Why You’re Such a Lightweight: A Selection from Joseph Henrich’s The Secret of Our Success (2017)

“In mammals, the alcohol from rotting fruit and other sources is broken down by enzymes produced by alcohol dehydrogenase (ADH) genes and eventually processed into energy and metabolites in the liver. However, if the rate of inflow of alcohol (ethanol) into the liver is too high, then it ‘overflows,’ going into the heart and then spreading throughout the body. Intoxication ensues. Most primates aren’t particularly good at processing alcohol. However, about 10 million years ago, when our common ancestor with gorillas came down from the trees to spend more time on the ground, rotting fruit probably became a more important food source, so our ape lineage evolved a higher tolerance for consuming alcohol. This ancient adaptation appears to have set the stage for much more recent culture-gene coevolution, as humans have experienced a great deal of evolutionary action on various alcohol-processing genes since the origins of agriculture.

Let’s consider just one of those genetic changes. Between 7000 to 10,000 years ago, the DNA on one of these ADH genes (ADH1B) on chromosome 4 flipped a bit, causing it to code for the amino acid histidine instead of arginine. The evidence seems to suggest that this new version of the ADH1B gene metabolizes alcohol much more efficiently in the liver. Perhaps, more important, the rapid breakdown of alcohol produces high levels of acetaldehyde, which causes dizziness, increased heart rate, nausea, weakness, overheating, and a flushing of the skin. The unpleasantness of this flushing reaction reduces people’s susceptibility to alcoholism and parallels the effects created by drugs used to treat alcoholism. Estimates vary, but possessing the booze-inhibiting variant ADH1B reduces the likelihood of alcohol dependence by a factor of between two to nine times, and both heavy and excessive drinking by a factor of about five. The more efficient alcohol breakdown performed by this variant also likely protects the body against drinking binges but may make hangovers worse. Have you ever noticed anyone flushing after drinking a relatively small amount of alcohol? Who was it?

Data on ADH1B has been gathered from around the world. It turns out that the booze-inhibiting variant of this gene is distributed rather nonrandomly. The hottest spot is in southeastern China, with a weak second hot spot in the Middle East. In southeastern China, the frequency of the booze-inhibiting gene goes as high as 99%, with several populations in the 70% to 90% range. In the Middle East, the rates are more in the 30% to 40% range.

Bing Su and his colleagues have brought these findings together with archeological data on the origins of rice agriculture in East Asia—the transition from hunting and gathering to agriculture. The earlier rice agriculture started in a region, the higher the frequency of the booze-inhibiting variant of ADH1B in the populations now inhabiting those regions. Knowing the date at which rice agriculture began then allowed them to account for 50% of the variation in this gene’s frequencies in Asian populations, which is amazingly high given the uncertainty in archaeological dates and all the other factors at work on these populations over thousands of years.

Okay, fine, but what’s the link from agriculture to alcohol? Well, broadly speaking, agriculture and the making of fermented beverages go together. Most hunter-gatherer populations do not have the means, know-how, or resources (e.g., cereals) to make beer, wine, or spirits. Yet agricultural populations usually do, even small-scale, semi-nomadic, slash-and-burn agriculturalists.

In China, the first alcoholic beverages date back almost to the very origins of rice agriculture, along the Yellow River. About 9000 years ago in the ancient farming village of Jaihu, chemical analyses indicate that someone had stored away thirteen pottery jars of a fermented rice-based beverage that probably also contained honey and fruit. It seems that as soon as people domesticated rice, they quickly figured out how to make rice wine. Based on other historical episodes, this probably created alcohol-related problems for rice farmers, which favored any ADH variants that make drinking less fun. Without the cultural evolution of, first, rice agriculture and, second, rice wine, there might be no booze-inhibiting variant of ADH1B.”—Joseph Henrich, The Secret of Our Success: How Culture Is Driving Human Evolution, Domesticating Our Species, and Making Us Smarter (2017)