A new study of ancient DNA from 46 individuals buried across thousands of years in Argentina’s Uspallata Valley has found that farming arrived in the southern Andes not through waves of migrating outsiders but through local hunter-gatherers who adopted agriculture on their own terms. The research, led by the Microbial Paleogenomics Unit at Institut Pasteur and published in Nature, challenges a long-standing assumption that the spread of crops like maize required the movement of farming populations into new territory. Instead, the genetic record points to deep continuity among the people of Mendoza Province, even as their way of life changed dramatically.
Genetic Continuity Across Millennia
The central finding rests on genome-wide data from 46 individuals spanning the period from pre-farming hunter-gatherers to later maize-cultivating communities in the Uspallata Valley. Rather than detecting a genetic rupture, the kind that would signal replacement of one population by another, the researchers found strong continuity in ancestry across the transition to agriculture. The people who began growing crops around 2,000 years ago were, genetically speaking, the same population that had hunted and foraged in the valley for thousands of years before.
This distinction matters because the debate over how farming spread globally has long been split between two models. One, called demic diffusion, holds that farmers physically moved into new regions and either absorbed or displaced existing populations. The other argues that knowledge and crops traveled through exchange networks while local populations stayed put. In much of Europe, ancient DNA has supported the demic diffusion model, showing clear genetic turnover when farming arrived from the Near East. The Uspallata evidence suggests the southern Andes followed a fundamentally different path, with cultural and economic change outpacing any large-scale movement of people.
A broader archaeogenetic study of 238 ancient individuals across Argentina and adjacent regions reinforces this picture. That dataset revealed long-term genetic structure and continuity in central Argentina, with a distinct regional ancestry component persisting over millennia. The Uspallata Valley fits within that pattern: a population that remained genetically stable even as it absorbed new technologies and food systems from the north. A complementary look at supplementary materials for the Uspallata study further details subtle shifts in ancestry proportions without any wholesale replacement, underscoring the depth of local continuity.
What the Crops Themselves Reveal
The human genetic record is only half the story. Parallel work on the crops these communities grew offers a second line of evidence. Research on ancient common beans (Phaseolus vulgaris), including archaeological samples from Argentina, has shown that early Andean farmers actively selected for desirable traits in beans while still preserving significant genetic diversity in the crop. That balance between selection and diversity is a hallmark of careful, locally managed agriculture rather than the rapid, intensive monoculture associated with large-scale population movements.
The bean genomics work provides a concrete mechanism for understanding how farming could spread without farmers. If crop varieties moved through trade or social networks, local communities would have adapted those plants to their own soils, climates, and preferences over generations. The preserved diversity in Phaseolus genomes from the region is consistent with exactly that kind of gradual, community-level adaptation. It also suggests these early cultivators were skilled enough to manage genetic resources in ways that maintained the crop’s long-term viability and resilience to environmental stress.
Evidence from the Uspallata Valley itself supports this slow, negotiated adoption of agriculture. As summarized in coverage of the new research, maize and other crops expanded into the valley in stages, initially supplementing rather than replacing wild resources. Over time, farming became more central to subsistence, but the underlying community remained the same people whose ancestors had long exploited the valley’s diverse ecological niches.
Radiocarbon Dating Fills the Timeline
Pinning down exactly when people and crops moved through the southern Andes requires more than genetics. A radiocarbon-focused analysis of the Uspallata region in Mendoza Province has provided site-level chronologies that help reconstruct the timing and mode of human migrations in the area. These dates serve as a non-genetic backbone for the broader narrative, confirming that the valley was continuously occupied and that any population movements were incremental rather than sudden.
The radiocarbon evidence also helps rule out alternative explanations. If farming had arrived with a large migrant group, the archaeological record would likely show an abrupt shift in settlement patterns, tool types, and burial practices at a single point in time. Instead, the chronological data from the Uspallata region show a gradual transition, with new agricultural practices layered onto existing ways of life over centuries. Small-scale contacts, seasonal mobility, and exchange networks appear to have been sufficient to introduce new crops and techniques without fundamentally reshaping the valley’s demographic base.
Crises Hidden in the Bones
Adopting farming was not a smooth upgrade. The Institut Pasteur-led study also found evidence that the shift to agriculture brought serious problems. Denser, more settled populations created conditions for infectious disease outbreaks, including tuberculosis, that coincided with population declines. At the same time, environmental stress and the arrival of migrants from the north added pressure to communities already dealing with the consequences of their new way of life.
This pattern, in which agriculture brings both resilience and new vulnerabilities, is well documented in other parts of the world. But the Uspallata case adds a distinctive element. Because the population remained genetically continuous, the crises that followed farming cannot be blamed on conflict between newcomers and locals. Instead, the evidence points to disease and environmental strain as the primary threats, problems that emerged from the agricultural transition itself rather than from outside invasion. According to reporting on the study, farming helped communities manage certain crises by stabilizing food supplies but also created dense, interconnected settlements that sustained infectious disease.
Why Local Adoption Changes the Narrative
Most coverage of ancient DNA studies tends to emphasize dramatic population replacements, the kind of stories where one group sweeps in and transforms a region. The Uspallata Valley offers a quieter but equally consequential narrative. Here, local hunter-gatherers gradually reshaped their economy, social organization, and health landscape without losing their genetic identity. Farming was not something done to them by outsiders; it was something they learned, adapted, and ultimately made their own.
This has implications well beyond a single Andean valley. The combination of ancient genomes, regional datasets from wider Argentina, crop genetics from common beans, and radiocarbon chronologies demonstrates how different strands of evidence can converge on a model of continuity rather than replacement. It suggests that in some regions, the spread of agriculture may have been less about the movement of people and more about the circulation of ideas, plants, and practices through existing social networks.
By foregrounding local agency, the Uspallata findings also complicate simplistic narratives of progress. Farming brought new resources and strategies for coping with climate variability, but it also exposed communities to novel diseases and environmental pressures. The same continuity that makes this case so striking (the fact that the descendants of ancient hunter-gatherers became farmers in place) also meant that the costs of transition were borne by the same lineages over many generations.
In the end, the Uspallata Valley shows that big transformations in human history do not always come with clear breaks in who people are. Sometimes, as in this corner of the southern Andes, the most profound changes happen when communities stay put and slowly reinvent how they live on the land they have long called home.
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*This article was researched with the help of AI, with human editors creating the final content.
