Ancient DNA reveals farming spread through migration, locals slow to adopt it

(Press-News.org) UNIVERSITY PARK, Pa. — Roughly 10,000 years ago, humans started shifting from being nomadic hunter-gatherers to building large agricultural settlements, marking one of the greatest transformations in human history. This transition, known as the Neolithic Revolution, began in the Fertile Crescent of the Middle East and led to the spread of farming throughout Europe. For decades, researchers have debated what drove this change. Did farming spread mainly because farmers themselves moved into new lands, or because hunter-gatherers adopted farming practices?

New interdisciplinary research by scientists at Penn State provides the clearest answer to date. Using mathematical models, computer simulations, and ancient DNA analysis, the team was able to measure how migration and cultural adoption each contributed to the expansion of farming. Their findings, published this week (Aug. 25) in Nature Communications, show that migration of farming groups was the dominant factor, while cultural adoption by hunter-gatherers only played a minimal role.

“Archaeology and genetics offer complementary windows onto this transition,” explained Christian Huber, assistant professor of biology at Penn State and senior author on the paper. “For example, artifacts and isotopes in ancient bones can reveal whether a person relied on domesticated plants or animals, reflecting the adoption of new farming practices. At the same time, DNA preserved in those bones can show where people’s ancestors came from, providing evidence of migration, or the movement of farming populations into new regions.”

Using sophisticated computer simulations, ancient DNA and archaeological evidence, Huber’s team was able to measure the forces that drove farming’s expansion — and how influential each force was.

“This has been a long-standing question — and disentangling the roles of migration and cultural adoption has been a goal of archaeologists and anthropologists for decades,” said Troy LaPolice, doctoral student at Penn State and lead author of the study. “What we found was surprising: when cultures spread through migration, it is not guaranteed local ancestry patterns will change, but the spread of farming managed to leave a strong and lasting impact on European ancestry.”

By building models that simulate population movement, growth and cultural learning, and fitting them to the known rate of farming expansion and ancestry data from 618 European Neolithic individuals derived from ancient DNA, the team was able to quantify the contributions of both migration and cultural adoption.

“It's really interesting to be able to understand a time period before any written or oral history,” LaPolice said. “This intense interdisciplinary project allowed us to undertake a new kind of historical reconstruction.”

The team found that the adoption of new ideas and practices did not significantly accelerate the spread of agriculture. Hunter-gatherers appear to have largely continued to forage even as farming expanded and gradually displaced their way of life. The contribution of cultural transmission to farming’s spread, known as the “cultural effect,” was minimal, estimated at only about 0.5%.

“The assimilation rate, the rate at which hunter-gatherers were grafted into farming communities, was actually very low — only about one in 1,000 farmers converted a hunter-gatherer to farming each year,” Huber said. “As a result, cultural transmission had almost no effect on how quickly farming spread. Still, even at this low rate, it left a lasting mark on the DNA of Europeans today and introduced useful genetic traits into the growing farming communities.”

The researchers also found that mating was largely restricted to within cultural groups, meaning farmers predominantly mated with other farmers and hunter-gatherers with other hunter-gatherers. Any “between-group mating” was remarkably rare, estimated at less than 3%, according to their models. This aligns with evidence from other ancient DNA studies showing minimal gene flow even where foragers and farmers co-existed for centuries, explained Matthew Williams, academic affiliate assistant professor of biology and co-author on the paper.

Williams and Huber have also published two recent papers where they tested commonly used methods for studying ancestry in ancient people. Their work shows how these tools can shed light on human movement through history, but also points out where they can be misleading if used without care. One paper was published in Genome Biology and the other in Genetics.

“This research highlights the power of combining genetic data with archaeological models to uncover the complex behavioral mechanisms of our past,” Williams said. “Looking forward, I see this paving the way for a re-evaluation of other major prehistoric cultural shifts.”

The U.S. National Institutes of Health funded the research.

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