In a study published [July 27] 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.

The team put these ideas to a test using models which suggested that the gene variant for lactase persistence did increase in populations when they were impacted by famine or pathogens.

The environmental stressors that drove lactose tolerance could have worked in tandem, and they might have been very different during each of the five different times it is known to have evolved in Europe, the Middle East and Africa.

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[Dr. Shevan] Wilkin adds that scientists have been floating various ideas to explain the mysteries of milk digestion, including how lactose tolerance evolved so late and so quickly, and why heavy milk consumers like the steppe dwellers remain lactose intolerant. Now, she says, a framework exists that can further investigate those questions.

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