This theory suggests that people who could tolerate milk gained 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 allows them to To digest the sugar present in milk into adulthood.
But a new study offered a radically different theory, arguing that side effects like gas, bloating and intestinal cramps weren’t enough on their own to move the evolutionary needle on the genetic mutation.
“Prehistoric people in Europe may have started consuming milk from domestic animals thousands of years ago before they developed the gene to digest it,” the study authors said.
The study published in the journal temper natureIt was produced in collaboration with more than 100 scientists in a range of fields including genetics, archaeology, and epidemiology. Scientists have determined the estimated milk consumption in Europe from about 9,000 years ago to 500 years ago.
By analyzing remains of animal fat in pottery from hundreds of archaeological sites, along with DNA samples taken from ancient skeletons, researchers have concluded that lactase persistence was not common until around 1000 B.C., roughly 4,000 years after it was first discovered.
Rather than times of plenty, they argue, during famine and epidemics the presence of the mutation became critical to survival: when undigested lactose can lead to serious intestinal disease and death.
Using archaeological records to identify periods when the population was declining, they concluded that people were more likely to drink milk when all other food sources had been exhausted, and that during those periods, diarrhea was more likely to escalate from a mild to a fatal state.
George Davy Smith, an epidemiologist at the University of Bristol, who collaborated with researchers to analyze contemporary data on milk and lactase sustainability in current populations, said the study raises “fascinating questions” about whether some people who think they are lactose intolerant “may be lactose intolerant.” It’s actually a good thing if they drink milk.”
About a quarter of Americans are lactose intolerant. in A lawsuit was filed last yeara group of American doctors questioned why the USDA Dietary Guidelines recommend so much dairy — suggesting that the federal agency cares about the interests of the meat and dairy industries rather than the health of Americans.
Previous studies indicated that the population had to rely heavily on dairy products before individuals adapted to tolerate them in abundance. Smaller study in 2014 It 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 7,000 years ago in places like Ireland where cheesemaking became abundant.
Amber Milan, an expert in dairy intolerance at the University of Auckland, said the idea that the lactase mutation only became important for survival when Europeans began to endure epidemics and famines is a “sound theory” and “supported by previous research into the drivers of genetic selection”. “
She added, however, that she was not sure that the new study “completely rules out that widespread milk consumption was 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. of about 500,000 people.
The authors also focused on the major European genetic variant for lactase persistence—which, while appropriate for this study, “is likely to be missing other genetic variants that lead to lactase persistence,” Millan said.