Femur

A bone’s response to mechanical loading during life and its preserved morphology after death illustrate skeletal adaptation within an individual or population. Analyses have shown that the morphology of the lower limbs differ between modern, historic, and prehistoric human populations due to activity, types of terrain, and adaptation to diverse climates. However, not all analysed populations follow this pattern. This may indicate that the trend of change in skeletal parameters is still not clear. That is why, the use of complex statistical models can be helpful interpreting the functional adaptation of the lower limbs. In addition, investigation of human populations from other regions such as Eastern Europe, Western Asia, Africa and Australia may give new information about morphological diversity.
The main aim of the proposed study was to investigate variation in femoral cross-sectional indicator of robusticity ( J) between human populations due to different types of economy, regions and chronological periods using a comprehensive statistical model that allows simultaneous analysis of several variables. The sample consisted of 1,981 individuals from the Early Pleistocene to modern times, aged between 16 and 87 years, with no fractures or pathological changes of the lower limbs.
For each individual the following variables were collected: sex, age, date range, region, type economy, femoral biomechanical properties (%CA, J, Ix/Iy), average slope of the terrain and body mass. The human populations came from Europe, Africa, Asia and Australia. The major part of the data came from European Data Set [1] in turn, information about Pleistocene individuals was collected from literature. The biomechanical properties of Neolithic farmers from Poland, Iran, Australian aborigines and Medieval Polish farmers were calculated using Moment Macro (v. 1.4) [2].
Generalized linear model was used to test whether the difference in the robusticity of femur were due to spatial, temporal and biological variation. In the model, difference in polar second moment of area ( J) was the dependent variable and sex, age, date, region, type of economy, %CA, Ix/Iy and average slope of the terrain were independent covariates. The GLM was calculated for raw and standardized femoral biomechanical properties, respectively [3]. The model calculated for raw biomechanical properties showed that region, sex, age, %CA, Ix/Iy and some types of economy (farmers, hunter-gatherers, pastoralists, urban farmers and urban populations) explained most of the variation in the robusticity of the femur. Slightly different results were obtained for the second model which used standardized biomechanical properties. Genealogical data of the skeletal remains, sex, age, %CA, Ix/Iy and one type of economy (hunting-gathering) were significant predictor covariates.
The model based on standardised biomechanical properties showed that there was a slight temporal decline in the robusticity of femur from Pleistocene to modern times. Although, this trend should be analysed with cautions due to small sample size of individuals from the older periods. Interestingly, terrain shape did not explain the variation in polar second moment of area ( J) which means that individuals from mountainous terrain are not characterised by more robust femur than individuals from lowlands. Size and not standardised femoral property showed significant differences in sex and age.
In addition, the standardized robusticity of the femur was associated with hunting and gathering. It may mean that this type of economy requires more resistant lower limbs to bending and torsion than farming, pastoralism or life in urban areas. On the other hand, not standardized robusticity index also showed association with pastoralism, farming, and urban life. But, this may be a result of differences in body mass and proportions between hunter-gatherers and human populations using different types of economy.