Migration and biological continuity in central Mexico during the Classic-Epiclassic transition

Objectives: The role of migration in the cultural development of central Mexico has long been debated. Archaeological models suggest that central Mexico likely experienced increased migration during the Epiclassic period (600-900 CE) and that migrants may have originated in northwestern Mexico. While previous biodistance analyses of Classic and Postclassic populations have come to similar conclusions, none have incorporated Epiclassic skeletal populations. This study uses multi-scalar biodistance analyses to directly evaluate archaeological Epiclassic migration models within central Mexico.Materials and Methods: This study uses finite mixture and relationship (R) matrix analyses of cervicometric tooth dimensions to reconstruct patterns of biological affinity among Classic and Epiclassic Mesoamerican populations (n = 333), including at the central Mexican Epiclassic shrine site of Non-Grid 4 where the remains of at least 180 individuals were interred.Results: Estimated inter-site phenotypic distances demonstrate support for some degree of both biological continuity and extra-local gene flow within central Mexican populations during the Classic-Epiclassic transition. Furthermore, estimated phenotypic distances and finite mixture posterior probabilities indicate central Mexican Epiclassic populations were biologically diverse, originating from various source populations throughout Mesoamerica, including the Bajio region, the Malpaso Valley, and the Oaxaca Valley.Discussion: Results suggest that emphasizing both local and extra-local gene flow rather than population replacement may be more appropriate to understand central Mexican population structure during the Classic-Epiclassic transition. Moreover, analyses support previous archaeological migration models positing that Epiclassic migrants into central Mexico originated in northwestern Mexico, but also find evidence of Epiclassic migrants originating from previously unanticipated locales like southern Mexico.