Sexual dimorphism and biomechanical loading in occipital bone morphological variation.

We explore the contribution of biological sex and biomechanical activity from subsistence to occipital bone variation. Previous studies have used occipital bone traits to determine biological sex and identify ancestry to differing degrees of success. Biomechanical stress from variation in subsistence and gender-based divisions of labor could perhaps explain some of the noise in the signal for these grouping variables. To explore this possibility, we used metric (foramen magnum length and breadth, external occipital protuberance depth, lambda-inion length, bicondylar breadth) and nonmetric traits (general occipital form, presence of a nuchal crest, and nuchal line count). We collected original data and mined published data for our analysis using skeletal collections of Native American hunter-gatherers and horticulturalists, a historic military site, and contemporary study collections. We find that the foramen magnum area exhibits sexual dimorphism and is not influenced by subsistence, but the accuracy of sex estimation is only 71%, suggesting the chance of being correct at slightly more than two-thirds. All traits exhibited sex-based variation but only bicondylar breadth and lambda-inion metrics exhibited subsistence-based variation. Given the limited amount of variance explained by either sex or sex and subsistence, biomechanics may still play a role but not from the influence of subsistence practices in these datasets. Additional data from a wider array of skeletal samples, perhaps with known occupation, is warranted if we are to understand how occipital variation is shaped.

An 8000-year-old case of thalassemia from the Windover, Florida skeletal population.

Thalassemia is a congenital blood disorder which destroys red blood cells at a faster rate than can be produced, resulting in anemia. Historically, this disease is found more often in Old World populations, such as Middle Eastern and Southeast Asian. The earliest reported skeletal evidence of thalassemia comes from the eastern Mediterranean (Atlit-Yam) and is correlated with early agriculturalists' exposure to malarial parasites. While there have been virtually no skeletal reports of thalassemia in prehistoric Native American populations, among the individuals from the 8000-year-old hunter-gatherer site of Windover, Florida there is a single potential case of the disease. A female in her early 20's exhibits bilateral foreshortening of the humeri with indications of premature epiphyseal fusion. Both proximal humeri are medio-laterally compressed, the gleno-humeral joint surfaces exhibit medial deformation, and bones show expansion of the medullary cavity with increased cancellous bone growth. These characteristics have been reported as indicators of thalassemia in both clinical and archaeological contexts. Alternate diagnoses such as congenital dislocation or injuries during child birth are considered but fail to account for the full set of characteristics shown. Individual #76 may, therefore, represent the oldest reported case of thalassemia from a native North American skeletal population.