Due to frequent famines and disease outbreaks, ancient Europeans may have developed the capacity to digest milk. Researchers report on July 27 in Nature that the first groups of dairy farmers arrived in the southeastern part of Europe some 9,000 years ago. Researchers claim it took a few thousand years for a trait for processing lactose, to emerge in high numbers among Europeans.
These findings, which are supported by DNA data and samples of animal fat residue from hundreds of archaeological sites, challenge the widely held belief that the nutritional and health benefits of milk led to the evolution of lactose tolerance. This theory was proposed by biogeochemist Richard Evershed of the University of Bristol in England and peers.
Those who consume milk yet have lactose intolerance often endure gastrointestinal distress. Evershed’s team argues that such bothersome responses weren’t severe enough to push the evolutionary line towards lactose tolerance. Lactose-induced diarrhea was previously thought to to be dangerous for very malnourished people in agricultural communities, but recent scientific research suggests that it may have been lethal during periods of repeated famines and infectious disease epidemics. They argue that repeated dangers “hotwired” the development of lactose tolerance.
In the words of bioarchaeologist Oliver Craig of the University of York in England, the analysis fully rules out widespread milk intake as the evolutionary impetus underlying lactose tolerance. Additional study is needed to determine the scope of any famines or epidemics that may have affected the ancient Europeans’ ability to digest milk. Researchers should also be aware that low-lactose dairy products like cheese have been present since at least 7,400 years ago in Europe.
It is puzzling that lactose-intolerant Europeans could not have fared better in times of hunger or sickness if these foods had been more commonly accessible to them.
By reviewing previously published data on animal fat residues collected from over 13,000 ceramic shards at around 550 archaeological sites, Evershed’s team created a map of the projected milk consumption patterns throughout Europe between 9,000 and 500 years ago.
Farmers who migrated to the Balkan Peninsula in southeastern Europe at the start of that time period brought dairying there, and locals quickly adopted the practice of drinking milk on a daily basis. The consumption of milk then changed significantly through time in various sections of the continent. Western France, Northern Europe, and the British Isles all had high rates of milk consumption around 7,500 years ago. Central Europe was less likely to have a dairy industry.
Gene variant boosting the activity of lactase
Using data on ancient DNA that was released and collected from close to 1,800 people in Europe and Asia, Evershed’s team was also able to trace the origin and progression of the primary gene that is responsible for lactose tolerance. According to the researchers, the first evidence of a gene variation in adults in Europe that is responsible for enhancing the function of lactase, an enzyme that gives resistance by chemically disintegrating lactose, goes back to around 6,650 years ago. This version of the gene was found in Europe. According to their findings, however, the genetic feature known as lactase persistence did not become prevalent in Europe until around 3,000 years ago.
According to the findings of the researchers, prior to that time period, rising levels of lactase persistence were often correlated with population declines that were caused by famines in certain places. According to the researchers, unearthed agricultural sites throughout Europe show traces of recurrent population losses that were impacted by severe food scarcity around 8,000 and 4,000 years ago. These population declines occurred during the time periods of 4,000 and 8,000.
Assessments of settlement density, which reflect how tightly together humans lived, also had a tendency to decrease during periods of rising lactase persistence. This is because settlement density is a statistical measure of how close together people dwell. The scientists believe that the proliferation of animal-borne diseases such as salmonella led to a reduction in settlement density. This occurred because inhabitants who were unable to digest lactose experienced an increased number of fatalities. Evershed’s group hypothesizes that during such times of poor nutrition and sickness, increased levels of lactase persistence increased access to nutrients in milk that were urgently required.