The Adopted Field

The default model for the spread of agriculture is population replacement. Farmers arrive. Hunter-gatherers are displaced. The crops and the people who grew them moved together — a package deal. This model draws from the European Neolithic transition, where ancient DNA showed significant genetic turnover as farming spread from the Near East.

Ancient DNA from 46 individuals spanning 2,200 years in Argentina's Uspallata Valley tells a different story. The local hunter-gatherers adopted farming without being replaced. Genetic continuity is strong between the earliest hunter-gatherers in the sequence and the people living more than a thousand years later who grew maize and other crops. The crops arrived. The people stayed the same.

This is adoption without migration — or more precisely, adoption where the migrants were absorbed rather than dominant. The farming technology spread through the local population by cultural transmission, not demographic replacement. The people who farmed in the Uspallata Valley a thousand years ago were the descendants of the people who hunted and gathered there two thousand years ago.

The complication arrives around 800-600 years ago. A group of migrants appeared at the Potrero Las Colonias burial site — people heavily dependent on maize, showing isotopic signatures among the highest recorded in the southern Andes. These migrants were genetically related to local groups and came from nearby regions, not distant populations. But they were in trouble: the genetic data reveals a sharp and long-term population decline, with evidence of malnutrition, disease, and tuberculosis. They survived through family networks and kinship bonds rather than conquest.

The pattern is the inverse of the European model. In Europe, farmers replaced hunter-gatherers. In the Uspallata Valley, hunter-gatherers adopted farming and then received collapsing farming communities. The local population was the stable element; the migrants were the fragile ones.

The through-claim: the European Neolithic model is not a universal mechanism. It is a regional outcome — one way that agriculture can spread, in one place, under one set of conditions. In Argentina, the same transition produced the opposite population dynamic. The crops were the same kind of innovation. The human response was not.