Geographic substructure in craniometric estimates of admixture for contemporary American populations

Abstract

There is considerable variation in admixture estimates, not just between, but notably within, all four of the populations. This substructure can be explained by differences in geography, including regions, divisions, and states. This article's findings agree with census trends and speak broadly to admixture dynamics and ancestral diversity among contemporary Americans. They are also specifically relevant to those cases in the FDB. The presence of subpopulations has implications for cranial research, forensic identification, and studies of biological variation in the United States.

Understanding (Mis)classification Trends of Latin Americans in Fordisc 3.1: Incorporating Cranial Morphology, Microgeographic Origin, and Admixture Proportions for Interpretation

“…Those identified cases with known Mexican state of origin were assigned to one of three geographic regions: North ( n = 35), Central ( n = 42), or South ( n = 60) Mexico. This regional schema for Mexican states replicates the partitions used in previous studies to facilitate easy comparison of results . The majority of individuals included in the PCOME sample were either confirmed (via DNA) or estimated (using traditional forensic anthropological methods) to be male, while approximately 10% of the cases were estimated as possible male with currently no DNA confirmation.…”

“…They have shown that this high level of heterogeneity in ancestry proportions exists at any geographic partitioning, from the microregional (e.g., central Mexico) , to the national , and even at the international scale. Furthermore, genetic and craniometric evidence attests that ancestry composition is geographically structured in Latin American . For example, in Mexico, European ancestry decreases along a north‐to‐south cline, while Native American ancestry increases concomitantly along the same cline .…”

“…The study of morphological variation in the cranium is a cornerstone of skeletal population analyses, with standard interlandmark distance (ILD) measurements, that is, traditional craniometric data, providing adequate information for revealing population structure and, in turn, speaking to population histories at various levels of specificity . In terms of their information on biogeographic ancestry, craniometrics can capture both broad continental variation that may reflect our evolutionary history, and the more nuanced regional variation that may signal recent micro‐evolutionary processes, such as admixture events .…”

“…As such, craniometrics are an integral part of how researchers have come to understand both the complex origins, settlements, migrations, and gene flow of populations inhabiting Latin America over thousands of years as well as the introduction of European colonizers and enslaved populations from West Africa in its more recent history . The complex histories of Latin Americans, both pre‐ and postcolonization, are reflected in the heterogeneous cranial morphology present in Latinos today, whose ancestral compositions often reflect parental contributors from two or more continents (Americas, Europe, and Africa) .…”

“…Furthermore, genetic and craniometric evidence attests that ancestry composition is geographically structured in Latin American . For example, in Mexico, European ancestry decreases along a north‐to‐south cline, while Native American ancestry increases concomitantly along the same cline . Continental ancestry estimates are only one approach to parental modeling of population variation and usually do not capture nuanced regional or local population‐specific variations.…”