Monday 27 October 2014

Assessing the lifestyles of Later Stone Age herders in the Orange River Valley of South Africa using their long-bone morphology.

The term Later Stone Age is used in South Africa to describe Holocene stone tool making cultures dating from about 10 000 years ago until the historical era. From the 1990s onwards efforts have been made to understand the lifestyle of Later Stone Age hunter-gatherers living in fynbos and temperate rainforest conditions by studying the morphology of long-bones (arm and leg bones) from archaeological sites. These bones are highly prone to modification during an individual’s lifetime, as they serve as supports and anchors for the limb muscles used in physical activity, and the body is capable of modifying the bone structure to provide support for repeated activity.

These studies have suggested that both male members of both populations had strong lower limbs, suggesting that they led very mobile lives - it was notable that the fynbos individuals were as robust in their lower limb strength despite the forest individuals living in much more hilly terrain. However lower limb bones were more developed in forest females than fynbos females, suggesting that terrain did play a role; both sexes had well developed lower limbs in forest populations, whereas the fynbos population was sexually dimorphic (i.e. the sexes were different), with males more robust than females.

The upper limbs were more developed in males in both populations, suggesting more physical activity was being undertaken by the males than the females. The males also showed asymmetry of the upper limb-bone development, this being slight in the fynbos males but quite pronounced in the forest males. It has been suggested that this asymmetry may reflect the different hunting methods of the two groups, with the forest hunters favouring spears (thrown with one hand) while those living on the fynbos preferred light bows (where both hands are used to hold the bow and draw the string). This has been supported by studying the limbs of modern athletes, tool assemblages from the two regions, and records of living San hunters living in the two areas.

The results of these studies have subsequently been used as a base to compare to other small-bodied Holocene hunter-gatherer populations in the Andaman Islands, Tierra Del Fuego and Australia. These studies found that the Andaman Islanders and Yahgan foragers of Tierra Del Fuego showed considerably higher upper limb-bone development that either South African population, consistent with a more aquatic lifestyle that involved frequent swimming and canoeing, while the Australian Aboriginal skeletons showed less development in both upper and lower limbs, which has been suggested to be indicative of a lifestyle involving considerably more foraging, at the expense of other activities.

In a paper published in the South African Journal of Science on 22 September 2014, Michelle Cameron of the Department of Archaeology andAnthropology at the University of Cambridge and the Department of Anthropology at the University of Toronto and Susan Pfeiffer of the Department of Anthropology at the University of Toronto and the Department of Archaeology at the University of Cape Town describe the results of a study of the limb bones of a new group, Later Stone Age herders from the Orange River Valley of South Africa.

Map of southern Africa with forest, fynbos and lower Orange River Valley regions approximated. The fynbosregion is indicated by the solid outline, the forest region by the small dotted outline and the lower Orange River Valley by the dashed outline. Black lines indicate approximate latitude markers and the star indicates the approximate location of Koffiefontein. Cameron & Pfeiffer (2014).

The bones used in the study came from burials at Koffiefontein and Augrabies Falls, both are thought to date from around the beginning of the historical period in South Africa, with the Koffiefontein burial dated to about 390 years ago (i.e. about 1620). The bones are thought to have come from small bodied herder-foragers, belonging to the same San ethnic group as the coastal population, and also reliant on stone-aged technologies, though this population is thought to have had contact with other ethnic groups using different technologies, and is likely to have had some degree of genetic and technological exchange. The Orange River Valley has a seasonally arid climate, with vegetation intermediate between the Sweet Grassveld and Karoo types.

The inland hunter-foragers were found to have higher upper limb strength than the coastal populations. This is contrary to predictions, since it was presumed that herding would reduce the need for intense upper limb activity compared to hunting. This increased strength was seen in both male and female herders (whereas in the other populations the males had higher upper limb strengths), and Cameron and Pfeiffer suggest that this may be linked to increased effort going into foraging in a semi-arid environment where there was competition with other groups (such as farmers who supplemented their livelihoods by some foraging).

Both sexes showed some upper limb asymmetry in the Orange River population. This was less than seen in males from the forest population, but greater than seen in males from the fynbos population. The cause of this is unclear, but it is thought to be unrelated to hunting, suggesting that foraging activity can play a greater role in the development of upper limb-bone asymmetry than previously thought.

The Orange River Valley population showed a similar level of lower sexual dimorphism to the fynbos population, with well developed, robust lower limbs in the males but not the females. This suggests a similar division of mobility-related labour between the two populations, but does not give any insight as to what it was. It was previously assumed that the fynbos males were travelling further afield than the females in pursuit of game, but this is less likely to have been the case amoung pastoralist herders, where the entire community is assumed to have moved with the herds.

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