Bronze Age skull in situ in the Tollense Valley. Photo credit: Stefan Sauer / Tollense Valley Project
- A new study published in Current biology shows that the human ability to digest milk (lactase persistence) is spreading evolutionarily rapidly in Central Europe.
- The study tested 1,200 B.C. Genetic material from the bones of warriors in Germany, and researchers found that lactase persistence spread in just a few thousand years.
- The results suggest that the ability to digest milk may have given a great evolutionary advantage to these ancient European peoples who passed the lactase-persistent gene on to future generations.
Humans’ ability to digest milk as adults has changed our eating habits and societies for centuries. But when and how this ability – known as lactase persistence or lactose tolerance – appeared and established itself is up for debate. An international team of scientists, including Krishna Veeramah, PhD, of Stony Brook University, tested the genetic material from the bones of people killed during a battle in the Bronze Age around 1200 BC. Years died, an extremely rapid transformation compared to most evolutionary changes in humans. Your results will be published today (September 3, 2020) in Current biology.
Various bones from a Bronze Age excavation site, some of which have been genetically tested to determine the presence of the lactase-persistent gene. Photo credit: Stefan Sauer / Tollense Valley Project
Despite the importance of milk drinking in Europe and North America, around two thirds of the world’s population are lactose intolerant today. Generally, no mammal digests milk as an adult, so humans should not give milk to adult cats or dogs, for example. However, a subgroup of humans has a genetic mutation that enables the enzyme lactase to digest the lactose sugar contained in milk throughout a person’s life. Many of these people come from Central or Northern Europe.
The battle took place on the banks of the Tollense, a river in what is now Germany, and is the most significant that we know from the Bronze Age in Europe. It is likely made up of around 4,000 warriors, almost a quarter of whom died during the fighting. Although the researchers were more than three thousand years old, they were able to sequence DNA of some of the bone fragments recovered from the battlefield.
Veeramah, associate professor in the Department of Ecology and Evolution at the College of Arts and Sciences, led part of the research that analyzed how the overall genetic lineage of battlefield populations compared to other modern and ancient populations, and then the frequency of that Lactase-persisting allele for other modern and ancient populations, particularly medieval European populations.
Archaeologists have been systematically searching for a section along the Tollense for more than 10 years. Photo credit: Stefan Sauer / Tollense Valley Project
The research team led by Joachim Burger and colleagues from Johannes Gutenberg University Mainz (JGU) found that despite the struggle more than 4,000 years after the introduction of agriculture in Europe – which in part entailed the consumption of dairy products from early cattle domesticated goats and sheep – only one in eight warriors had a genetic variant that enabled them to break down lactose.
“If we look at other European genetic data from the early Middle Ages less than 2,000 years later, we find that more than 60 percent of people could drink milk as adults, similar to what we see in modern Central European countries ranging from 70 to 90 Percent, ”said Veeramah. “This is an incredibly fast rate of change in the gene that controls milk digestion. It appears that previous European individuals with the ability to digest lactose had a six percent higher chance of fathering children by possessing this one genetic mutation than those who couldn’t. This is the strongest evidence of positive natural selection in humans. ”
Joachim Burger of JGU, lead author of the study, added that there is still no definitive answer to the question: Why did the ability to digest the sugar in milk after infancy offer such a great evolutionary advantage?
“Because milk is a high-energy, relatively uncontaminated drink, it may have a better chance of survival in the event of food shortages or if the drinking water supply has been contaminated,” said Burger.
Reference: “Low prevalence of lactase persistence in the Bronze Age in Europe indicates a sustained strong selection in the last 3,000 years” by Joachim Burger, Vivian Link, Jens Blöcher, Anna Schulz, Christian Sell, Zoé Pochon, Yoan Diekmann, Aleksandra Žegarac, Zuzana Hofmanová, Laura Winkelbach, Carlos S. Reyna-Blanco, Vanessa Bieker, Jörg Orschiedt, Ute Brinker, Amelie Scheu, Christoph Leuenberger, Thomas S. Bertino, Ruth Bollongino, Gundula Lidke, Sofija Stefanović, Detlef Jantzen, Elke Kaiser, Thomas Terberger , Mark G. Thomas, Krishna R. Veeramah and Daniel Wegmann, September 3, 2020, Current biology.
DOI: 10.1016 / j.cub.2020.08.033
