People who could tolerate milk, according to this theory, had a new source of calories and protein and passed on their genes to healthier offspring than people who did not have the genetic trait – which allows them – lactase resistance. absorption of sugar in milk during adulthood.
But a new study suggests a radically different theory, arguing that side effects like gas, bloating and cramping aren’t enough on their own to move the evolutionary needle on genetic mutation.
“Prehistoric humans in Europe began consuming milk from domesticated animals thousands of years before the genes for digesting milk appeared,” say the study’s authors.
The study, published in the journal Nature, was prepared in collaboration with more than 100 scientists in a number of fields, including genetics, archeology and epidemiology. Scientists have mapped estimated milk consumption in Europe from about 9,000 years ago to 500 years ago.
Researchers analyzed animal fat residues on pottery from hundreds of archaeological sites, along with DNA samples from ancient skeletons, and concluded that lactase resistance was widespread by 1000 BC, nearly 4,000 years after it was first identified.
And they say that having the mutation became essential to survival during famines and epidemics, not during times of plenty: undigested lactose can cause serious intestinal disease and death.
Using the archaeological record to identify periods of population decline, they concluded that when all other food sources were depleted, people drank more milk and that diarrhea was more likely to progress from mild to fatal.
Epidemiologist George Davey Smith of the University of Bristol, who collaborated with the researchers to analyze modern data on milk and lactase resistance in current populations, said the study raises “interesting questions” about whether or not certain people are lactose intolerant. impatient “it would be better to drink milk”.
About a quarter of Americans are lactose intolerant. In a lawsuit filed last year, a group of U.S. doctors questioned why the U.S. Department of Agriculture’s dietary guidelines recommend so much dairy — arguing that the federal agency is serving the interests of the meat and dairy industry rather than the health of Americans.
USDA dietary guidelines are driven by dairy marketing issues, not nutrition
Previous studies have suggested that populations should rely heavily on dairy products. A smaller study in 2014 found that the variation that allows for lactose digestion did not appear in Hungarian DNA samples until 3,000 years ago, and in places like Ireland where cheese-making was abundant, it may have appeared as early as 7,000 years ago.
Amber Milan, an expert on dairy intolerance at the University of Auckland, said the idea that the lactase mutation became essential for survival only when Europeans began to experience epidemics and famines was a “good theory” and “supported by previous studies of drivers of genetic selection”. ” .”
He added that the new study “completely rules out that widespread dairy consumption is an evolutionary force in lactose tolerance” – partly because the genetic data was collected from the British biomedical database of genetic and health information Biobank. From adding 500,000 people.
The authors also focused on a major European genetic variant for lactase resistance — which, while suitable for the study, “might miss other genetic variants that cause lactase resistance,” Milan said.