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Cranial morphological distribution of African descent peoples as reflectors of migration, variation, and race construction
Abstract
The Trans-Atlantic slave trade instigated systemic rupture that resulted in the widespread geographical and cultural dispersal of peoples of African descent, known as the African diaspora. These patterns of forced migration have also impacted genetic distribution, demonstrated in the morphological diversity in historic skeletal collections. This study utilized 3D geometric morphometric methods to assess distributions of cranial morphology from individuals representing enslavement and post-emancipation periods in the Caribbean United States, and South Africa. The dataset included over 100 individuals of documented African descent, including 66 individuals from the Smithsonian’s Robert J. Terry Anatomical Skeletal Collection, as well as over 30
individuals from the University of Pennsylvania’s ORSA CT scan database and Newton Plantation, Barbados.
Fixed landmark and sliding semilandmark data were collected from each individual cranium using a MicroScribe for physical remains and Amira software for CT scans. The data were aligned with a generalized Procrustes superimposition, and the coordinates were tested with PCA, ANOVA, and permutation analyses. Geographic origin by country and local region had significant effects on shape in the full dataset; local region
exhibited higher R-squared values than country. The PCA analysis attributed 10% of variance to the PC1 axis and 9% to PC2. Pre-emancipation individuals generally had higher PC1 and PC2 scores, but all three regions shared considerable overlap. These results suggest that while geography impacts biological distribution, particularly on the local level, these distinctions are not exclusive. More broadly, these preliminary findings
reflect the continual redrawing of racial categories that inform current dialogues on diversity.
Bioarchaeological analysis of human remains from St Hilda’s Church cemetery, South Shields was undertaken to investigate ancestral diversity in post-medieval Britain. Methodological evaluations argue that when diversity is explored through phenotypic traits, biological affiliations are best investigated through dental morphology due to its resistance to exogenous influences, whereas cranial form appears to be increasingly influenced by environmental and cultural factors in the post-medieval period. A novel quantitative model was developed for a within-group analysis of dental morphology assessed through the Arizona State University Dental Anthropology System, successfully identifying an ancestral outlier. An osteobiographical narrative for this individual, combining osteological and historical data with social theory, suggests that personhood is malleable and multifaceted. Ancestry is therefore most appropriately understood as one aspect of identity which also included sex, occupation, social status and linguistic affiliation.
Quantitative shape analysis using geometric morphometrics is based on the statistical analysis of landmark coordinates. Many structures, however, cannot be quantified using traditional landmarks. Semilandmarks make it possible to quantify two or three-dimensional homologous curves and sur- faces, and analyse them together with traditional landmarks. Here we first introduce the concept of sliding semilandmarks and discuss applications and limitations of this method. In a second part we show how the sliding semilandmark algorithm can be used to estimate missing data in incomplete specimens.
Today there is a fully developed statistical toolkit for data that come as coordinates of named point locations or landmarks. Because all the statistical methods require these landmarks to be homologous among the specimens under investigation it is challenging to include information about the curves and surfaces in-between the landmarks in the analysis. The problem is that these correspond biologically as extended structures rather than lists of distinct points. This chapter is devoted to the method of semilandmarks (Bookstein, 1997), which allows these homologous curves and surfaces to be studied with the existing statistical toolkit. Information from the interior of homogeneous tissue blocks is not accessible by these methods. An earlier morphometric practice uses some nonlandmark points from curves or surfaces as if they were landmarks: the extremal points (Type III of Bookstein, 1991) that have definitions like “most anterior” or “widest point.” These locations, however useful for traditional distance measurements, are ambiguous
This paper reviews some of the important properties of geometric morphometric shape variables and discusses the advantages and limitations of the use of such data in studies of phylogeny. A method for fitting morphometric data to a phylogeny (i.e., estimating ancestral states of the shape variables) is presented using the squared-change parsimony criterion for estimation. These results are then used to illustrate shape change along a phylogeny as a deformation of the shape of any other node on the tree (e.g., the estimated root of the tree). In addition, a method to estimate the digitized image of an ancestor is given that uses averages of unwarped images. An example dataset with 18 wing landmarks for 11 species of mosquitoes is used to illustrate the methods. [Keywords: squared-change parsimony, Procrustes, thin-plate spline, partial warps, mosquito wings, Culicidae] 2. Introduction The relatively new field of geometric morphometrics represents an important new paradigm for the ...
Objectives:
Through pathological and stable isotope analyses, this study probes the stressors, disease ecology, and diets of enslaved individuals from an antebellum plantation cemetery. The study aims to highlight how interindividual isotopic differences reveal that marginalization is not uniformly experienced or embodied.
