Drunken Apes and the Rise of Civilization

New research reveals the primate origins of alcohol consumption—and how a single boozy mutation may have helped give rise to social complexity and large-scale civilizations.

Two monkeys play backgammon, David Teniers the Younger, 1635-1668.

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I: Wassailing

Eight months ago, on a chilly January night, I bundled up, traveled to a nearby village, and prepared to sing to apple trees.

One cannot rush straight into singing to an apple tree. For the incantations to work, a community must first process to the orchard, ideally in a long line, carrying blazing torches.

Once there, best practice dictates several rituals that must be performed: a collective howl (to scare away the evil spirits, obviously), followed by a ceremonial affixing of toasted bread to the branches, ensuring that the tree is well nourished. Suitably prepared, the tree may now be blessed with a song, beginning with the following lyrics:

Wassail, wassail, all over the town
Our toast it is white and our ale it is brown

This tradition is Anglo-Saxon, performed on or around Twelfth Night. The act of blessing and literally toasting the orchards—called wassailing—refers to the cries of ‘Waes Hael,’ which means good health. For more than a thousand years, it was a quintessential annual ritual in apple-rich parts of England. Without it, the harvest could fail, alcoholic cider would disappear, and a devastating catastrophe for lowly workers and high-born lords alike would inevitably unfold.

These elaborate rituals existed for a reason: alcohol has long been a central component of human social history. But just how central has only recently become clear, with help from better genomics and primate data.

Wassailing, that peculiar English penchant for blessing fruit trees to provide the community with bountiful alcohol, inadvertently offers a fascinating glimpse of a much larger story about what it means to be part of our species. Somewhat unexpectedly, that tradition may be linked—through the vast mists of ancestral time—to a single, consequential evolutionary tweak that uniquely affects our lineage of primates.

And in the last few weeks, scientists may have finally solved a longstanding biological puzzle—and helped to partly explain the well-lubricated origins of human social complexity and the rise of sprawling civilizations.

II: Buzzed creatures, great and small

To unravel this mystery, we must start with a more basic question: Do animals get drunk?

I don’t mean that in a “what would happen if we gave a badger a six-pack of Budweiser?” kind of way, but rather in a “do wild animals become intoxicated in the course of their normal lives?” way.¹ (The first kind of question has already been asked and answered in studies of dubious ethics, with some species eagerly consuming alcohol that was provided to them; elephants were known to happily consume as much as 35 cans of beer per day.)²

For some species, though, consuming alcohol happens naturally. When this occurs, it’s unclear whether this is merely an accidental byproduct of fermented fruits, or a cheeky enjoyment of the physiological and pharmacological effects of alcohol. Or both.

For example, a scholarly article from 1990 titled “Suspected ethanol toxicosis in two wild cedar waxwings,” describes how two of these medium-sized birds became intoxicated from consuming “overwintered hawthorn pommes,” which had begun to ferment. Alas, in their inebriated state, both birds fell to the ground and died.

Then, a little more than a decade ago, researchers began to pay more attention to the dietary behavior of non-human primates scrounging for food on the forest floor. The more they looked, the more they saw that some primate species would routinely eat fruit that had fallen from trees, partially rotted, and fermented.

In 2015, researchers also documented astonishingly sophisticated behavior of chimpanzees in West Africa, who were using leaves as tools to obtain and drink the fermented sap of the raffia palm. The study found that the sap varied in alcoholic intensity, but averaged 3.1% ABV—equivalent to weak beer. Some of the sap went as high as 6.9% ABV.

And then, there were the studies involving cocktail-loving vervet monkeys of St. Kitts. The species was brought to the island by slave traders 300 years ago. In recent decades, however, some of these mischievous rogues were known to eagerly snatch fruity cocktails from unsuspecting resort guests.

Researchers captured 1,000 of the vervet monkeys and studied their alcohol consumption. In a fascinating twist, it turned out that their imbibing preferences broadly lined up with human drinking patterns—including approximately similar proportions who were teetotal, moderate drinkers, or heavy drinkers. Five percent of the monkeys were binge drinkers.

III: Why don’t orangutans like booze?

By contrast, orangutans almost never consume fermented fruit or anything else even mildly alcoholic. This is not merely a difference of taste or dietary preference. Instead, it turns out that our human lineage of primates differs from those on the evolutionary path that gave rise to orangutans and gibbons. Our bodies differ in a crucial way: our lineage can metabolize ethanol—the kind of alcohol we drink—forty times better than orangutans.

In 2014, researchers got to the bottom of this genetic difference using clever phylogenetic techniques. In a nutshell, they were able to look at different gene sequences in living primates and, from that data, work backwards. By moving up the evolutionary tree of life from today’s genomic twigs to earlier branches millions of years earlier, they could recreate what the original genes would have been for our common ancestors.

One enzyme—called ADH4—drew their particular interest, since it is expressed in both our tongues and stomachs and has been shown to be essential for breaking down and digesting alcohol.

