The Potential for Discrepancies in Population History Signatures from Different Segments of the Human Skeleton
Authors: Mallard Angela M. , Auerbach Benjamin M. 
Published: April 2020

The use of metric data from skeletal remains to assess models of evolutionary processes is a well‐established substitute for genomic data. However, it has been suggested in previous research that certain osteological elements retain population history signatures better than others because they are likely less subject to natural selection. This study examines the potential for differences in gene flow models using human crania (traits shown to evolve through neutral processes) versus postcrania (traits provisionally shown to have evolved in response to selection). In this study, we sampled from four large pueblos in the American Southwest representing a short temporal period and small geographic area (Arizona, c. 1200–1400, N=267). Based on a robust archaeological record detailing changes in material culture, researchers hypothesize immigration into this region from non‐local populations.

The study uses gene flow models based on variance comparison methods developed by Relethford and Blangero. Metric data were analyzed using the R statistical environment and RMET 5.0, a program based on the Relethford‐Blangero statistics. Under a quantitative genetic model, gene flow results in higher‐than‐expected variance in a population, which RMET examines. Likewise, gene flow decreases the biodistance between populations sharing genes, and so these were compared through Mahalanobis D2 distances.

Cranial and postcranial dimensions generally result in different patterns of gene flow. Comparing residual phenotypic variances from the Relethford‐Blangero model, only one of the four sites presents the same pattern of gene flow between cranial and postcranial results. Biodistance analyses show that the Pueblo population that is the greatest distance remains consistent in both crania and postcrania, but which of the other three is closest changes between the two body regions. This incongruence has implications for local disparities in the variance and in the mean differences between aspects of morphology.

Either the upper or lower limb elements may be driving the discrepancies, as limb bones are shown to respond dissimilarly to selection on a global scale. We conducted analyses comparing results of the upper and lower limbs. The results indicate upper limb residual variances are higher, but only the lower limb matches the patterns observed in the overall postcranial analysis. Biological distance relationships are very similar between the limbs, though the lower limb data is closer in magnitude to the overall postcranial distance. It is possible that the lower limb is driving the variance results for the postcrania, a result that provisionally reflects the evolution of femoral traits in recent humans in response to neutral processes. This has implications for how we evaluate population history using phenotypic data, particularly considering which phenotypic data to employ.

Support or Funding Information

This research was partially funded by the University of Tennessee Department of Anthropology through a Kneberg‐Lewis Scholarship.