One of the big questions concerning the transition from foraging to farming is how this transition impacted workload: did farming offer a relief from the constant quest for food or did it impose a heavier burden on those now responsible for its production? Answers to these questions lie in the study of the skeletal changes associated with mechanical stresses: degenerative joint disease and structural changes in bone morphology - an area of study known as biomechanics. Degenerative joint disease (osteoarthritis) refers to destructive changes of joint surfaces that primarily occur in response to mechanical stress and physical activity, although other contributing factors such as age, sex, and weight also play a role in the development and severity of joint damage. Biomechanics refers to the application of engineering principles to the study of living tissue; in other words, the functional properties of bone are understood in terms of the same loading modes that affect steel beams and other building materials (e. g., tension, compression, bending, sheer, torsion). These two indices account for the majority of studies focused on changes in workload with agriculture, although there is growing interest in a third method involving study of muscle attachment sites (musculoskeletal markers, or MSMs).
Degenerative Joint Disease as an Indicator of Workload and Activity Patterns
Comparative studies of degenerative joint disease are more limited than other types of studies described above, but those available have generally documented a decline in osteoarthritis in both New and Old World settings with the transition to agriculture.
In western Europe, for example, Mesolithic samples tend to show more osteoarthritis - particularly in the back and upper limbs - than Neolithic samples, suggesting that foragers experienced greater biomechanical stress than later farmers. In North America and particularly in the Southeast, where many of these studies have been conducted, osteoarthritis has been shown to decline in a number of joint surfaces with this economic transition. In Alabama and the Georgia Bight, declines are evident in the bones of the neck and lower back, the elbows, and knee joints. Within the Georgia Bight, the skeletal remains of upland agriculturalists show more osteoarthritis than those of lowland agriculturalists, suggesting that topography influenced workload, and thus the mechanical stresses placed on the joints of agriculturalists living in this region. Several studies from the American Southeast also document a shift to greater sexual dimorphism in the severity and patterning of osteoarthritis with the transition to agriculture, as well as a tendency for males to be more affected than females. These data imply that, although workload or at least mechanical loading of joints may have declined overall, the sexual division of labor became more pronounced with food production.
There are exceptions to this pattern of decline in osteoarthritis, however. In Portugal, Mesolithic foragers show few signs of osteoarthritis, whereas several severe cases are present in a sample of Neolithic farmers, particularly in the bones of the neck - perhaps from carrying heavy loads on the head. At the Dickson Mounds site in Illinois, degenerative joint disease (DJD) increased in the vertebras with agricultural intensification in comparison to earlier agriculturalists, indicating that changes in the intensity of production could result in rising prevalence of osteoarthritis. These cases once again illustrate the variability that exists in samples classified as agriculturalists.
Biomechanical Measures of Workload and Activity Patterns
Studies of biomechanical properties of long bones provide an independent means of assessing workload and activity patterns, and have often been used in conjunction with patterns of osteoarthritis. Crosssectional geometry is arguably the most accurate method for identifying activity-based changes from bone morphology, although external measurements have also produced useful results. In cross-sectional geometry, cross-sectional data on bone mass and distribution relative to the long axis of a bone are obtained from computed tomography images or actual cross sections of bone. These measurements provide insights into mechanical loading of bones and therefore types and levels of physical activity. Much of the data currently available derive from studies of North American samples, and indicate that bone mass and distribution differed between prehistoric foragers and farmers, but not always in predictable ways. In Georgia Bight populations, for example, the transition to agriculture was accompanied by a decline in bone strength (and thus, mechanical loading), whereas in northwestern Alabama bone strength increased with agriculture. Emerging research on European populations has documented a decline in bending and torsional strength of femurs and tibias with the Neolithic transition, a pattern consistent with many American agriculturalist samples and one supporting archaeological evidence that mobility declined with the transition to agriculture.
Studies of cross-sectional geometry in North American samples also indicate that men and women did not always experience this economic transition equally in terms of workload. Male foragers, for example, tend to have greater torsional strength of the femur midshaft (larger midshaft diameters) than male agriculturalists, whereas females show no consistent difference according to subsistence strategy. These data suggest that the decline in mobility evident with food production is particularly reflective of changes in the activities of men. Women, on the other hand, tend to have structural properties that correlate with ruggedness of the local terrain, supporting the hypothesis that women in both contexts were more tethered to the home base and domestic tasks performed there. The humeri of agriculturalists also show sex differences in structural properties that appear to reflect distinct gender roles. Samples from prehistoric Alabama and Georgia Bight populations generally show a decline in left/right asymmetry with agriculture, but this pattern is particularly evident for females. One likely explanation is an increasing emphasis on two-handed tasks such as maize pounding and grinding that were habitually performed by women.
These examples document the variable impacts that the transition to agricultural production could have on different members of the same society. They illustrate another aspect of the complexity that emerges when attempts are made to characterize the biological impacts of agriculture in a broad comparative manner.
World History
