People who could tolerate milk, according to this theory, gained a new source of calories and protein and passed on their genes to healthier offspring than those without the genetic trait – known as lactase persistence – that their permission to digest milk sugar until adulthood.
But a new study has offered a radically different theory, claiming that side effects such as gas, bloating and intestinal cramps alone weren’t enough to move the evolutionary needle on the genetic mutation.
“Prehistoric peoples in Europe may have started consuming milk from domestic animals thousands of years before they evolved the gene to digest it,” the study authors said.
The study, published in the journal Nature, was carried out in collaboration with more than 100 scientists in various fields, including genetics, archeology and epidemiology. Scientists have mapped the estimated milk consumption in Europe from around 9,000 years ago to 500 years ago.
By analyzing animal fat residues in pottery from hundreds of archaeological sites, as well as DNA samples taken from ancient skeletons, the researchers concluded that lactase persistence was not common until around 1,000 BC. JC, nearly 4,000 years after its first detection.
And, rather than in times of plenty, they argue that it was during famine and epidemics that the mutation became essential for survival: when undigested lactose could lead to severe intestinal disease and death.
Using archaeological records to identify periods when populations declined, they concluded that people were more likely to drink milk when all other food sources had been exhausted, and that during these times diarrhea was more likely. to go from a benign state to a fatal state.
George Davey Smith, an epidemiologist at the University of Bristol who partnered with researchers on an analysis of contemporary data on the persistence of milk and lactase in current populations, said the study raises “intriguing questions on whether some people who believe they are lactose intolerant “could actually be fine 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 US Department of Agriculture’s dietary guidelines recommended so many dairy products – suggesting the federal agency was looking out for the interests of the meat and produce industries. dairy rather than the health of Americans.
USDA dietary guidelines are driven by milk marketing concerns – not nutrition – lawsuit says
Previous studies have suggested that populations must have relied heavily on dairy products before individuals adapted to tolerate them in abundance. A smaller study in 2014 found that the variation that allows humans to digest lactose only appeared in Hungarian DNA samples 3,000 years ago, when it could have appeared 7,000 years ago. years in places like Ireland where cheese making has become abundant.
Amber Milan, a dairy intolerance expert 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 “strong theory” and “supported by previous research on the drivers of genetic selection”. .”
She added, however, that she’s not sure the new study “entirely rules out that widespread milk consumption was the evolutionary force in lactose tolerance” – in part because the genetic data was collected from of Biobank, a UK biomedical database of genetic and health information of some 500,000 people.
The authors also focused on the major European genetic variant for lactase persistence — which, while appropriate for this study, “potentially lacks other genetic variants that drive lactase persistence,” Milan said.