According to a new study, prehistoric people in Europe consumed milk thousands of years before humans developed the genetic trait that enables us to digest the milk sugar lactose as adults.
In order to gain new knowledge about milk consumption and the development of lactose tolerance, the study-which was published in Nature-mapped prehistoric patterns of milk consumption over the previous 9,000 years.
Lactose tolerance in Europe
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It was previously believed that the development of lactose tolerance resulted from the ability to consume more milk and dairy products, as per ScienceDaily.
But according to a recent study led by researchers from the Universities of Bristol and London's University College (UCL) and involving participants from 20 other nations, famine and contact with infectious diseases best account for how our capacity to consume milk and other non-fermented dairy products evolved.
While the majority of adults in Europe today can consume milk without feeling any distress, two-thirds of adults worldwide today, and nearly all adults 5,000 years ago, can experience problems from excessive milk consumption.
This is due to the fact that milk contains lactose, a special sugar that, if we are lactose intolerant, will pass through our large intestine and cause cramps, diarrhea, and flatulence. However, according to this new study, these effects are not common in the UK.
We must produce the enzyme lactase in our guts in order to digest lactose, according to Professor George Davey Smith, Director of the MRC Integrative Epidemiology Unit at the University of Bristol and a co-author of the study.
Lactase is almost universally produced in newborns, between weaning and adolescence, it rapidly declines in most of the world's population.
But over the past 10,000 years, a genetic characteristic known as lactase persistence has undergone numerous evolutionary changes and spread to numerous milk-drinking populations in Europe, central and southern Asia, the Middle East, and Africa. Approximately one-third of adults worldwide today have lactase persistence.
The team was able to demonstrate that lactase persistence genetic trait was not widespread until roughly 1,000 BC, nearly 4,000 years after it was first discovered around 4,700-4,600 BC, by mapping patterns of milk use over the previous 9,000 years, exploring the UK Biobank, and incorporating ancient DNA, radiocarbon, and archaeological data using new computer modeling techniques, as per Technology Networks.
Some turbocharged natural selection drove the genetic variant for lactase persistence to high frequency. Professor Mark Thomas, Professor of Evolutionary Genetics and study co-author from University College London, said that the difficulty in explaining such powerful genetic selection.
Professor Richard Evershed, the study's principal investigator from the School of Chemistry at the University of Bristol, created an unprecedented database of nearly 7,000 organic animal fat residues from 13,181 pieces of pottery from 554 archaeological sites to determine where and when people were consuming milk.
According to his research, milk consumption in prehistoric Europe peaked around 9,000 years ago and fluctuated between being high and low depending on the region.
The UCL team, led by Professor Mark Thomas, used published ancient DNA sequences from more than 1,700 ancient European and Asian individuals to compile a database of the presence or absence of the lactase persistence genetic variant in order to understand how this relates to the evolution of lactase persistence.
It was after about 5,000 years that they first noticed it. It was occurring at noticeable frequencies 3,000 years ago and is still very widespread today. The study's authors came to the following conclusion: As population numbers and settlement sizes continued to increase in later prehistory, poor sanitation and an increase in diarrheal diseases, particularly those of an animal origin, would have had a greater negative impact on human health. Consuming milk under these circumstances would have increased mortality rates, with those lacking lactase persistence being particularly at risk.
Under famine conditions, when disease and malnutrition rates rise, this situation would have become even worse. This would increase the prevalence of lactase persistence in the population because people without a version of the lactase persistence gene variant will be more likely to pass away before or during their reproductive years.
