No abstract

Increased sedentism during the Holocene has been proposed as a major cause of decreased skeletal robusticity (bone strength relative to body size) in modern humans. When and why declining mobility occurred has profound implications for reconstructing past population history and health, but it has proven difficult to characterize archaeologically. In this study we evaluate temporal trends in relative strength of the upper and lower limb bones in a sample of 1,842 individuals from across Europe extending from the Upper Paleolithic [11,000-33,000 calibrated years (Cal y) B.P.] through the 20th century. A large decline in anteroposterior bending strength of the femur and tibia occurs beginning in the Neolithic (∼4,000-7,000 Cal y B.P.) and continues through the Iron/Roman period (∼2,000 Cal y B.P.), with no subsequent directional change. Declines in mediolateral bending strength of the lower limb bones and strength of the humerus are much smaller and less consistent. Together these results strongly implicate declining mobility as the specific behavioral factor underlying these changes. Mobility levels first declined at the onset of food production, but the transition to a more sedentary lifestyle was gradual, extending through later agricultural intensification. This finding only partially supports models that tie increased sedentism to a relatively abrupt Neolithic Demographic Transition in Europe. The lack of subsequent change in relative bone strength indicates that increasing mechanization and urbanization had only relatively small effects on skeletal robusticity, suggesting that moderate changes in activity level are not sufficient stimuli for bone deposition or resorption. mobility | Europe | Neolithic | bone strength

Captive and wild G. gorilla follow different ontogenetic trajectories in long bone diaphyseal shape, corresponding to environmental differences and subsequent modified locomotor behaviors. Differences related to phylogeny are most evident early in development.

Objectives: While many attempts have been made to estimate body mass in hominins from lower limb bone dimensions, the upper limb has received far less attention in this regard. Here we develop new body mass estimation equations based on humeral articular breadths in a large modern human sample and apply them to 95 Plio-Pleistocene specimens. Materials and Methods: Humeral head superoinferior and total distal articular mediolateral breadths were measured in a morphologically diverse sample of 611 modern human skeletons whose body masses were estimated from bi-iliac breadth and reconstructed stature. Reduced major axis regressions were used to compute body mass estimation equations. Consistency of the resulting estimates with those derived previously using lower limb bone equations was assessed in matched Plio-Pleistocene individuals or samples. Results: In the modern reference sample, the new humeral body mass estimation equations exhibit only slightly lower precision compared to the previously derived lower limb bone equations. They give generally similar estimates for Pleistocene Homo, after accounting for the different shape of the humeral head articular surface in archaic Middle and Late Pleistocene Homo, except for distal humeral estimates for Late Pleistocene specimens, which average somewhat below lower limb estimates. Humeral equations give body mass estimates for australopiths that appear much too high, except for Australopithecus sediba. A chimpanzee-based distal humeral articular formula appears to work well for larger australopith specimens. Discussion: The new formulae provide a more secure foundation for estimating hominin body mass from humeri than previously available equations.

Bone loss and heightened fracture risk are common conditions associated with ageing in modern human populations and have been attributed to both hormonal and other metabolic and behavioural changes. To what extent these age-related trends are specific to modern humans or generally characteristic of natural populations of other taxa is not clear. In this study, we use computed tomography to examine age changes in long bone and vertebral structural properties of 34 wild-adult Virunga mountain gorillas ( Gorilla beringei beringei ) whose skeletons were recovered from natural accumulations. Chronological ages were known or estimated from sample-specific dental wear formulae and ranged between 11 and 43 years. Gorillas show some of the same characteristics of skeletal ageing as modern humans, including endosteal and some periosteal expansion. However, unlike in humans, there is no decline in cortical or trabecular bone density, or in combined geometric-density measures of strength, nor do females show accelerated bone loss later in life. We attribute these differences to the lack of an extended post-reproductive period in gorillas, which provides protection against bone resorption. Increases in age-related fractures (osteoporosis) in modern humans may be a combined effect of an extended lifespan and lower activity levels earlier in life. This article is part of the theme issue ‘Evolution of the primate ageing process'.