After studying the genetic material of people who lived in the Bronze Age, scientists saw that the ability to digest milk as adults spread rapidly throughout Europe.
The ability to digest lactose sugar present in milk is a recent development in human evolution – and has contributed considerably to changing not only our eating habits, but to ensuring the survival of the species.
It happened very quickly
But when exactly did humans develop lactose tolerance? This is what researchers from institutions in the United States and Europe investigated in a study recently published in the journal Current Biology.
By analyzing the genetic material of the bones of people who died in the Bronze Age, scientists realized that lactose tolerance spread rapidly throughout Europe, in just a few hundred years – an extremely fast pace compared to other evolutionary changes.
The bones belonged to people who fought in battles on the banks of the Tollense River, which flows through present-day Germany.
These battles were the largest in Europe during the Bronze Age and it is estimated that 4,000 warriors participated, with almost a quarter killed in combat.
Although the materials are more than 3,000 years old, the researchers managed to sequence the DNA of some bone fragments.
The lactase-persistent allele
The experts analyzed the genetic ancestry of the warriors and compared them with modern and ancient populations.
The focus of the study was specifically the lactase-persistent allele, responsible for the production of the lactase enzyme in adulthood, the enzyme that digests milk.
The researchers investigated the presence of this allele in modern and ancient humans, especially medieval Europeans.
That’s because most of the people who acquired the mutation were those who lived in Central and Northern Europe.
They found that only one in eight Bronze Age warriors had the genetic variant that allowed lactose digestion – even though the battles took place more than 4,000 years after the introduction of agriculture in Europe, which would already involve the consumption of some dairy products. But that would soon change.
“When we look at other European genetic data from the early Medieval period less than 2,000 years later, we find that more than 60 percent of individuals had the ability to drink milk as adults,” said Krishna Veeramah, Ph.D., from Stony Brook University, who was part of the research team.
According to Veeramah, this is close to what is observed today in Central European countries, where this index varies from 70% to 90%.
Lactose-tolerant adults were more likely to have children
“It appears that by simply possessing this one genetic change, past European individuals with the ability to digest lactose had a six percent greater chance of producing children than those who could not,” Veeramah added.
But, according to the research leader, Joachim Burger, it is still unclear why this ability was so important in terms of evolution. Some theories may provide the answer.
“With milk being a high-energy, relatively uncontaminated drink, its ingestion may have provided greater chances of survival during food shortages or when supplies of drinking water may have been contaminated,” said Burger, who is a professor at Johannes Gutenberg University Mainz, in Germany.