Have you ever wondered why some adults can digest milk while others can’t? A special protein called lactase enables milk digestion in early childhood. This lactase protein usually disappears in adult humans along with the ability to digest milk. However, there is a gene version, or allele, that enables the persistence of lactase in one-third of adults. Lactase persistence (LP) began to increase in human populations around 3,000 years ago. What were the evolutionary influences that caused this increase in LP?

 A long-standing hypothesis suggests that LP increased with an increase in milk consumption.  However, researchers from the University of Bristol have provided evidence against this hypothesis. The scientists created a detailed historical map of European milk consumption by analyzing ancient pot fragments for traces of milk fat. They compared this map to the frequency of the LP allele in ancient DNA from the same time period to demonstrate that changes in milk consumption do not explain the presence of the allele. By analyzing DNA, health and lifestyle metrics of modern humans, they found that health and fitness benefits of milk could not explain the rise in the LP allele. Instead, they offer support for two alternative explanations suggesting that the ability to digest milk was advantageous specifically in times of famine and increased disease. During these times, LP individuals could consume milk as a great alternative source of calories and hydration. Meanwhile, the symptoms that result from the inability to digest milk, such as diarrhea and dehydration, would have been particularly deleterious in the context of famine or disease.

The authors of this study have provided compelling explanations for the spread of LP in Europe. These results suggest that the ability to digest milk could have helped ancient peoples survive famine and disease. These findings and approaches could be helpful in understanding  the evolution of milk digestion and LP alleles in other populations across the world. 

Richard Evershed is a Professor in the School of Chemistry and Cabot Institute for the Environment Biological and Archaeological Chemistry, Atmospheric and Global Change Chemistry at the University of Bristol. 

Managing Correspondent: Isle Bastille 

Press Articles: “The mystery of early milk consumption in Europe”

Original Articles: “Dairying, diseases and the evolution of lactase persistence in Europe”

Image Credit: https://www.rawpixel.com/search/milk

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