An area called the central Southern Cone in South America, which consists of a large part of Argentina, is known to be one of the last global regions to become inhabited by humans.

Despite research indicating migration into the area over 12,000 years ago, there is currently little DNA research that describes the lineages associated with the area. To remedy this problem, a group of DNA researchers conducted a genome-wide study on ancient individuals from the region. The new research is published in Nature.

Analyzing 10,000 years of DNA

"The peopling of South America likely followed both the Pacific and Atlantic coasts. Genetic differentiation is detectable in ancient genomic data after 9,000 bp in at least three main clusters: central Andes, tropical/subtropical forest or lowlands (including Amazonia), and central Chile, Patagonia and Pampas. However, current sampling has major gaps. We focus on the poorly sampled central Southern Cone (CSC)—the territory of central and northern Argentina comprising the Andean mountains in the west to the eastern fluvial plains and southern grassland plains," the study authors write.

The team screened 344 bone and tooth samples from 310 individuals who lived between 10,000–150 years ago, and were able to obtain genome-wide data from 238 of them. They enriched ancient DNA libraries for more than 1.2 million targeted single-nucleotide polymorphisms (SNPs), and compared the newly reported individuals with previously reported data for 588 pre-European contact (over 600 years ago) Native or Indigenous Americans.

They also included data from present-day Native Americans. They then used statistical analyses to determine population structure, mixing between groups, and community sizes.

A missing link is found

The team's main finding was a previously unknown deep genetic lineage that had existed in central Argentina for at least the last 8,500 years. They say this lineage has persisted over this time, and that modern Argentinians still share DNA with this group. The group had apparently persevered through millennia, despite periods of severe drought in the region.

The study authors write, "We found that the central Argentina lineage is geographically structured along two clines, one reflecting admixture with central-Andes-like ancestry and the other with Middle Holocene Pampas-like ancestry."

This lineage coexisted with others and became the main ancestry in the Pampas after 800 years ago. The deep central Argentina lineage had expanded southward, admixing with other groups at least 3,300 years ago, according to their analysis. The team also points to genetic connectivity between the people of central Argentina and central Andes lineages as early as 4,600 years ago.

The work provides a genetic framework for understanding Indigenous population history in Argentina and the Southern Cone, helping to fill in the missing pieces of Argentina's history.

Millennia of continuity

Although the group appeared to have intermingled with others to an extent, the researchers note evidence that they largely kept to themselves. Evidence exists for multiple languages in the region, but also for genetic homogeneity. The team says this may be partially due to a kinship-based organizational structure that persisted in some Argentinian populations. The analysis showed evidence of increased close-kin unions in northwest Argentina, which paralleled those in the central Andes.

"This was interpreted as the origin or widespread adoption of the ayllu system—a social and political unit bound together by rules of kinship affiliation and reciprocity, with preference of within-group marriage to facilitate cooperation and keep resources within the community," the study authors explain.

Whatever the reason, the evidence shows limited gene flow among communities for long periods. Future studies with more densely sampled time series, especially from underrepresented regions and periods, could further clarify the lack of migration and admixture between groups.

Edited by Stephanie Baum, reviewed by Robert Egan