Skeletal Biology, Trace Element Analysis and Slavery: One From The Archives

Physical anthropology is a wide discipline. It contains many subfields ranging from paleoanthropology to human variation to forensic anthropology (which I was specializing in) to skeletal biology. Skeletal biology is concerned with uncovering prehistoric health and disease, demography (more properly paleodemography) diet and subsitence strategies and behavior. Skeletal biologists have created a wide variety of methods to get at this information. Two of the more interesting methods are trace element analysis and stable isotope analysis.

In trace element analysis human bone is analyzed for their content of any of several different trace elements. Stontium is the most common trace element used. In nature organisms take in strontium in inverse proportion to their trophic level, so that animals have less than plants. Herbivores take in more strontium than omnivores and omnivores more than carnivores. The idea is that the ammount of strontium can be calibrated against a scale and compared with the content in human bone. From their you should be able to tell something about the diet of prehistoric peoples. For example, it is a long standing truism that the nature and amount of burial goods are indicators of social status. The larger the number of grave goods, the higher the status. One anthropologist (Schoeninger 1979) studied the relationship between grave goods and strontium levels in the associated skeletons. Shoeninger found that those individuals with more grave goods (and hence higher social status) had lower levels of strontium in their bones than those without grave goods. Indicating the higher status individuals had greater access to animal protein.
Another avenue for examing the above types of questions is through stable isotope analysis. Two of the most commonly used elements in stable isotope analysis are carbon and nitrogen. Stable isotope analysis using carbon actually originated from radiocarbon research, when it was realized that maize gives younger dates than wood from the same site. Carbon occurs in three different isotopic forms: C 12, C 13 and C 14. Plants prefferentially incorporate C 12 into their tissues relative to C 13 so the ratio C13/C12 is greater in the atmosphere than in plants (somewhat counterintuitive but correct). There are two main photosynthetic pathways (a third – the CAM- occurs in cacti) through which carbon gets incorporated into plants. One pathway (C4) discriminates less against C 13 than the other (C 3). Consequently, the values are less negative. The idea here is that you can analyze the carbon values (actually called delta values) from the faunal and paleobotanical remains at a site and compare them with the carbon values from human bone found at the site and determine the types of animals and plants that were being incorporated into the diet. Finally, there is a difference in carbon delta values between terrestrial and marine organisms (although mainly in areas that lack plants with the C 4 pathway.
Another element frequently used in stable isotope analysis is nitrogen. Some plants take up nitrogen from the soil, while others get nitrogen directly from the atmosphere. Nitrogen content is measured in delta values as well and there is a difeerence in delta values of around 10 between those that fix nitrogen from the soil (higher delta value) and those that fix it from the atmosphere. Herbivores have a higher delta value than plants – but it depends on whether they are eating soil or atmospheric fixers. Carnivores, as you would expect have an even higher value. Finally, nitrogen can also be used to separate terrestrial and marine diets. One of the more interesting studies using nitrogen was that of Tuross et al 1989. Tuross and coworkers examined the fingernails of modern mothers and infants throughout the period of breastfeeding and weaning. Nursing infants showed higher nitrogen delta values than their mothers. The infant delta values fell to normal adult levels after weaning. This pattern has been found in cemetary groups and prehistoric populations as well. Since weaning age has an impact on patterns of infant mortality, health and disease patterning this was an important and interesting study.
One of the more interesting applications of trace element and stable isotope analysis (they are usually used in conjunction with each other) occured recently in Cape Town, South Africa. Back in the 1950’s a mass grave – dating to the 1800’s- of 31 individuals was excavated. The skeletons were then analyzed via stable isotope analysis. Science in Africa picks up the story from here:

In the 1950s, 31 skeletons were excavated from a shallow mass grave on the Cape Town foreshore, in an area that was once almost on the beach (subsequent land reclamation means that it is now some distance away). The front teeth of a number of the skeletons had been chipped or filed into points or notches (see the picture alongside); a custom practiced in many parts of the world, but not in the Cape. Isotopic analysis showed that the individuals who had decorated teeth (and some who did not) ate childhood diets that included C4-based tropical foods, but there was evidence for considerable dietary diversity. This heterogeneity was confirmed by analysis of strontium isotopes, which showed that different individuals came from areas with different geologies.
Combining this information with a search of the historical records revealed that these skeletons are very likely the remains of people on board the Paquet Real, a Portuguese slaving brig on her way from Mozambique to Brazil with 171 slaves on board. Slaves bought in Mozambique were often from the Makua, Yao or Maravi groups, who practised dental decoration of the patterns noted in these skeletons. In 1818, the ship was commanded by Captain De Souza, who was in debt and was trying to make extra money by sailing late in the season. Most slave ships sailed between August and October, when the winds were favourable. Captain De Souza left Mozambique in early February, and due to bad weather, the journey to the Cape took 71 days. The entire journey to Brazil should have taken only about 60 days, so by the time the Paquet Real reached the Cape, she had run out of provisions, and been damaged by storms. The ship’s arrival posed a problem to the British authorities, then in command of the Cape. Britain had outlawed the slave trade in 1808, and her colonies were not allowed to render assistance to slavers. The ship and its occupants were, however, in considerable distress, so there were humanitarian reasons for wishing to help her. But supplies cost money, and Captain De Souza could not pay. While the authorities considered what to do – should they insist that Captain De Souza surrender his ship? If so, what should they do with the slaves? – a storm blew up, and the Paquet Real was blown off her moorings and wrecked. The crew and most of the slaves were rescued, but a number of bodies subsequently washed up on the beach. It was probably these unfortunates who were buried in the mass grave.

The importance of this approach is:

Colonial Cape Town was a slave-owning society from its founding until 1834, when slavery was officially abolished. In the town, and in the agricultural hinterland of the Cape Colony, slaves did much of the hard work involved in farming, building and many other activities. It seems that slaves at the Cape lived very closely with their owners; slaves responsible for domestic duties often slept in their “masters'” houses. Thus it has proved extremely difficult to identify an archaeology of slavery at the Cape; in distinction to the plantations of southern North America, where slaves lived in their own cabins, ate different food from their “owners”, and sometimes even made distinctive kinds of pottery.

Fascinating, simply fascinating!

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