Crural Indices in Neandertals and Modern Humans: Implications for Limb Proportions, Environment, and Body Size Variation

Abstract

This dissertation investigates the functional and adaptive significance of Neandertal limb morphology by integrating comparative anatomy, biomechanical modeling, and methodological validation. The crural index (CI)— a ratio of tibial to femoral length— served as a key metric for exploring thermoregulatory and terrain-related adaptations.In Chapter 3, CI values were analyzed across 21 modern human populations and multiple Neandertal individuals. Neandertals exhibited lower average CIs than modern humans, consistent with cold-adapted body forms, but fell within the observed range of modern variation. Chapter 4 modeled center of mass (CoM) shifts on sloped terrain and found that Neandertal limb proportions and trunk morphology produced a lower and more posterior CoM than in modern humans. These differences became more pronounced on inclines, suggesting biomechanical advantages for locomotion in rugged environments. Chapter 5 validated the use of external anatomical landmarks to estimate skeletal limb lengths using CT data from over 100 individuals. While femoral and tibial lengths showed strong agreement between external and skeletal measurements (R² > 0.97), crural index values derived from external landmarks exhibited only moderate correlation (R² = 0.60), highlighting limitations in ratio-based proxies. Together, these findings support a multifactorial model of Neandertal adaptation involving both climatic and biomechanical selective pressures. They also emphasize the importance of methodological rigor when using external measurements in evolutionary analyses. This work contributes a refined framework for interpreting postcranial morphology in both fossil and modern human populations.