Humans' knack for consuming alcohol dates back around ten million years, long before Homo sapiens were a distinct species. A single gene mutation granted our evolutionary ancestors an enhanced ability to break down ethanol – drinking alcohol. Suddenly, some individuals could metabolize the alcohol from fermenting fruits on forest floors, converting it to energy and alleviating its toxic, incapacitating effects. Over time, these individuals survived and procreated more often, gradually granting almost all humans alcohol-imbibing abilities.
Fast forward to between 10,000 and 14,000 years ago, when, for the first time, humans transitioned from nomadic to agrarian lifestyles. Settling down and sowing crops had its perks – shelter, food, and social interactions were easier to come by – but it had its pitfalls as well. Perhaps the greatest was disease, particularly of the waterborne variety. Human clumping brought piles of human waste, which attracted unfriendly viruses and bacteria.
"As soon as there were mass human settlements, waterborne diseases like dysentery became a crucial population bottleneck," science writer Steve Johnson wrote in his book The Ghost Map.
But what are humans, who need water to live, supposed to do when the water sources around them are almost certainly polluted? For many, the solution was to drink alcohol. An effective antimicrobial, it also breaks down into water inside the human body. Cheers! Humanity had a safe(ish) way to hydrate.
"Whatever health risks were posed by beer (and later wine) in the early days of agrarian settlements were more than offset by alcohol's antibacterial properties," Johnson wrote. "Dying of cirrhosis of the liver in your forties was better than dying of dysentery in your twenties."
As drinking alcohol became the norm for thirsty humans around the globe, some scientists and historians theorize that people in societies where it was common evolved to produce more enzymes called alcohol dehydrogenases, thus making them better at metabolizing it.
"Many early agrarians lacked that trait, and thus were genetically incapable of 'holding their liquor,'" Johnson noted. "Consequentially, many of them died childless at an early age, either from alcohol abuse or from waterborne diseases. Over generations, the gene pool of the first farmers became increasingly dominated by individuals who could drink beer on a regular basis."
Most, but not all, humans are descended from these boozing farmers, and thus their bodies are built for imbibing alcohol relatively safely. Many indigenous peoples, descended from more nomadic humans, are notable exceptions. For example, alcohol abuse amongst Native Americans is far higher than the general population. According to Johnson, there's a simple explanation: "their ancestors didn't live in towns."
Alcohol is a waste product from yeast fermentation. That humans drank it to avoid waterborne disease is a fascinating instance of biological recycling. As Johnson wrote, "They drank the waste discharged by yeasts so that they could drink their own waste without dying in mass numbers."