Famine and disease drove the evolution of lactose tolerance in Europe
Prehistoric people in Europe were consuming milk thousands of years before humans evolved the genetic trait allowing us to digest the milk sugar lactose as adults, finds a new study. The research, published in Nature, mapped pre-historic patterns of milk use over the last 9,000 years, offering new insights into milk consumption and the evolution of lactose tolerance.
Until now, it was widely assumed that lactose tolerance emerged because it allowed people to consume more milk and dairy products. But this new research, led by scientists from the University of Bristol and University College London (UCL) alongside collaborators from 20 other countries, shows that famine and exposure to infectious disease best explains the evolution of our ability to consume milk and other non-fermented dairy products.
While most European adults today can drink milk without discomfort, two thirds of adults in the world today, and almost all adults 5,000 years ago, can face problems if they drink too much milk. This is because milk contains lactose, and if we don’t digest this unique sugar, it will travel to our large intestine where it can cause cramps, diarrhea, and flatulence; known as lactose intolerance. However, this new research suggests that in the UK today these effects are rare.
Professor George Davey Smith, Director of the MRC Integrative Epidemiology Unit at the University of Bristol and a co-author of the study, said: “To digest lactose we need to produce the enzyme lactase in our gut. Almost all babies produce lactase, but in the majority of people globally that production declines rapidly between weaning and adolescence. However, a genetic trait called lactase persistence has evolved multiple times over the last 10,000 years and spread in various milk-drinking populations in Europe, central and southern Asia, the Middle East and Africa. Today, around one third of adults in the world are lactase persistent.”
By mapping patterns of milk use over the last 9,000 years, probing the UK Biobank, and combining ancient DNA, radiocarbon, and archaeological data using new computer modelling techniques, the team were able to show that lactase persistence genetic trait was not common until around 1,000 BC, nearly 4,000 years after it was first detected around 4,700-4,600 BC.
“The lactase persistence genetic variant was pushed to high frequency by some sort of turbocharged natural selection. The problem is, such strong natural selection is hard to explain,” added Professor Mark Thomas, Professor of Evolutionary Genetics and study co-author from University College London.
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