Morphological variation of the early human remains from Quintana Roo, Yucatán Peninsula, Mexico: Contributions to the discussions about the settlement of the Americas.

The human settlement of the Americas has been a topic of intense debate for centuries, and there is still no consensus on the tempo and mode of early human dispersion across the continent. When trying to explain the biological diversity of early groups across North, Central and South America, studies have defended a wide range of dispersion models that tend to oversimplify the diversity observed across the continent. In this study, we aim to contribute to this debate by exploring the cranial morphological affinities of four late Pleistocene/early Holocene specimens recovered from the caves of Quintana Roo, Mexico. The four specimens are among the earliest human remains known in the continent and permit the contextualization of biological diversity present during the initial millennia of human presence in the Americas. The specimens were compared to worldwide reference series through geometric morphometric analyses of 3D anatomical landmarks. Morphological data were analyzed through exploratory visual multivariate analyses and multivariate classification based on Mahalanobis distances. The results show very different patterns of morphological association for each Quintana Roo specimen, suggesting that the early populations of the region already shared a high degree of morphological diversity. This contrasts with previous studies of South American remains and opens the possibility that the initial populations of North America already had a high level of morphological diversity, which was reduced as populations dispersed into the southern continent. As such, the study of these rare remains illustrates that we are probably still underestimating the biological diversity of early Americans.

Morphological variation among late holocene Mexicans: Implications for discussions about the human occupation of the Americas.

OBJECTIVES: Cranial morphology has previously been used to estimate phylogenetic relationships among populations, and has been an important tool in the reconstruction of ancient human dispersals across the planet. In the Americas, previous morphological studies support a scenario of people entering the Americas and dispersing from North America into South America through Meso America, making the Mexican territory the natural funnel through which biological diversity entered South America. MATERIALS AND METHODS: We explore the cranial morphological affinities of three late Holocene Mexican series, in relation to ancient and modern crania from North and South America, Australo-Melanesia, and East Asia. Morphological affinities were assessed through Mahalanobis Distances, and represented via Multidimensional Scaling and Ward's Linkage Cluster analysis. Minimum FST values were also calculated for each series. RESULTS: Our results show Mexican groups share morphological affinities with the Native American series, but do not cluster together as would be expected. The minimum FST estimates show between-group variation in the Americas is higher than the Asian or Australo-Melanesian populations, and that Mexican series have high between-group variance (FST = 0.124), compared to the geographically larger South America (FST = 0.116) and North America (FST = 0.076). DISCUSSION: These results show that the Mexican series share morphological affinities with the East Asian series, but maintains high levels of between-group variation, similar to South America. This supports the suggestion that the high phenotypic variation seen the Americas is not a result of its size, as it can be found in more constricted areas, such as the Mexican territory.

Comparability of multiple data types from the Bering Strait region: cranial and dental metrics and nonmetrics, mtDNA, and Y-chromosome DNA.

Different data types have previously been shown to have the same microevolutionary patterns in worldwide data sets. However, peopling of the New World studies have shown a difference in migration paths and timings using multiple types of data, spurring research to understand why this is the case. This study was designed to test the degree of similarity in evolutionary patterns by using cranial and dental metric and nonmetric data, along with Y-chromosome DNA and mtDNA. The populations used included Inuits from Alaska, Canada, Siberia, Greenland, and the Aleutian Islands. For comparability, the populations used for the cranial and molecular data were from similar geographic regions or had a shared population history. Distance, R and kinship matrices were generated for use in running Mantel tests, PROTEST analyses, and Procrustes analyses. A clear patterning was seen, with the craniometric data being most highly correlated to the mtDNA data and the cranial nonmetric data being most highly correlated with the Y-chromosome data, while the phenotypic data were also linked. This patterning is suggestive of a possible male or female inheritance, or the correlated data types are affected by the same or similar evolutionary forces. The results of this study indicate cranial traits have some degree of heritability. Moreover, combining data types leads to a richer knowledge of biological affinity. This understanding is important for bioarchaeological contexts, in particular, peopling of the New World studies where focusing on reconciling the results from comparing multiple data types is necessary to move forward.