Arroyo Seco II — 7400 BP Window

Arroyo Seco II sits like a quiet ledger of human movement in the rolling Pampas: hearth‑stained sediments, stone tools, and burials that speak of lifeways shaped by open grasslands and riverine resources. Radiocarbon dates from material associated with human remains place the activity at roughly 5620–5336 BCE, a moment in the Early Holocene when climates were stabilizing after the last glacial fluctuations. Archaeological data indicate seasonal mobility, intimate knowledge of river corridors, and a lithic technology adapted to hunting and processing.

Genetically, this horizon fits into the wider picture of early South American populations who carried lineages ultimately derived from the initial peopling of the Americas. However, the genetic sample from Arroyo Seco II is a single individual; limited evidence suggests continuity of maternal lineages such as mtDNA A2 across much of the continent, but local demographic histories can be complex. The cinematic sweep of the Pampas — winds, tall grasses, a small hearth smoked at dusk — is thus anchored by careful science: stratigraphy, radiocarbon measurement, and DNA sequencing that together trace origins without overstating certainty.

The genetic data from Arroyo Seco II are sparse but illuminating. One sequenced individual carries mitochondrial haplogroup A2, a lineage widely observed among ancient and modern Indigenous populations throughout the Americas. This maternal signal is consistent with the genetic legacy of the first peoples who spread through South America in the Late Pleistocene and Early Holocene.

Because only one genome is available, any population‑level inference must be made cautiously. The absence of reported Y‑DNA haplogroups prevents direct inference about paternal lineages. Nonetheless, the presence of mtDNA A2 aligns with archaeological expectations of deep continuity in maternal ancestry across broad regions. Comparative ancient DNA from other South American sites shows varied local patterns of ancestry and admixture through time, so the Arroyo Seco II result contributes a valuable but preliminary datapoint. Ongoing sampling and higher sample counts will be necessary to resolve local demographic events, gene flow, and potential links with neighboring groups.