The impact of footwear on human talar trabecular architecture.

The evolution of habitual bipedalism was a defining milestone in human history, yet fossil evidence indicates substantial variation in how bipedality was practiced. Trabecular bone, which responds throughout life to joint loading and orientation, offers a powerful way to investigate these differences. Interpreting variation in fossil hominins, however, requires a reliable baseline of intraspecific variation in modern humans, accounting for differences in lifestyle, mobility, and habitual behaviors. Many modern skeletal collections derive from postindustrial populations whose activity patterns, footwear use, and health profiles differ markedly from past populations, potentially biasing interpretations. Thus, habitually shod, postindustrial humans may not be the best proxy for the loading environments experienced by early hominins, whereas unshod individuals provide a closer approximation of barefoot locomotion. To explore the effects of footwear on internal bone structure, we examined trabecular architecture in the talus of habitually shod (N = 40) modern humans (Homo sapiens) from recent donation-based skeletal collections and habitually unshod (N = 16) individuals from the Andaman Island, Khoisan, and Aka populations, representing diverse ecological and subsistence contexts, using high-resolution micro-computed tomographic scans. Trabecular parameters-including bone volume fraction (BV/TV), relative BV/TV (rBV/TV), trabecular thickness (Tb.Th), separation (Tb.Sp), number (Tb.N), and degree of anisotropy (DA)-were quantified using canonical holistic morphometric analysis (cHMA). Shod individuals exhibited higher mean BV/TV and greater variability in BV/TV, suggesting that the talus remains heavily loaded due to its central role in weight bearing during bipedal gait, and that different types of footwear create variable force distributions across the ankle. The spatial distribution of rBV/TV revealed further differences between the groups: shod individuals showed higher rBV/TV in the medial and posterior talus, consistent with more dorsiflexed and medially loaded ankle postures, whereas unshod individuals had elevated rBV/TV in the talar head and neck, potentially reflecting loading associated to squatting or climbing. Shod individuals also exhibited higher mean DA indicating more strongly organized and directionally constrained trabeculae. Mean BV/TV was likewise higher in the shod group and primarily driven by greater trabecular thickness, as trabecular separation and number were broadly similar between groups, suggesting loading differences associated with footwear primarily influence BV/TV and trabecular anisotropy. By establishing clear patterns of trabecular variation between shod and unshod modern humans, this study provides a robust comparative framework for interpreting locomotor behavior in fossil hominins, while highlighting the need to further disentangle the effects of footwear from differences in body size, stature, subsistence strategy, and other aspects of lifestyle among human populations. Recognizing how habitual behavior influences internal bone architecture is essential for reconstructing past movement patterns and understanding the evolutionary pathways of bipedalism.