient Greek symposium, the fount of Western civilization.
Few pleasures in life are more satisfying than sharing a splendid bottle of wine around a dinner table filled with friends. But alcoholic excess has also meant appalling human wretchedness. Alcohol has long shown us to be all too human, simultaneously creative and destructive; but it reminds us that we’re animals too.