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A group of scientists have concluded that ancient Europeans drank milk for millennia despite the digestive problems it may have caused, casting doubt on theories of how humans evolved to tolerate it.
Scientists have long speculated that the enzyme needed to avoid gastrointestinal discomfort evolved rapidly in populations where domestication of dairy animals was prevalent.
According to this theory, people who could tolerate milk got a new source of calories and protein and passed their genes on to healthier offspring than those without the genetic trait – known as lactase persistence – that allowed them to for the absorption of sugar in milk in adulthood.
But a new study offers a radically different theory, arguing that side effects like gas, bloating and intestinal cramps aren’t enough on their own to move the evolutionary needle on genetic mutation.
“Prehistoric humans in Europe may have started consuming milk from domesticated animals thousands of years before they developed the gene to digest it,” the study authors said.
The study, published in the journal Nature, was done in collaboration with more than 100 scientists in various fields, including genetics, archeology and epidemiology. Scientists have mapped the approximate consumption of milk in Europe from about 9,000 years ago to 500 years ago.
By analyzing animal fat residues in pottery from hundreds of archaeological sites, along with DNA samples collected from ancient skeletons, the researchers concluded that lactase resistance was not common until around 1000 BC. nearly 4,000 years after it was first discovered.
And instead of times of plenty, they argue, it was during times of famine and epidemics that the presence of the mutation became critical for survival: when undigested lactose could lead to serious intestinal disease and death.
Using the archaeological record to identify periods when populations shrank, they concluded that people were more likely to drink milk when all other food sources were exhausted, and that during these periods diarrhea was more likely to escalate from a mild to fatal condition.
George Davey Smith, an epidemiologist at the University of Bristol who partnered with the researchers in analyzing contemporary data on milk and lactase persistence in current populations, said the study raises “fascinating questions” about whether some people who believe they are lactose intolerance “it might actually be okay if they drank milk.”
About a quarter of Americans are lactose intolerant. In a lawsuit filed last year, a group of American doctors questioned why the USDA’s dietary guidelines recommend so much dairy — suggesting the federal agency is looking out for the interests of the meat and dairy industry rather than the health of Americans.
USDA Dietary Guidelines Driven by Milk Marketing Concerns, Not Nutrition, Lawsuit Claims
Previous studies have shown that populations must rely heavily on dairy products before humans can adapt to tolerate them in abundance. A smaller study in 2014 found that the variation that allows humans to digest lactose did not appear in Hungarian DNA samples until 3,000 years ago, while it may have appeared as early as 7,000 years ago in places like Ireland, where cheese production is abundant.
Amber Millan, a dairy intolerance expert at Oakland University, said the idea that the lactase mutation only became important for survival when Europeans began to endure epidemics and famines was a “sound theory” and “supported by previous research of the engines of genetic selection.”
However, she added that she was not sure the new study “completely rules out that widespread milk consumption is the evolutionary force behind lactose tolerance” – in part because the genetic data was collected from Biobank, a British biomedical database of genetic and health information from around 500,000 people.
The authors also focused on the major European genetic variant for lactase persistence — which, while relevant for this study, “potentially misses other genetic variants that lead to lactase persistence,” Milan said.
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