Multi-isotopic and morphometric evidence for the migration of farmers leading up to the Inka conquest of the southern Andes

Abstract

We present isotopic and morphometric evidence suggesting the migration of farmers in the southern Andes in the period AD 1270-1420, leading up to the Inka conquest occurring ~ AD 1400. This is based on the interdisciplinary study of human remains from archaeological cemeteries in the Andean Uspallata Valley (Argentina), located in the southern frontier of the Inka Empire. The studied samples span AD 800-1500, encompassing the highly dynamic Late Intermediate Period and culminating with the imperial expansion. Our research combines a macro-regional study of human paleomobility and migration based on a new strontium isoscape across the Andes that allows identifying locals and migrants, a geometric morphometric analysis of cranio-facial morphology suggesting separate ancestral lineages, and a paleodietary reconstruction based on stable isotopes showing that the migrants had diets exceptionally high in C₄ plants and largely based on maize agriculture. Significantly, this migration influx occurred during a period of regional demographic increase and would have been part of a widespread period of change in settlement patterns and population movements that preceded the Inka expansion. These processes increased local social diversity and may have been subsequently utilized by the Inka to channel interaction with the local societies.

Figure 1

(a) Map of the southern Andes showing the study area (within the rectangle) and the locations of rodent sampling sites for bioavailable strontium (black dots); (b) Archaeological sites with human remains in the Uspallata Valley; (c) Panoramic view of the Uspallata Valley with the Andean Frontal Cordillera behind. Maps generated with Quantum GIS, version 3.2.3 (https://www.qgis.org) and edited with Inkscape 0.92 (https://inkscape.org).

Figure 2

Framework for the study of bioavailable strontium in the southern Andes: (a) Main geological provinces: (1) Pacific Coast, (2) Coastal Cordillera, (3) Eastern Principal Cordillera, (4) Western Principal Cordillera, (5) Frontal Cordillera; (6) Precordillera, (7) Quaternary Active Foreland; (b) Isoscape of strontium isotopes (⁸⁷Sr/⁸⁶Sr) in rodent samples for the southern Andes of central Argentina and Chile. Map generated with Quantum GIS, version 3.2.3 (https://www.qgis.org) and edited with Inkscape 0.92 (https://inkscape.org). (a) Using public domain data from SEGEMAR (https://sigam.segemar.gov.ar/visor/) and modified from (Copyright Clearance Center License ID 1055264-1).

Figure 3

(a) Strontium values from human and rodent samples from the Uspallata Valley and nearby areas; (b) Bayesian modelling, KDE, and inverted histogram of individuals with local (green) and non-local (red) values compared to the estimated date (blue) for the Inka arrival; (c) Summed probabilities (thin black line) and KDE (blue curve) for radiocarbon dates from Mendoza compared to the KDE for migrants. Figures generated with Excel 16.39 (ID: 02954-035-637535) and OxCal 4.3 (https://c14.arch.ox.ac.uk/oxcal.html) and edited with Inkscape 0.92 (https://inkscape.org).

Figure 4

(a) Cranio-facial geometric variation and paleodiet in human remains from Uspallata: PCA of cranio-facial variation; (b) PCA of the cranial base variation; (c) PCA of the cranial vault variation; (d) δ¹³C_collagen and δ¹³C_apatite in sites from Uspallata compared to theoretical endmembers for C₃ hunter-gatherer and C₄ farmer diets^,, total area of the group—dotted line—and Standard Ellipse Area corrected for small sample size (SEA_C)—continuous line; and (e) Standard Ellipse Area Bayesian (SEA_B). Figures generated with R version 3.6.2 (https://www.R-project.org) and Excel 16.39 (ID: 02954-035-637535) and edited with Inkscape 0.92 (https://inkscape.org).