Variation in human rib and femoral histology: A study of ancient and modern humans

Abstract

Remodelling is a process of bone renewal occurring throughout the human lifespan. Remodelling evidence is retained in bone microstructure (histology) in modern and ancient samples, providing a rich source of knowledge about human health and behaviour. However, we do not fully understand how age, biological sex, social status, and anatomical form of bones, influence human femoral and rib histology, particularly in Australia. To date, only one study examined Australian human femoral and rib histology, but none have compared Australian to medieval British samples to explore ancestral indicators of remodelling. This thesis aimed to investigate how different factors influence human rib and femoral histology, particularly in largely unexplored modern Australian samples compared to medieval British samples as a more widely studied ancestral population. Four questions were identified: (1) does human rib and femoral bone histology vary with age, sex and social status in samples of English ancestry?; (2) do modern and medieval human bone histology comparisons indicate more sedentary modern lifestyle? (3); is there variation in histological variables between serial rib sections? (4); does cortical bone histology vary in the femur and rib with distinct bone metabolic activities? The methods in this thesis were bone histomorphometry and cross-sectional geometry, where secondary osteons, Haversian canals, porosity, and cortical bone were quantified and analysed using univariate and multivariate statistics. The first thesis question found that secondary osteon densities were higher in older than middle adults in the rib, but not in the femur. Females had higher rib and femoral osteon and Haversian canal area than males. Modern ribs had higher secondary osteons densities than the medieval samples, except for the anterior femur, where this applied only to modern versus medieval low status. Rib porosity was higher in medieval low status samples, except in the anterior femur where it was higher in modern samples. Modern samples had lower rib cortical width than medieval samples. For thesis question two, a discriminant function analysis based on multivariate comparisons successfully separated medieval and modern rib and femoral bone, but there was no conclusive evidence that modern humans were more sedentary than medieval humans. Results from analyses addressing thesis question three found that there were correlations between serial pairs of rib cross-sections in most histological variables, except porosity and osteon and Haversian canal densities, suggesting that sampling ribs in different shaft areas may render different histological results depending on variables observed. For the final thesis question four it was discovered that femoral secondary osteons and Haversian canals were larger than in the rib, but they did not necessarily vary in shape, though nuances in the shape variables used were evident. A reduced major axis regression determined secondary osteon and Haversian canal isometry in the rib but positive allometry in the femur, suggesting different constraints in secondary osteon formation. This thesis concludes that bone histology, a product of remodelling, is in a complex relationship with age, sex, and social status (determining diet, health and access to resources) and that it changes depending on whether the femur or rib are investigated, and also on the rib sectioning location. It appears that rib and femur remodelling in modern Australia has remained similar to English medieval times. However, there is an allometric constraint on histology, which means that future rib and femur studies should account for bone size when examining histology. These results suggest that rib and femoral microstructure is influenced differently by different factors. This thesis is the first comprehensive study of bone histology applying multivariate and allometric analyses that includes modern Australian alongside medieval English samples. Show more