Temporal trends in postcranial robusticity within the genus Homo are explored by comparing cross-sectional diaphyseal and articular properties of the femur, and to a more limited extent, the humerus, in samples of Recent and earlier Homo. Using both theoretical mechanical models and empirical observations within Recent humans, scaling relationships between structural properties and bone length are developed. The influence of body shape on these relationships is considered. These scaling factors are then used to standardize structural properties for comparisons with pre-Recent Homo (Homo sp. and H. erectus, archaic H. sapiens, and early modern H. sapiens). Results of the comparisons lead to the following conclusions: 1) There has been a consistent, exponentially increasing decline in diaphyseal robusticity within Homo that has continued from the early Pleistocene through living humans. Early modern H. sapiens are closer in shaft robusticity to archaic H. sapiens than they are to Recent humans. The increase in diaphyseal robusticity in earlier Homo is a result of both medullary contraction and periosteal expansion relative to Recent humans. 2) There has been no similar temporal decline in articular robusticity within Homo--relative femoral head size is similar in all groups and time periods. Thus, articular to shaft proportions are different in pre-Recent and Recent Homo. 3) These findings are most consistent with a mechanical explanation (declining mechanical loading of the postcranium), that acted primarily through developmental rather than genetic means. The environmental (behavioral) factors that brought about the decline in postcranial robusticity in Homo are ultimately linked to increases in brain size and cultural-technological advances, although changes in robusticity lag behind changes in cognitive capabilities.

Agriculture has long been regarded as an improvement in the human condition: Once Homo sapiens made the transition from foraging to farming in the Neolithic, health and nutrition improved, longevity increased, and work load declined. Recent study of archaeological human remains worldwide by biological anthropologists has shown this characterization of the shift from hunting and gathering to agriculture to be incorrect. Contrary to earlier models, the adoption of agriculture involved an overall decline in oral and general health. This decline is indicated by elevated prevalence of various skeletal and dental pathological conditions and alterations in skeletal and dental growth patterns in prehistoric farmers compared with foragers. In addition, changes in food composition and preparation technology contributed to craniofacial and dental alterations, and activity levels and mobility decline resulted in a general decrease in skeletal robusticity. These findings indicate that the shift from food collection to food production occasioned significant and widespread biological changes in human populations during the last 10,000 years.

Structural characteristics of the femur are compared in preagricultural (2200 B.C.-A.D. 1150) and agricultural (A.D. 1150-1550) subsistence strategy groups from the Georgia coast. Using an automated technique, cross-sectional geometric properties used in structural analyses (areas, second moments of area) were determined at midshaft and distal to the lesser trochanter in 20 adults from each group. A significant decline in magnitude of almost every geometric property occurs in the agricultural group. The differences between groups are reduced but still significant for many properties after standardizing for bone length differences. In addition, a remodeling of the femoral cortex to one of relatively smaller medullary and subperiosteal diameter, as well as a more circular cross-sectional shape, is characteristic of agricultural femora. Thus, while the relative cross-sectional area of bone remains the same, the spatial distribution of bone area is different in the two groups. The results strongly suggest a relative reduction in mechanical loadings of the femur in the agricultural group, implying different levels and possibly types of activity involving the lower limb in the two groups. The data are also compared with similar data available for the Pecos Pueblo (agricultural) sample. The comparison indicates that types of activity may have been more similar in the two agricultural samples, but that general levels of activity were more similar in the Pecos Pueblo and Georgia coast preagricultural samples.

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