Evolution of the "milk" gene
Europeans learned to drink milk unexpectedly late and quickly
Such conclusions were prompted by the analysis of the supposedly first military clash in the history of Europe
The study of the genomes of several dozen soldiers who died in the north of Germany 3.2 thousand years ago during a large–scale and bloody battle showed that almost all of them could not digest lactose - one of the most important components of milk. This suggests that their descendants "learned" this unexpectedly late, but very quickly. The results of the study were published by the scientific journal Current Biology (Burger et al., Low Prevalence of Lactase Persistence in Bronze Age Europe Indicates Ongoing Strong Selection over the Last 3,000 Years).
"If you look at the genomes of the inhabitants of medieval Europe, who lived only a couple of thousand years later, you can see that more than 60% were able to digest lactose. This suggests that this mutation has spread through the population unusually quickly. In the language of mathematics, its speakers were 6% more likely to leave descendants than other Europeans. This is the clearest evidence that natural selection is acting on us," said one of the authors of the study, associate professor at the State University of New York at Stony Brook (USA) Krishna Virama.
Scientists suggest that dairy cattle breeding originated in the Middle East and India from 10 to 15 thousand years ago, that is, at about the same time when agriculture arose and people switched to a sedentary lifestyle. The domestication of cows led to the fact that a mutation in the LCT gene appeared in the populations of the first farmers of the Earth.
Thanks to her, people have an opportunity that almost all other mammals are deprived of – the opportunity to assimilate lactose – sugar, which is a lot in milk, in adulthood. Now most Europeans have this mutation, despite the fact that other inhabitants of the Earth do not have it as often.
In recent years, scientists have been trying to understand how it spread through the populations of ancient people. Thus, researchers are trying to find out when residents of different regions of Europe and other parts of the world started drinking milk and why they started doing it. Thanks to such studies, many paleogeneticists assume that Europeans acquired this ability relatively recently – about 5-6 thousand years ago. It was then that the first Indo-Europeans entered Europe.
In the latest study, Virama and his colleagues analyzed the genomes of 14 soldiers who died in what is believed to be the first major military clash in the history of Europe. It happened about 3.2 thousand years ago. As a result, geneticists found out that very few of those who lived in Europe at that time could digest lactose.
Traces of this conflict were discovered by one of the authors of the article, Professor Thomas Terberger. He conducted excavations on the banks of the Tollense River, 120 km from Berlin. Here, back in 1996, an amateur archaeologist found an unusually large burial of people who lived at the end of the Bronze Age.
Continuing the work, Terberger and his colleagues found out that a major battle took place on the riverbank, in which more than four thousand soldiers participated. A quarter of them died. During six years of excavations, scientists have found the remains of five horses and more than a hundred warriors, as well as many artifacts, including stone and bronze weapons.
Scientists tried to find out how close the participants of this massacre were to each other. To do this, they studied scraps of DNA from the bones of dead soldiers. Thus, they recovered 14 relatively complete genomes of the dead men and confirmed that they all came from the same tribe or population. Thanks to this, Virama, Terberger and their colleagues studied how often a mutant version of the LCT gene was found in the DNA of these ancient inhabitants of Europe.
It turned out that only every eighth warrior who died in the battle on the Tollense River could digest lactose. This was a big surprise for scientists for two reasons at once. On the one hand, they did not expect that a mutation in this gene would occur so rarely in the inhabitants of ancient Germany, although about four thousand years have passed since the appearance of the first farming communities in Europe.
On the other hand, this suggests that over the next 3.2 thousand years, this variation of the gene spread very quickly through the population: now it occurs in 90% of modern residents of Northern Germany. In other words, the mutation in the LCT gene turned out to be so beneficial to its carriers that it took a dominant position in just a hundred generations. By the standards of evolution, this is almost instantaneous.
"So far we cannot say why the ability to absorb lactose and other sugars from milk in adulthood was so beneficial for ancient Europeans. Perhaps the ability to drink a clean and at the same time high–calorie drink helped them survive at a time when they had no food or clean water sources," the researchers conclude.
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