Once the researchers had determined what the “original” gene sequence had been for the ancestral form of ADH4, they tailored special bacteria to produce that precursor enzyme—and then tested how well it could metabolize alcohol. (This, on its own, is pretty cool; as Sedeer el-Showk wrote in Nature at the time: “they resurrected proteins that haven't been seen for millions of years… just to find out if they could break down alcohol.”)

With this study, the researchers were able to travel back 70 million years into our primate past and successfully identify the crucial mutation that, to this day, allows us to drink alcohol.

It happened—once—ten million years ago. It was just a single change in one amino acid, but it was a change that forever altered our relationship with alcohol. Here’s a visual representation of how effectively our lineage (which gave rise to chimpanzees, gorillas, and ourselves) metabolizes alcohol, compared to those earlier primates without that evolutionary tweak:

Why did that mutation happen? And why did it happen at that moment?

When a genetic change like this occurs, it’s tempting to reach for a neat-and-tidy post hoc explanation, something that skeptics in evolutionary biology dismissively label as “just so” stories. After all, nature is complex—and there are plenty of incredibly important evolutionary changes that occur purely due to chance, including those from genetic drift.

But the ADH4 enzyme mutation did coincide with important environmental changes that could help explain why it happened when it did.

Our distant primate ancestors evolved the ability to digest alcohol during the middle Miocene climatic transition, a period of cooling that produced rapid environmental shocks. The previously lush forests of East Africa gave way to “fragmented forests and grassland ecosystems.” Many species, including plenty of hominoid primates, went extinct because they were unable to cope with the new environment.

The fossils of those who did survive show evidence that some of those species began walking on their knuckles, evidence that suggests they became more ground-dwelling. Through some educated scientific guesswork, it’s plausible that the species that were able to best survive were those that clambered across the forest floor, scrounging on fallen fruits.

Any animal that could easily digest fermented fruits and the ethanol within would therefore have a survival advantage over everyone else, creating a sudden and intense selection pressure in favor of the ADH4 mutation. For those primates stuck with the old enzyme, they could only eat what was still ripe on the trees, creating a shorter time window for consuming an already dwindling supply of food.

But there were two problems with this hypothesis. First, nobody knew whether apes actually consumed much ethanol in their daily diets. Second, those who study the dietary habits of apes didn’t tend to differentiate between fruit on the tree and fruit on the ground, a crucial distinction needed to verify the hypothesis.

So, after more than a decade of speculation, a pioneering team of scientists decided to test the theory, measure the prevalence of fermented fruit in primate diets, and even coin a new term to describe that feeding strategy.

IV: Chimpanzees really like to scrump

As the scientists, led by Nathaniel J. Dominy of Dartmouth College, remind us: Leo Buss got it right when he wrote that “the history of ideas is paved by constraints of language.” If you want to study a concept, you must first name it, thereby placing it in an appropriate category.

Funes the Memorious and the Useful Lie of Categories

The scientists decided on the word “scrumping” to describe the foraging of fermented overripe fruits from the forest floor.³ The word comes from the Middle Low German word schrimpen, which means shriveled or shrunken—and is the etymological origin of an English word that refers to the gathering or stealing of apples that have fallen from the tree. (It’s the same etymological origin for scrumpy, an English west country alcoholic cider, and for scrumptious.)

What quickly became clear from their analysis is that scrumping happens quite a lot within our lineage of primates. And there’s probably good reason for it beyond caloric benefits. Through scrumping, chimpanzees and gorillas don’t have to climb trees in order to get food. That matters for two reasons:

1. It’s far more calorically draining to climb trees to forage;

2. It’s dangerous to climb trees, as primates can and do fall and injure themselves—even dying in the process.⁴

(As an important aside, it’s likely that humanity’s rotating shoulders and extending elbows initially evolved to more safely achieve “downclimbing,” in which our ancestral apes were able to lower themselves down from trees more delicately than monkeys. Moreover, I’ve written previously about how the evolution of our unique human shoulders, which are different from those of chimps, played a crucial role in reshaping human social hierarchies.)

But until the scientists gathered actual data, all the grand theories would remain informed supposition. So, the scientists examined thousands of hours of feeding behaviors among primates to see what proportion of consumed fruits were actually “scrumped.”

For orangutans, the figure was almost zero—0.8 percent of their overall total. On the other end of the spectrum, western gorillas got nearly two-thirds of their fruit from scrumping. For chimps, our closest non-human primate relatives, the figure was around a third.

Since chimps eat roughly 10 pounds of fruit per day, that means they’re routinely consuming a decent bit of alcohol.

This fresh evidence of widespread scrumping lends itself rather well to the wonderfully-named “Drunken Monkey Hypothesis.” That theory suggests that the evolutionary origins of consuming low-level ethanol through fermented fruit helped our ancestral primates survive, particularly because ethanol is a light molecule with a scent trail that can easily be carried by the wind.

Hungry primates could follow that scent to fermenting fruit and find life-sustaining calories even in difficult environments. However, this trait (which helped primates survive) later became maladaptive (or detrimental to survival) in humans when we learned how to distill liquor to higher concentrations through technological innovation. Once that happened, there was an evolutionary mismatch—between the original useful trait and the later expression of it in more recent centuries, culminating in the scourge of alcoholism.

