Q Archaeology
Right: A view of Kgopolwe – the archaeological site is in the foreground of the photograph. Image: Nikolaas van der Merwe Right below: An aerial view of the Kgopolwe archaeological site – home of African farmers 1 000 years ago. Image: Nikolaas van der Merwe
Human diets The application of stable carbon isotope measurements to the study of human diet came about more or less by accident. In 1970, Nikolaas van der Merwe was excavating a group of Iron Age sites at Phalaborwa – among these sites was Kgopolwe 3, at that time the oldest known Iron Age site in South Africa, occupied approximately 1 000 years ago. Van der Merwe found a human male skeleton in an ash heap, which seemed to be out of place for a number of reasons. The body had been, as Van der Merwe puts it ‘… rather casually disposed of, instead of being tightly flexed and buried under the floor of the owner’s hut, as is customary ▲ ▲
conversion of carbon dioxide to dicarboxylic acid, a four-carbon compound – the C4 photosynthetic pathway. The details of this pathway were then described in Australian sugarcane and shown to occur in several other species of grasses. This becomes particularly important to human diets because the staple cereals of the Americas and Africa are maize, sorghum and millet. Even more important was the discovery that the grass species that have Kranz leaf anatomy all have C4 photosynthesis. The CAM pathway (which stands for crassulacean acid metabolism) is found in succulents, such as cactus plants, or the plakkies and sour figs that are common in the Cape. This pathway, however, is of little interest in the study of prehistoric diets. What is important is the fact that C3 and C4 plants fractionate carbon isotopes in very different ways. Stable carbon isotopes as food tracers The first clue that stable carbon isotopes could be used as food tracers came from research on marine animals in 1964, when PL Parker noticed that marine animals cover the same range of isotopic values as the foods that they eat. We now know that the ‘isotopic signature’ of food is passed on to consumers. As this food is metabolised, the carbon isotopes may be fractionated yet again before they are stored in the tissues. This makes it possible to determine, for example, the proportion of C3 and C4 plants in the diet of a herbivorous animal. The sample material can be hair, skin, bone, meat or horn as long as the fractionation factor of the material is known. Essentially this means that living organisms are considered as carbon isotope separators so each tissue type has its own characteristic fractionation factor.
The skeletal remains of the eleventh-century inhabitant of an Iron Age village, excavated by Nik van der Merwe at Kgopolwe 3, near Phalaborwa, that posed an anthropological puzzle. Image: Nikolaas van der Merwe
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