A new study shows that prehistoric people in Europe were consuming milk thousands of years ago. New insights into milk consumption and the evolution of Lactose tolerance can be found in the research published in Nature.
Lactose tolerance was thought to have arisen because people were consuming more dairy products. The evolution of our ability to consume dairy products can be explained by famine and exposure to infectious disease.
Almost all adults 5,000 years ago had problems if they drank too much milk, and two-thirds of adults today have the same problem. Lactose is found in milk and if it can't be broken down, it will travel to the large intestine where it can cause a range of health problems. The research shows that these effects are rare in the U.K.
The co-author of the study, Professor George Davey Smith, director of the MRC Integrative Epidemiology Unit at the University of Bristol, said that to digest Lactose we need to produce the lactase in our gut. Almost all babies produce lactase, but in the majority of people, production begins to decline between the ages of 16 and 18. In Europe, central and southern Asia, the Middle East and Africa, lactase persistence has evolved multiple times over the last 10,000 years. Around one third of the world's population are lactase persistent.
The team was able to show that lactase persistence genetic trait was not common until around 1000 BC by combining ancient DNA, radiocarbon, and archaeological data.
Natural selection pushed the lactase persistence genetic variant to high frequencies. Professor Mark Thomas is a professor of Evolutionary Genetics and study co-author from University College London.
Professor Richard Evershed, the study's lead from Bristol's School of Chemistry, assembled an unprecedented database of nearly 7,000 organic animal fat residues from 13,181 fragments of pottery to find out where and when people were consuming milk. Milk was used extensively in European prehistory, but increased and decreased in different regions at different times.
Professor Mark Thomas and his team at the University College London assembled a database of the presence or absence of the lactase persistence genetic variant from more than 1,700 European and Asian individuals. Around 5000 years ago, they saw it. It was common by 3000 years ago and still is. A new statistical approach was developed by his team to look at how well changes in milk use are explained by lactase persistence. They were able to show they could detect a relationship if it existed, but they didn't find one.
The U.K. Biobank data, consisting of genetic and medical data for more than 300,000 living individuals, found only minimal differences in milk-drinking behavior between people with and without lactase. The majority of people who were genetically lactase non-persistent had no adverse health effects when they drank milk.
Milk use was widespread in Europe for at least 9000 years, and healthy humans, even those who are not lactase persistent, could happily consume milk. Drinking milk in lactase non-persistent individuals can lead to a high concentration of lactose in the gut, which can lead to fluid in the colon, and dehydration, which can be caused by the combination of the two.
You won't die of it if you drink lots of milk and are healthy. If you have life-threatening problems if you are severely malnourished, then you need to get help. Prehistoric people would have been more likely to drink unfermented high-lactose milk when their crops failed.
Professor Thomas' team used indicators of past famine and pathogen exposure to test their ideas. Natural selection was stronger when there were more famine and more pathogens.
As populations and settlement sizes grew, their impact on human health would have been more pronounced. Milk consumption would cause death rates to increase, with people who lack lactase persistence being particularly vulnerable. The situation would have gotten worse under famine conditions. People who don't have a copy of the lactase persistence gene variant are more likely to die before or during their reproductive years.
The same factors that influence human mortality today drove the evolution of this amazinggene through prehistory.
More information: Richard Evershed, Dairying, diseases and the evolution of lactase persistence in Europe, Nature (2022). DOI: 10.1038/s41586-022-05010-7. www.nature.com/articles/s41586-022-05010-7 Journal information: Nature
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