Just 5,000 years ago, even though it was a part of their diet, virtually no adult humans could properly digest milk. But in the blink of an evolutionary eye northern Europeans began inheriting a genetic mutation that enabled them to do so. The trait became common in just a few thousand years, and today it’s found in up to 95 percent of the population.
In a study published [July 22] in Nature, researchers compared archaeological evidence for 9,000 years of European milk use with genetics, and found an unusually rapid, evolution of lactose tolerance among Europeans well after they first started consuming the beverage. The authors suggest that something more extreme than regular milk consumption drove the genetic change. Exceptional stressors like famines and pathogens may have exacerbated milk’s typically mild gastrointestinal effects on the lactose intolerant, creating deadly bouts of diarrhea and dehydration while making the ability to digest milk extra valuable.
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“It rewrites the textbooks on why drinking milk was an advantage,” says lead author Richard Evershed, director of the Biogeochemistry Research Center at the University of Bristol. “In order to evolve a genetic mutation so quickly, something has to kill off the people that don’t carry it.”
