Was there a population replacement during the Late mid-Holocene in the southeastern Pampas of Argentina? Archaeological evidence and Paleoecological basis

Based on radiocarbon and craniofacial morphological evidence, we propose that a population replacement took place in the southeastern Pampas of Argentina sometime between 6000 and 3500 years BP. The analysis of the available radiocarbon database shows that there is a significant gap between 5960 and 5060 14C years BP. The morphometric analyses of samples of human crania corresponding to the early mid-Holocene (ca. 8000-6000 14C years BP) and to the early late-Holocene (ca. 3500-2000 14C years BP) strongly suggest that they probably belonged to at least two different biological populations. We contend that this population event must be considered the outcome of a local population contraction/extinction process, followed by the later expansion/dispersal of a new population into the area. This is consistent with the expectations of metapopulation ecology and evolutionary geography, which predict that increasing extinction risks select for higher dispersal rates, since local population contraction or extinction often result in empty or thinly populated patches, whose existence makes dispersal both feasible and profitable. A slightly corrected version of the model advanced by Politis (1984), that establishes a linkage between the climatic induced demographic and range contraction of critical mammalian resources (e.g., guanaco) and those of human populations, is still useful to explain situations such as the alleged mid-Holocene population replacement event.