Methods:
The cemetery population consists of 16 individuals; dental and skeletal pathological indicators were collected for all individuals, and light stable isotope ratios (δ(15) N, δ(13) C) were generated from the collagen and hydroxyapatite of nine individuals.
Results:
The analyzed individuals have high frequencies of enamel defects-similar to contemporaneous enslaved cemetery individuals-and particularly high frequencies of carious lesions. Skeletal analysis shows evidence of chronic conditions among several individuals, two of whom likely have tuberculosis. Although the sample size is small, stable isotope values display interesting trends: there is interindividual heterogeneity in δ(13) C values, and most subadults from the cemetery have lower δ(15) N and higher δ(13) C values than the sampled adults. These relationships can be tested with larger datasets and have the potential to reveal important information about slave foodways and the broader experience of enslavement.
Conclusions:
The results of this study suggest that racial discrimination, enslavement, and age do not fully account for the heterogeneity in degree of embodied stressors. There are likely other factors at play, intersecting with the aforementioned, that influenced the lived experience of slavery and the degree of marginalization.
Geometric Morphometrics for Biologists is an introductory textbook for a course on geometric morphometrics, written for graduate students and upper division undergraduates, covering both theory of shape analysis and methods of multivariate analysis. It is designed for students with minimal math background; taking them from the process of data collection through basic and more advanced statistical analyses. Many examples are given, beginning with simple although realistic case-studies, through examples of complex analyses requiring several different kinds of methods. The book also includes URLâs for free software and step-by-step instructions for using the software.
Past studies have revealed that much of human craniometric variation follows a neutral model of population relationships. At the same time, there is evidence for the influence of natural selection in having shaped some global diversity in craniometrics. In order to partition these effects, and to explore other potential population-specific influences, this article analyzes residuals of craniometric distances from a geographically based neutral model of population structure. W.W. Howells' global craniometric data set was used for these analyses, consisting of 57 measurements for 22 populations around the world, excluding Polynesia and Micronesia because of the relatively recent settlement of these regions. Phenotypic and geographic distances were derived between all pairs of populations. Three-dimensional multidimensional scaling configurations were obtained for both distance matrices, and compared using a Procrustes rotation method to show which populations do not fit the geographic model. This analysis revealed three major deviations: the Buriat, Greenland Inuit, and Peru. The deviations of the Buriat and Greenland Inuit appear to be related to long-term adaptation to cold environments. The Peruvian sample is more similar to other New World populations than expected based on geographic distance alone. This deviation likely reflects the evolutionarily recent movement of human populations into South America, such that these populations are further from genetic equilibrium. This same pattern is seen in South American populations in a comparative analysis of classical genetic markers, but not in a comparative analysis of STR loci, perhaps reflecting the higher mutation rate for the latter.
We report here on new data examining cranial variation in 18 modern human sub-Saharan African populations. Previously, we investigated variation within southern Africa; we now extend our analyses to include a series of Central, East, and West African crania, to further knowledge of the relationships between, and variation and regional morphological patterning in, those populations. The sample comprises 377 male individuals; the three-dimensional coordinates of 96 landmarks are analyzed using Procrustes-based methods. Interpopulation variation is examined by calculating shape distances between groups, which are compared using resampling statistics and parametric tests. Phenotypic variance, as a proxy for genetic variance, is measured and compared across populations. Principal components and cluster analyses are employed to explore relationships between the populations. Shape differences are visualized using three-dimensional rendered models. Observed disparity patterns imply a mix of differences and similarities across populations, with no apparent support for genetic bottlenecks, which is likely a consequence of migrations that may have influenced differences in cranial form; supporting data are found in recent molecular studies. The Pygmy sample had the most distinctive cranial morphology; characteristically small in size with marked prognathism. These features characterized, although less strongly, the neighboring Bateke, and are possibly related to similar selective pressures in conjunction with interbreeding. Small cranial size is also involved in the considerable distinctiveness of the San and Khoikhoi. The statistical procedures applied in this study afford a powerful and robust means of quantifying and visualizing the magnitude and pattern of cranial variation between sub-Saharan African populations.
