Ancient milk-drinkers were just fine with their lactose intolerance–until famine struck

Only infants would have had the digestive capacity to process lactose, one of the major sugars in milk, 11,700 years ago, at the conclusion of the last Ice Age. It is a recent development in human evolution to be able to do so into maturity. People of European, South Asian, Middle Eastern, and West African heritage are most likely to exhibit it, and it evolved so swiftly that it serves as the archetypal illustration of how humans have adapted to agriculture.

However, new study revealed this week in the journal Nature indicates that prehistoric humans in Europe ingested lactose despite not being able to digest it. Adults didn't hold on to lactase, the essential enzyme that breaks down the sugar, until poverty and sickness transformed lactose become a liability.

According to research co-author Richard Evershed, an archaeologist and paleochemist at the University of Bristol, "what we've proved is the established wisdom is incorrect." The conventional wisdom is that the few fortunate milk drinkers benefited in some way from the beverage—possibly allowing them to develop more quickly or providing them with more vitamin D in the gloomy Northern latitudes—which encouraged the spread of lactase-processing genes.

Given how quickly Europeans acquired lactose tolerance, those lacking it must have been at a significant disadvantage. To put it simply, Evershed adds, "You've had to murder someone to have [that type of] selection."

Three different pieces of evidence are used to build the new milk-drinking narrative. The first is a map made up of around 13,000 pieces of antiquated pottery that have been gathered from Portugal, Turkey, and Finland. Despite the fact that the contents of the pots had long since dried up, animal fats leave specific remains that, 9,000 years later, enable researchers to determine whether they contained milk.

What led farmers who couldn't metabolize lactose to drink milk, then? According to another author and University of Bristol epidemiologist George Davey Smith, the health risks of lactose intolerance are frequently exaggerated. Bloating, flatulence, and other alleged lactose intolerance symptoms are less frequent than most people believe. Undigested lactose can also result in diarrhea, as can coffee, prunes, and a variety of other delicious foods.

The researchers discovered that well over 90% of persons who are unable to metabolize lactose nevertheless consume cow's milk using the 500,000-person genetic database UK Biobank. It turns out that your capacity to tolerate lactose just isn't a significant determinant of your ability to tolerate cow juice. One of my co-authors only performed a lactose test during the experiment, according to Evershed. She had been drinking milk until she discovered that she was lactose intolerant. She made no reference to it. Those with modified gut biomes can still digest lactase even when they don't normally make it. Some people have an allergy to one component of milk yet develop the enzyme needed to digest the sugar.

Davey Smith notes that it "became obvious that individuals could cheerfully drink milk," enzyme or not.

But if milk is so easily absorbed, it raises another question: If they didn't require lactose tolerance, why would ancient Europeans have done it so quickly?

Understanding what occurs when things are difficult is the key. A little wad of extra milk sugar forms in the colon of a person who cannot digest it. According to Davey Smith, undigested lactose can occasionally cause diarrhea by "kind of sucking water out." That's not usually an issue, but lactose feces can make someone ill if they are undernourished or suffering from an intestinal condition.

On a community level, milk might transform from a source of calories into a type of poison amid illness epidemics or famines. According to the genes found in the bones of ancient Europeans, the capacity to fend off such poisoning is what gave rise to lactose tolerance in the region.

Heat stress might cause the dairy business to go under.

The researchers discovered that humans who drank milk experienced no evolutionary pressure to digest lactose by aligning the map of ancient milk-vessels, the existence of the enzyme in ancient genes, and the frequency of ancient bones. According to Mark Thomas, a research co-author and specialist in human evolution at University College London, "this pulls the rug out from under the feet of just about every argument for why that natural selection was there." "Milk consumption explains nothing."

The strongest explanation for variations in lactase persistence was evolutionary pressure during population collapses. Thomas asserts that "such population decreases almost probably point to famines." Famines would also have had a double impact. Ancient farmers would have consumed all of their low-lactose yogurts and cheeses first during times of food scarcity. When crops fail, Thomas predicts that "fresh milk will be the only option left for them." When severe malnutrition is combined with high-lactose diets, diarrhea becomes more than just a nuisance; it becomes lethal.

A portion of the push towards lactase persistence was also explained by dense populations, as shown by the distribution of skeletal remains. According to the researchers, this occurred when children—who were still young but too old to make lactase—were exposed to the risk of intestinal infectious illnesses and lactose diarrhea, both of which flourished in close quarters. The interaction of these factors primarily explains why lactase persistence was so widespread by the beginning of the Iron Age, or around 3,000 years ago.

According to Davey Smith, the timing also defies the assumption that the introduction of agriculture, some 10,000 years ago, made people sicker and hungry. "I believed we'd uncover anything that fits in with the timeline, which claims that agriculture is the biggest error mankind have ever done. As it turned out, 5,000 years had passed.