Pampas Echoes: Arroyo Seco II (7200 BP)

Arroyo Seco II sits in the grassed lowlands of the Argentine Pampas, an open-air locus of human activity during the early Holocene. Radiocarbon dates from stratified deposits place occupation in the window between roughly 5462 BCE and 5000 BCE (about 7200 years before present). Archaeological data indicates repeated short-term camps: lithic scatters, hearth features, and human remains that together sketch a picture of mobile hunter-gatherer groups exploiting riverine and grassland resources.

The environment after the Last Glacial Maximum was changing — warming climates and shifting faunal assemblages opened new ecological niches across the Southern Cone. Limited evidence suggests Arroyo Seco II was part of a broader network of seasonal loci rather than a single sedentary settlement. Material culture is characterized by locally made stone tools; however, regional connections are plausible through raw-material sourcing and tool styles. Genetic data from two individuals recovered at the site provide an additional lens on origin narratives: both carry the maternal lineage C1c, a branch known from early South American contexts, while paternal assignments include Q and P. These genetic signals align with models of early peopling that emphasize multiple dispersal corridors into South America and subsequent localized diversification. Because the sample size is extremely small, interpretations about population origins remain tentative and highlight the need for more integrated archaeological and genomic sampling across the Pampas and adjacent regions.

Ancient DNA from two individuals at Arroyo Seco II provides a rare genetic snapshot of early Holocene inhabitants of the Southern Cone. Both individuals share mitochondrial haplogroup C1c, a maternal lineage observed in other early and later populations of South America and consistent with a deep-rooted maternal ancestry in the region. The recurrence of C1c in both samples suggests local maternal continuity, but with only two genomes this inference is preliminary.

Y-chromosome assignments include haplogroup Q in one individual and P in the other. Haplogroup Q is a well-documented paternal lineage among Native American populations and aligns with expectations for early South American males. The call of P for the second individual could reflect a less-resolved or upstream assignment in low-coverage data—haplogroup P is the wider clade that ancestrally contains Q and R—or it might indicate a rare or divergent paternal lineage. Archaeological context combined with these genetic markers supports models in which early colonizing groups carried a subset of founding maternal lineages while paternal diversity fluctuated regionally.

Caveats: the sample count is very low (n=2), so population-level conclusions are tentative. Additional well-preserved genomes from Arroyo Seco II and surrounding sites are necessary to clarify the extent of maternal continuity, the frequency of paternal lineages, and the relationship of these people to later Indigenous groups across Patagonia and the Pampas.