The prehistoric peoples of Europe they drank milk thousands of years ago develop the genetic adaptation that allows adults digest lactosea trait that evolved not so they could take in more dairy, but would have been related to famines and infectious diseases.

A study that publishes Nature led by the University of Bristol and University College London (UK), with Spanish participation, it has mapped milk consumption patterns over the past 9,000 years.

To do this, they analyzed animal fat residues in ceramic fragments from 554 archaeological sites, including the Portalón de Cueva Mayor in Atapuerca (Burgos, northern Spain), and analyzed the DNA of ancient and modern individuals to understand how it emerged and evolved. tolerance.

Humans drank milk as early as the Neolithic, although its consumption varied by region and time, although almost all adults were intolerant to its sugar, lactose.

A missing genetic trait

Mammals in their infancy can digest lactose using an enzyme called lactase, but when they become adults most of them stop producing it, however, a mutation in DNA allows for the persistence of lactase.

Analysis of DNA data from prehistoric Eurasian individuals over time indicates that this genetic trait was not common until around 1000 BC, which is nearly 4000 years after it was first detected, around 4700–4600 BC.

The persistence of lactase was a genetic trait absent in the Neolithic and the Caolithicwhich spread during the Bronze Age, becoming more and more common to this day.

It is surprising that despite having domesticated goats, sheep, cows or camels for so long and consumed milk and its derivatives, genetic adaptation was not established until several millennia later and very quickly, José Miguel Carretero told Efe. . Evolution of the Spanish University of Burgos and signatory of the study.

The genetic changes that favored lactase persistence are one of the most influential and fastest-evolving genetic adaptations in human populations over the past 10,000 years, the researchers write.

Until now it was thought that lactose tolerance was born because it allowed you to consume more milk and dairy products, but this new research tells a different story.

Famine and exposure to zoonotic pathogens are the factors that “explain best” the evolution of lactose tolerancesince modeling of genetic and archaeological data did not show a strong relationship between drinking milk and increased persistence of lactase.

They also analyzed data from current Europeans taken from the British biobank to see the relationship between milk consumption and health, Carretero said.

The result was that their consumption “Does not bring advantages” in lactose-tolerant people than others, explains the anthropologist and project member Atapuerca, there had to be “other reasons that made people with persistent lactase more common”.

Consumption prolonged in 9 thousand years

The consumption of milk in Europe had been widespread for at least 9,000 years and healthy people, even intolerant ones, could drink it without too much trouble, although it can cause cramps, flatulence or diarrhea.

However, in situations of famine, when a crop fails or livestock is dwindling, the consumption of raw or slightly fermented milk is more mandatoryCarter said.

At that time the non-tolerant people were at a disadvantage, because if you are malnourished, weakened, and – he stressed – you also have diarrhea from drinking a lot of raw milk, then you have problems that endanger your life.

Something similar would happen in times of pandemics, which “require high population densities for the proliferation of the pathogen.” From the Neolithic they began to form large inhabited centerswhere the space was also shared with pets.

Therefore, in times of famine, infectious epidemics or both, the high consumption of raw milk, almost out of necessity, would have made the death of lactose intolerant more likely before or during reproductive age, which would increase the demographic frequency of persistence. of the lactase gene at current levels.

The team led by Mark Thomas of University College London introduced indicators of past famines and exposure to pathogens in a new statistical method, and the results supported this theory.

To delve into the co-evolution of dairy farming and the persistence of lactase, the team led by Richard Evershed of the University of Bristol created a comprehensive map of prehistoric milk consumption. analyzing the residues of animal fat from 13,181 ceramic fragments.

The researcher of the Spanish University of Burgos, Marta Francés, who participated in the analyzes, explained that she had identified the lipids that are generally stored inside the ceramic, which are searched for through chemical processes.

The “easiest” to identify are of terrestrial animal origin and, in general, it is possible to know which groups of animals they belong to, for example ruminants or non-ruminants, although – he specified – they cannot be separated by species.

EFE