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Famine and disease may have driven ancient Europeans’ lactose tolerance

Ancient Europeans may have evolved an ability to digest milk thanks to periodic famines and disease outbreaks.

Europeans avidly tapped into milk drinking starting around 9,000 years ago, when dairying groups first reached the continent’s southeastern corner, researchers report July 27 in Nature. Yet it took several thousand years before large numbers of Europeans evolved a gene for digesting lactose, the sugar in milk, the investigators say.

These discoveries — based on animal fat residue samples from hundreds of archaeological sites and a trove of DNA data — undermine an influential idea that milk use dramatically increased as the product’s nutritional and health benefits drove the evolution of lactose tolerance, say biogeochemist Richard Evershed of the University of Bristol in England and colleagues.

Milk drinkers who can’t digest lactose experience diarrhea, gas, bloating and intestinal cramps. Those uncomfortable reactions were too mild to move the evolutionary needle toward lactose tolerance on their own, Evershed’s group says. But during periodic famines and infectious disease outbreaks, lactose-induced diarrhea became fatal for severely malnourished individuals in farming communities, the scientists suggest. Those recurring threats hotwired the evolution of lactose tolerance, they contend.

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