Linking structural variability in long bone diaphyses to habitual behaviors: Foragers from the southern African Later Stone Age and the Andaman Islands

Abstract

The cross-sectional distribution of cortical bone in long bone diaphyses is highly responsive to mechanical loading during life, yet the relationship between systemic and localized influences on skeletal structure remains unclear. This study investigates postcranial robustness throughout the body among adults from two groups of foragers with different patterns and modes of mobility, to determine whether there is evidence for upper vs. lower body localization of skeletal robustness. The samples used for this comparison are from the southern African Later Stone Age (LSA; n = 65, male = 33, female = 28) dating from ca. 10,000 to 2,000 B.P., and 19th century indigenous Andaman Islanders (AI; n = 36, male = 17, female = 16). The LSA were highly mobile foragers who did not exploit offshore marine resources. In contrast, the AI had tightly constrained terrestrial, but significant marine, mobility. Geometric properties of cortical bone distribution in the diaphyses of the clavicle, humerus, femur, tibia, and first metatarsal are compared between the samples, providing a representation of skeletal robustness throughout the body. Multivariate ANOVA shows the AI to have significantly stronger clavicles and humeri, while the LSA femora, tibiae, and first metatarsals are stronger than those of the AI. These patterns, in which upper and lower limbs show biomechanical properties that are consistent with habitual behaviors, suggest localized osteogenic response. Although postcranial robustness appears to be correlated with overall limb function, the results suggest that more proximal elements within the limb may be more responsive to mechanical loading.

Gradual decline in mobility with the adoption of food production in Europe

“…Changes in bone shape of this kind strongly imply localized modeling/remodeling resulting from specific mechanical stimuli (20). Despite some partially contrary evidence in cursorial animals (43), which may be under special constraints (20), a number of both experimental and observational studies of humans support the association between preferential strengthening of the lower limb bones in the A-P plane and greater mobility (30,(34)(35)(36)(37)(38). Thus, our results imply a major reduction in mobility in both sexes beginning in the Neolithic.…”

“…For example, vigorous exercise in humans greatly increases bending strains in the tibia (32,33) and is associated with preferential strengthening in the direction of movement, i.e., running and jumping lead to increases in A-P/M-L strength (30,34,35). Increased A-P/M-L bending strength of the lower limb bones also characterizes more terrestrially mobile populations or subpopulations (36)(37)(38). Following this rationale, several previous studies have examined temporal trends in lower limb bone cross-sectional shape, as a proxy for mobility, within Late Pleistocene or Holocene archaeological samples, generally demonstrating declines in A-P/M-L (or maximum/minimum) rigidity or strength (39)(40)(41)(42).…”

Robustness of the whole Jomon femur shaft assessed by cross-sectional geometry

“…The analysis was conducted on ancient bone to which mechanical experiments were difficult to apply (Endo and Kimura, 1970). Previous reports were concerned mainly with one or two sections of the ancient long bones (Lovejoy and Trinkaus, 1980;Kimura and Takahashi, 1982, 1984, 1992Ruff et al, 1984Ruff et al, , 1993Brock and Ruff, 1988;Trinkaus et al, 1994Trinkaus et al, , 1998Ruff, 1995Ruff, , 1999Trinkaus and Ruff, 1996;Trinkaus, 1997Stock and Pfeiffer, 2001;Holt, 2003). The robustness of the ancient femur along the whole shaft has been reported in only a few papers, such as on the Pecos (Ruff and Hayes, 1983a, b), Neanderthal (Trinkaus and Ruff, 1989), and Minatogawa fossils (Kimura and Takahashi, 1992).…”

Phenotypic Plasticity of Climbing-Related Traits in the Ankle Joint of Great Apes and Rainforest Hunter-Gatherers

“…For example, tennis and baseball players, in addition to cricketers, exhibit bilateral asymmetry in some indices of forelimb robusticity (Jones et al 1977;Shaw and Stock 2009;Warden et al 2009), and rowers have more robust humeri than nonrowers (Weiss 2003). Such associations have allowed researchers to infer habitual use of watercraft among populations who exploit aquatic resources (Stock and Pfeiffer 2001) or habitual digging with sticks by Late Stone Age foragers (Stock and Pfeiffer 2004). Accordingly, we hypothesize that the foraging behaviors of rainforest hunter-gatherers induce loading patterns that could generate diagnostic skeletal correlates.…”