Ancient DNA from forty-six individuals spanning two thousand years in Argentina's Uspallata Valley tells a simple story with complicated implications. The people who became farmers were the same people who had been hunter-gatherers. No influx of farming populations. No replacement. No significant admixture with outsiders. The genes stayed. The subsistence strategy changed.
This contradicts the demic diffusion model — the dominant explanation for how agriculture spread globally — which holds that farming peoples expanded into new territories, carrying their genes and their crops together. In Europe, the Neolithic spread largely did work this way: Anatolian farmers migrated west, mixing with and often replacing local hunter-gatherers. The model was generalized into a principle.
In the southern Andes, the principle breaks. Barberena, Luisi, Rascovan, and colleagues show strong genetic continuity across the transition. The local population learned agriculture — probably from neighboring groups already practicing it — without being absorbed or displaced. Ideas moved. People didn't.
The second finding complicates the narrative further. Later maize-dependent communities in the same valley experienced stress, malnutrition, disease — including pre-contact tuberculosis — and demographic decline. Agriculture was not a civilizational upgrade. It was a trade-off that, in this specific environment, eventually produced a health crisis.
The local population chose farming. Then farming chose them — locking them into a subsistence pattern that degraded their health and reduced their numbers. The adoption was voluntary. The consequences were not. Three members of the Huarpe Indigenous community co-authored the study, adding contemporary perspective to the deep-time genetic data.