Morphological variation in human skeletons

The statement that pairs of individuals from different populations are often more genetically similar than pairs from the same population is a widespread idea inside and outside the scientific community. Witherspoon et al. [“Genetic similarities within and between human populations,” Genetics 176:351–359 (2007)] proposed an index called the dissimilarity fraction (ω) to access in a quantitative way the validity of this statement for genetic
systems. Witherspoon demonstrated that, as the number of loci increases, ω decreases to a point where, when enough sampling is available, the statement is false. In this study, we applied the dissimilarity fraction to Howells’s craniometric
database to establish whether or not similar results are obtained for cranial morphological traits. Although in genetic studies thousands of loci are available, Howells’s database provides no more than 55 metric traits, making
the contribution of each variable important. To cope with this limitation, we developed a routine that takes this effect into consideration when calculating ω. Contrary to what was observed for the genetic data, our results show that cranial morphology asymptotically approaches a mean ω of 0.3 and therefore supports the initial statement—that is, that individuals from the same geographic region do not form clear and discrete clusters—further questioning the idea of the existence of discrete biological clusters in the human species. Finally, by assuming that cranial morphology is under an additive polygenetic model, we can say that the population history signal of human craniometric traits presents the same resolution as a neutral genetic system dependent on no more than 20 loci.

Revisione del materiale scheletrico umano risalente all'età del Bronzo proveniente dalla Grotta di Cosa (Ansedonia, GR) e da Castelnuovo dell'Abate (Montalcino, SI) presenti nella Sezione di Antropologia e Etnologia del Museo di Storia Naturale di Firenze

Review of the human skeletal material dating back to the Bronze Age from Cosa Cave (Ansedonia, GR) and from Castelnuovo dell’Abate (Montalcino, SI) located in the Anthropology and Ethnology Section of the Natural History Museum of Florence

Shape analysis of the human orbital cavity is challenging due to several reasons. First, it is a smooth surface where only few anatomical landmarks can be identified. Second, data acquisition via CT-scanning is limited due to poor representation of the orbital walls caused by the so-called partial volume effect. The structure of the orbital walls can also lead to gray values differing from the rest of the bony tissue. Hence, automatic segmentations based on gray value thresholds will not include them in the segmentation and produce pseudoforamina in the segmented orbital walls.

In this study, a symmetric template mesh representing the orbital region was created. Forty-six landmarks were placed manually onto skull surfaces which were automatically segmented from CT-scans of 656 individuals of European (♀:n=164, ♂:n=164) and Chinese (♀:n=164, ♂:n=164) origin. A statistical model was computed on basis of the template mesh and semi-automatically matched onto the skull surfaces. This way, the defects in the representation of the orbital wall were interpolated. Next, 600 bilateral semi-landmarks, evenly distributed on the surface of the orbital cavity, were placed automatically on each individual. Procrustes analysis and principal component analysis were performed on these configurations. Shape variation depending on the factors sex and population affinity was analysed using the principal component (PC) scores of the PCs accounting for 98% of the total variance. The results indicate significant influence of population affinity and sex on orbital cavity shape with weak interaction between the two.

Rüdell, A. 2016. Shape variation of the human orbital cavity. In: Program of the 85th annual meeting of the American Association of Physical Anthropologists. American Journal of Physical Anthropology 159:277.

Objectives: Human sexual dimorphism is frequently assessed through skull and pelvic size and shape. Researchers suggest that climatic variation and the associated stress may be significant factors in sexual dimorphism's etiology. However, little research has specifically investigated climatic effects on nonmetric skeletal indicators of sex. To further appreciate the plasticity of human biology, a comparative study of standard skull and pelvic nonmetric sex indicators is presented. Methods: A Native Alaskan archeological sample (n = 104) and a component of the Terry collection (n = 99) represent populations originating from different climatic environments in recent history. These sex-balanced groups are compared through Tukey-Kramer's method and Greene's t-test to determine any variation in degree of sexual dimorphism within and between samples. Results: The results reinforce the complex and multifaceted relationship between climate and sexual dimorphism. The Terry sample demonstrated a greater degree of sexual dimorphism with statistically significant differences in robusticity of the mastoid process and nuchal crest compared with the Native Alaskans. A more "male" morphotype and reduced dimorphism are appreciated in the pelves of Native Alaskans than the Terry sample. Conclusions: This research highlights a reduction in sexual dimorphism in populations under greater climatic stress and contributes to the production of more accurate skeletal assessments in future investigations. Discussion of confounding factors suggest more research is necessary to untangle climate and human morphology's complex relationship. This study contributes to a greater appreciation of human biological plasticity, ecogeographic variation, and the evolution of modern human diversity.