Abstract
BackgroundArchaeology reports millenary cultural contacts between Peruvian Coast-Andes and the Amazon Yunga, a rainforest transitional region between Andes and Lower Amazonia. To clarify the relationships between cultural and biological evolution of these populations, in particular between Amazon Yungas and Andeans, we used DNA-sequence data, a model-based Bayesian approach and several statistical validations to infer a set of demographic parameters.ResultsWe found that the genetic diversity of the Shimaa (an Amazon Yunga population) is a subset of that of Quechuas from Central-Andes. Using the Isolation-with-Migration population genetics model, we inferred that the Shimaa ancestors were a small subgroup that split less than 5300 years ago (after the development of complex societies) from an ancestral Andean population. After the split, the most plausible scenario compatible with our results is that the ancestors of Shimaas moved toward the Peruvian Amazon Yunga and incorporated the culture and language of some of their neighbors, but not a substantial amount of their genes. We validated our results using Approximate Bayesian Computations, posterior predictive tests and the analysis of pseudo-observed datasets.ConclusionsWe presented a case study in which model-based Bayesian approaches, combined with necessary statistical validations, shed light into the prehistoric demographic relationship between Andeans and a population from the Amazon Yunga. Our results offer a testable model for the peopling of this large transitional environmental region between the Andes and the Lower Amazonia. However, studies on larger samples and involving more populations of these regions are necessary to confirm if the predominant Andean biological origin of the Shimaas is the rule, and not the exception.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-014-0174-3) contains supplementary material, which is available to authorized users.
Highlights
Archaeology reports millenary cultural contacts between Peruvian Coast-Andes and the Amazon Yunga, a rainforest transitional region between Andes and Lower Amazonia
We used genetic data and a population genetic model to infer the evolutionary relationships between a Quechua population from the Peruvian Central Andean Highlands and an Arawak Matsiguenga population (Shimaa) from the Southern Peruvian Amazon Yunga (Additional file 1: Figure S1)
We inferred the parameters of the model using the likelihood-based method implemented in the software IM. This method uses the entire information provided by the data and applies a Markov Chain Monte Carlo (MCMC) computational approach [24]. Even though this model reduces the complex history of two populations, that evolve together with surrounding groups, to an only-two-populations system, simulation studies have shown that inferences are robust, despite moderate violations of the model assumptions, which were simulated to mimic comparable situations often encountered in real-world scenarios [25]
Summary
Archaeology reports millenary cultural contacts between Peruvian Coast-Andes and the Amazon Yunga, a rainforest transitional region between Andes and Lower Amazonia. The Inca Empire is just the tip of the iceberg of a long-term cultural and biological evolutionary process that involved the entire Andean region and its adjacent Pacific Coast (hereafter western South America). This process began 14–11 thousand years BP, with the peopling of this region in the Late Pleistocene [2], involving continuous cultural exchanges and gene flow along time, and leading to a relative genetic, cultural, and linguistic homogeneity between the populations of western. Each of the Horizons corresponds to periods of material cultural dispersion involving a wide geographic area and, in the case of Middle and Late Horizons, to the expansion of the Wari-Tiwanaku and Inca States, respectively [8]
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