But here’s where things get a little more interesting for our story. It’s plausible that this one little evolutionary mutation from ten million years ago—slightly altering a single amino acid—may also be part of the reason why civilization emerged during the Neolithic period, leading ultimately to the spread of larger, permanent settlements and the rise of complex civilizations.

V: Civilization, fermented

Seven years ago, researchers found evidence of the world’s oldest brewery—in Haifa, in modern day Israel. It was in operation 13,000 years ago. They found trace residue of alcohol made from barley and wheat, presumably used for ceremonial and ritual purposes. (Archaeologists think that this early alcohol probably had a porridge-like consistency.)

The global archaeological record of prehistoric alcohol consumption is abundant and geographically varied. There’s evidence of drinking alcoholic rice wine in 7000 BC, in the settlement of Jiahu, in modern-day China. Other findings put prehistoric booze in settlements in modern-day Iran, Mexico, Sudan, Georgia, you name it.

In other words, social complexity and alcohol consumption coincide throughout the historical and archaeological record. There is a remarkably strong correlation between people who turn to sedentary lifestyles in larger settlements and those who consume early versions of beer or wine or other similar fermented substances. This consistent correlation has spurred plenty of speculation, including articles such as “How Beer Gave Us Civilization,” that possibly overstate the case.

The Neolithic Revolution—a remarkably abrupt shift toward agriculture and permanent settlements—likely did not have a single cause. I’ve previously written about various explanations that draw on “Big Gods” who helped pave the way for more cooperation, or what I call the “war and peas” hypothesis (which centers the explanation on warfare and agricultural innovations).

But it is increasingly clear that alcohol played some role. Large tomes such as Alcohol and its Role in the Evolution of Human Society or scholarly articles such as “Pharmacological Influences on the Neolithic Transition” and “Alcohol and Social Complexity in Ancient Western Asia” weave compelling narratives on the crucial role of alcoholic drinks, boosted by archaeological and anthropological evidence.

For example, some early proto-states asserted themselves over the economy for the first time in regulating the production and distribution of beer, which didn’t just create early forms of bureaucratic regulation, but also shaped longer-term state development and centrally-managed inequality.

More speculative theories abound, in which alcohol helps account for our proliferation of cooperation, creativity, and culture. Jeffrey P. Kahn put it this way: evolution gave us survival instincts, which are all well and good, except they:

“…didn’t readily lend themselves to exploration, artistic expression, romance, inventiveness and experimentation — the other human drives that make for a vibrant civilization.

To free up those, we needed something that would suppress the rigid social codes that kept our clans safe and alive. We needed something that, on occasion, would let us break free from our biological herd imperative — or at least let us suppress our angst when we did.

We needed beer.”

Kahn argues that social cooperation was lubricated by alcohol, which may be an amusing way of evaluating the history of our species, but nonetheless has a grain—pun intended—of truth to it. Perhaps just a touch flippantly, Charlie Bamforth of UC-Davis put it this way:

Beer is the basis of modern civilization. Because before beer was discovered, people used to wander around and follow goats from place to place. And then they realized that this grain [barley] could be grown and sprouted and made into a bread and crumbled and converted into a liquid which gave a nice, warm, cozy feeling. So gone were the days that they followed goats around. They stayed put while the grain grew and while the beer was brewed. And they made villages out of their tents. And those villages became towns, and those towns became cities.

I’m skeptical that alcohol was the key ingredient in the Neolithic Revolution. But I also think it’s undeniable that the rise and evolution of human social complexity would have been considerably different without alcohol. Later, wine played a role in Roman imperialism. The hops trade is part of the origin story of Western capitalism. Rum played a huge role in the slave trade.

We are all descendants of those dark and stormy histories, individual outgrowths of a contingent past that was made possible—at least in part—by a single amino acid tweak in our primate ancestors that likely happened just once, ten million years ago. And all those hungry apes wanted was to survive for yet another day, helped along by a little bit of slightly fermented fruit.

So, next time you sit down with a glass of wine, or beer, or something more potent, consider a fitting toast to that evolutionary mutation lurking within all of our bodies. Waes Hael!

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1. A drunken badger did allegedly disrupt traffic in Germany but this is not a widely observed behavior. (If you want to go down an eccentric astronomy rabbit hole, look up the story of Tycho Brahe’s drunken pet moose.) Aside from alcohol in the animal kingdom, some lemurs in Madagascar have been known to lick millipedes, using the secretions to repel insects (with a simultaneous narcotic effect that puts the lemurs into a blissfully intoxicated state):

2. Previous studies which showed elephants getting buzzed on the fruit of marula trees were probably bogus (the amount they’d have to consume is implausible).

3. This is not the same as the less PG form of scrumping that lurks in Urban Dictionary.

4. Anything that tends to kill individuals (particularly before they’re able to reproduce) certainly matters for evolution.