More than a quarter of a billion dairy cows help meet the demand for milk around the world . Scientists had long thought that the popularity of milk helped explain the evolution of the genetic trait that allowed many people to digest lactose, the sugar found in milk, in adulthood. However, a new study published in the journal Nature suggests that prehistoric humans in Europe drank milk thousands of years before they developed this trait. These new findings suggest that popularity may not have driven the rise of this variation, but rather famine and disease.
Thus, our ability to enjoy dairy treats today could be due to the sacrifice of our ancestors who succumbed to disease and famine thousands of years ago, according to research by researchers at the University of Bristol and the University College London (UCL).
In times of famine and disease, when people were already weakened, drinking milk could have been fatal for those who were lactose intolerant. As a result, people who carried the gene for lactose tolerance were more likely to survive and pass the gene on to their offspring, increasing its prevalence in society. “When a person is severely malnourished, diarrhea can go from being an inconvenience to a fatal condition,” said Mark Thomas, professor of evolutionary genetics at UCL and co-author of the paper.
Evolution kicks in
The study authors analyzed thousands of animal fat residues found on more than 13,000 pottery shards from 554 archaeological sites across Europe. Microscopic traces of milk on pottery shards suggest that human consumption of milk was, in fact, high in Neolithic Europe from around 7000 BC. C. onwards.
Unexpectedly, genetic evidence from prehistoric European and Asian peoples showed that the gene that codes for lactase production was not common until around 1000 BC. C., almost 4,000 years after it was first detected around 4,700 BC. C. It then spread across the continent like wildfire in a few thousand years.
“This is really quite shocking,” Professor Mark Thomas, an expert in evolutionary genetics and ancient DNA at University College London, told an online news conference. “The frequency of the genetic variant that causes lactase persistence has increased incredibly fast. Ridiculously fast. Inexplicably, almost fast,” he added. “It is probably the most selected single-gene trait that has evolved in European, African, Middle Eastern and South Asian populations over the last 10,000 years,” Thomas continued.
The lactase persistence trait was favored by evolution and is extremely common in some populations today. In Northern Europe, more than 90% of people are lactase persistent. The same is true of some populations in Africa and the Middle East. But there are also many populations where lactase persistence is much rarer: many Africans don’t have the trait, and it’s rare in Asia and South America.
Based on the study results, the research team proposed that those in prehistoric Eurasia who ate dairy products while lactose intolerant encouraged natural selection of the lactase persistence gene in humans over the time period analyzed. However, they admit that population fluctuations, settlement density and the exploitation of wild animals “offer better explanations” for the selection of lactase persistence than the use of milk during that time.
Negative symptoms associated with milk consumption only occur in some people who are lactose intolerant, probably due to variations in colon bacteria.
Referencia: Evershed, R.P., Davey Smith, G., Roffet-Salque, M. et al. Dairying, diseases and the evolution of lactase persistence in Europe. Nature (2022). https://doi.org/10.1038/s41586-022-05010-7