Drunken Monkeys!

Good morning, sunshine. Or is it afternoon already? Did you have fun last night? How’s your head? Yep, you know you’re not supposed to mix tequila with Kahlua. I’m going to take advantage of this excruciatingly bright day in New Mexico to discuss a subject close to my heart, my aching brain, and my liver: Alcohol tolerance and abuse in the animal kingdom.

One of the many great things about booze is that it occurs naturally in the wild. Fermentation, the process by which a yeast transforms sugar into alcohol (and its by-product, carbon dioxide), needs no brewmaster or whiskey still. Yeast is blowing freely in the wind, and wild grapes were turning to wine long before we were cultivating chardonnay. Nutritionally speaking, alcohol is a double-edged sword: it’s extremely energy-rich, but it’s also toxic and makes you fall down. So it makes sense that animals which eat fruit would develop a tolerance to alcohol, gaining its energy while avoiding getting so drunk that they start hitting on their predators at the bar. (Or, if you’re a fruit bat, flying into a tree.) And the tolerance these animals have for liquor would put the most gin-blossomed tippler to shame.

Meet the greatest drinker in the world: the pen-tailed tree shrew. This tiny, unassuming nocturne from the rainforests of Southeast Asia may not look like a heavyweight, but pound-for-pound, it could drink you under the table. After all, it subsists entirely on a diet of palm nectar which is fermented by wild yeast to a fine 3.8 alcohol content. To mimic the tree shrew, you’d have to survive on only beer for your entire life. (Which is technically possible, I’ve heard from a bartender friend, but not recommended.) Despite consuming what would be, for us, the equivalent of nine glasses of wine a day, and having a blood alcohol level that is constantly above any country’s legal limit, the tree shrew remains sober. How it metabolizes its alcohol so efficiently is still a mystery, but scientists believe that the answer, when found, could present us with a cure for alcohol poisoning, and perhaps a weapon against alcoholism. Right now, most alcohol research is done on lab rats, and rodents tend to avoid alcohol by preference. But the tree shrew actually resembles the earliest primates on a taxonomic level, and could give us insight into our own alcohol tolerance and predilections. What’s more, we’re not the only primates out there that like to hit the sauce.

This is you vs. a pen-tailed tree shrew.

First, let’s consider the mutualism of the palm and the shrew. It’s obvious why the shrew would develop the tolerance for alcohol, given that evolution would select against tree-dwelling animals that get staggeringly blotto. But why does the bertam palm, a spiky and uninviting plant that, according to one researcher, “smells like a brewery,” allow its nectar to ferment in the first place? The tree shrew is a pollinator of the palm, so the benefit of having energy-rich nectar is clear. But is the palm fermenting by accident, or did it, in a way, “choose” to make its nectar open to wild-blown yeast? If by accident, then the tree shrew simply evolved to tolerate its high alcohol content to take advantage of a nutritious food source. But it is possible that the shrew doesn’t just have a tolerance — it has a dependence. Like an unscrupulous bartender, the palm may have tricked the shrew into being a constant, reliable pollinator by getting it hooked on the hard stuff. If that’s the case, the shrew handles its habit well. With other alcoholic animals, that’s not always the case.

As you’ll hear in the voiceover, these vervet monkeys were brought by pirates from Africa to the Caribbean island of St. Kitts, where their taste for rum and grog has been passed down over the generations. Like many humans, the vervets have formed a permanent tropical alcoholic culture: a monkey Margaritaville. But monkeys don’t handle their hooch as well as fruit bats and tree shrews, as you’ll see by their drunken stumbling. Then again, with no natural predators on the island, they don’t have to. They can get sloshed without consequence. So it’s not the energy they seek in the alcohol, but the intoxication.

The evolutionary downside to drunkenness is clear, but could there be an evolutionary upside? Yes. First, there’s the obvious advantage of alcohol often leading to an increase in offspring. Anything that facilitates an increase in mating tends to be selected for, and alcohol is certainly that. But it may be its role as a social lubricant that keeps a taste for alcohol in our genes. Getting drunk with friends, sharing the experience of intoxication, can serve to strengthen social bonds while simultaneously loosening the straps of social hierarchy. As any grooming ape can tell you, culture is incredibly important to survival. The first ancestor of Australopithecus that plucked fermented berries from the vine and shared them with his troupe could have rejected them. But he didn’t. He also could have gotten eaten by a lion, the prehistoric equivalent of drunk driving. Probably more than a few impaired ape-men were run down by predators, or got stabbed in bar fights around the cave fire. But something in those berries conferred enough advantage to outweigh alcohol’s deleterious effects, so a tolerance developed, along with a gene for alcohol abuse, along with a culture. If what survives in our genes and culture is what is useful, or is linked to something useful, then intoxication and mankind’s search for it has somehow aided our eventual, if temporary, domination of the planet. We may truly and literally be party animals.