Natural selection for electrolyte conservation has likely been the norm throughout human evolutionary history. However, the current patterns of excessive dietary salt intake create the potential for salt overload. Under these conditions, hypertension may be considered an expected pathological response to an evolutionarily new constraint. The transatlantic Middle Passage may have created a genetic bottleneck for salt conservation in African-Americans. Although the initial consequences of this important historical event probably constricted genetic variability and further magnified the potential for salt-sensitive hypertension, the Middle Passage undoubtedly also served as a more generalized major source of environmental stress and may have stimulated subsequent hereditary diversity in the survivors of this holocaust and their descendants. Accelerated rates of mutation, genetic recombination, and transposable genetic elements in conjunction with enhanced opportunities for gene flow, new selective pressures, and drift have all contributed to the tremendous heterogeneity of contemporary African-Americans. It is unlikely that a single genetic event, even of the severity of the Middle Passage, can account comprehensively for the apparent susceptibility of this macroethnic group to high blood pressure and hypertension.
Migration is expected to affect craniometric variation in three ways: 1) movement into a different environment leading to developmental plasticity; 2) movement into a different environment followed by in situ adaptation through natural selection; and 3) changes in among-group differentiation and genetic distance through the action of gene flow. The relative influence of these three factors has been argued in the literature, most recently in a series of articles debating the statistical and biological significance of Boas's immigration studies as they relate to cranial plasticity. The Boas debate is discussed within the broader context of debate over genetic and environmental influences on craniometric variation. Additional examples are provided from an ongoing study of global craniometric variation. Although developmental plasticity and climatic adaptation have had an impact on craniometric variation, these factors tend not to erase, or even obscure greatly, underlying patterns of population structure and history that fit a neutral model of quantitative variation. Thus, craniometric data can be used to explore questions of gene flow and genetic affinity.
Cranial morphology is widely used to reconstruct evolutionary relationships, but its reliability in reflecting phylogeny and population history has been questioned. Some cranial regions, particularly the face and neurocranium, are believed to be influenced by the environment and prone to convergence. Others, such as the temporal bone, are thought to reflect more accurately phylogenetic relationships. Direct testing of these hypotheses was not possible until the advent of large genetic data sets. The few relevant studies in human populations have had intriguing but possibly conflicting results, probably partly due to methodological differences and to the small numbers of populations used. Here we use three-dimensional (3D) geometric morphometrics methods to test explicitly the ability of cranial shape, size, and relative position/orientation of cranial regions to track population history and climate. Morphological distances among 13 recent human populations were calculated from four 3D landmark data sets, respectively reflecting facial, neurocranial, and temporal bone shape; shape and relative position; overall cranial shape; and centroid sizes. These distances were compared to neutral genetic and climatic distances among the same, or closely matched, populations. Results indicate that neurocranial and temporal bone shape track neutral genetic distances, while facial shape reflects climate; centroid size shows a weak association with climatic variables; and relative position/orientation of cranial regions does not appear correlated with any of these factors. Because different cranial regions preserve population history and climate signatures differentially, caution is suggested when using cranial anatomy for phylogenetic reconstruction.
Evolutionary investigations of human crania typically take a limited view of cranial diversity as they discount the possibility that human cranial variation could simply be due to the effects of random genetic drift, gene flow and mutation in favor of natural selection and developmental changes. Natural selection alone cannot explain similarities between patterns of cranial and molecular diversity observed in humans. It appears that the amount of phenotypic variance in the human cranium decreases at the population level as a function of distance from Sub-Saharan Africa much in the same way as observed for human molecular data.
African Diaspora in the Americas. Encyclopedia of Diasporas: Immigrant and Refugee Cultures Around the World
- K A Yelvington
Yelvington, K. A. (2005). African Diaspora in the Americas. Encyclopedia of Diasporas:
Immigrant and Refugee Cultures Around the World, 24-35.
Catalogue of skulls of man and the inferior animals
- S G Morton
Morton, S. G. (1849). Catalogue of skulls of man and the inferior animals, in the collection of
Samuel George Morton. Merrihew & Thompson, Prtrs.
The Anthropological Treatises of Johann Friedrich Blumenbach
- J F Blumenbach
- T Bendyshe
- K Marx
- P Flourens
- R Wagner
- J Hunter
Blumenbach, J. F., Bendyshe, T., Marx, K., Flourens, P., Wagner, R., & Hunter, J. (1865). The
Anthropological Treatises of Johann Friedrich Blumenbach... Anthropological Society.
Sliding semi-landmarks on symmetric structures in three dimensions
- S Schlager
Schlager, S. (2012). Sliding semi-landmarks on symmetric structures in three dimensions. Am. J. Phys.
Anthropol, 147, 261.
A response to George Armelagos
- F L Jackson
Jackson, F. L. (2005). A response to George Armelagos' commentary. Transforming
Anthropology, 13(2), 125-135.