Science News

from research organizations

Ancient DNA reveals a farming shift that pushed a society to the brink

Date:

March 21, 2026

Source:

Institut Pasteur

Summary:

A new study reveals that farming in Argentina’s Uspallata Valley was adopted by local hunter-gatherers rather than introduced by outside populations. Centuries later, a stressed group of maize-heavy farmers migrated into the region, facing climate instability, disease, and declining numbers. Despite these pressures, there’s no sign of violence—instead, families stayed connected across generations, using kinship networks to survive. The research shows how cooperation, not conflict, helped communities navigate crisis.

Facebook

Twitter

FULL STORY

Illustration representing population movements within the Southern Andes as a resilience strategy to face crises. Credit: Mauricio Álvarez - studio FIEL®

A new interdisciplinary study published in Nature traces more than 2,000 years of population history in Argentina's Uspallata Valley (UV), a key southern edge of ancient Andean farming. The research offers new insight into how agriculture reshaped societies and how people coped with long periods of hardship. By combining ancient human and pathogen DNA with isotopic data, archaeology, and paleoclimate records-and working closely with Huarpe Indigenous communities-the team shows how local hunter-gatherers adopted farming, how later maize-based societies faced sustained stress, and how strong family connections may have helped people endure instability.

One long-standing question is whether agriculture spread mainly through migrating farmers or through local groups adopting crops and techniques. Archaeological evidence alone often cannot clearly separate these possibilities, since both can produce similar material remains. The Uspallata Valley provides a rare opportunity to explore this question because farming arrived there later than in other parts of South America.

Researchers led by the Microbial Paleogenomics Unit (MPU) at Institut Pasteur analyzed genome-wide ancient DNA from 46 individuals, spanning early hunter-gatherers to later farming populations. The results show strong genetic continuity between hunter-gatherers (~2,200 years ago) and people living more than 1,000 years later as maize farming-and other crops-spread. This suggests that farming was largely adopted by local populations rather than introduced by large incoming groups.

Deep Genetic Roots and Indigenous Continuity

The findings also fill an important gap in understanding the genetic history of southern Andean populations. "Beyond the local story of Uspallata, we are also filling a gap in South American human genetic diversity by documenting a genetic component that was previously only suggested by analysing present-day populations, and that now proves to have a very deep divergence and current persistence in the region," explains Pierre Luisi, co-first author of the study, researcher in CONICET, Argentina, who started this work as postdoc in the MPU at Institut Pasteur, France.

"The persistence of this ancestral genetic component in populations today has important implications, since it argues against narratives claiming the extinction of indigenous descendants in the region since the establishment and growth of the Argentine state-nation."

Diet, Mobility, and a Shift to Intensive Maize Farming

To understand daily life, researchers analyzed stable isotopes preserved in bones and teeth. Carbon and nitrogen isotopes reveal long-term diet, while strontium isotopes indicate where a person lived and whether they moved during their lifetime.

The data show that maize consumption changed over time, pointing to flexible farming practices rather than a steady shift toward full agricultural dependence. However, between ~800 and 600 years ago, a different pattern emerged at a major burial site called Potrero Las Colonias. Many individuals there relied heavily on maize-among the highest levels recorded in the southern Andes-and showed non-local strontium signatures, indicating they had moved into the area. Who were these migrants, and where did they come from?

Migration, Decline, and Signs of Stress

Further genetic and isotopic evidence suggests these migrants came from nearby regions rather than distant populations. They were closely related to local groups and part of the same broader population network. Even so, genomic data reveal that this group experienced a sharp and long-term population decline, indicating ongoing stress across generations.

Multiple lines of evidence point to a complex crisis. Paleoclimate records show extended periods of environmental instability that coincide with the population decline. At the individual level (individual's lives), skeletal remains show signs of childhood malnutrition and disease. Ancient DNA also revealed tuberculosis at the site, belonging to a lineage known from pre-contact South America. I