Tracking Hunter-Gatherers - Archaeology Magazine Archive

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Tracking Hunter-Gatherers October 27, 2006

Bone chemistry and a multidisciplinary approach reveal evidence of unexpected lifestyle diversity in prehistoric South Africa.

(Courtesy Judith Sealy)

Every subdivision of anthropology--biological, cultural, and archaeological--can contribute to the overall understanding of ancient societies. Judith Sealy, an archaeologist at the University of Cape Town, studies South African hunter-gatherers who lived 4,500 to 2,000 years ago. Her research, published in the August issue of Current Anthropology, demonstrates how all avenues of anthropology can work with each other. Sealy analyzed the bone chemistry of skeletons excavated from archaeological sites, which led to a surprising revelation. Populations in two geographically close locations had consumed different diets, a pattern that goes against what is known from studies of modern hunter-gatherer societies in South African. ARCHAEOLOGY asked Sealy to explain her findings, and comment on the increasingly integrated nature of anthropological research.

Why did you decide to focus your research on the chemistry of archaeology?
In my undergraduate degree I majored in both chemistry and archaeology, partly as insurance against the limited job prospects in archaeology. It also meant, however, that I was well equipped to do graduate work in archaeometry--with Nick van der Merwe, who was at that time professor of archaeology here in Cape Town, and was pioneering the field of stable isotope research in archaeology. This offered a fresh and exciting way to address otherwise intractable problems in archaeology.

Can you explain what an isotope is and how it can be useful to the study of ancient populations?
Isotopes are different forms of the same chemical element with different numbers of neutrons in their nuclei, leading to different atomic weights. For example, the most common isotope of nitrogen is nitrogen 14, with seven protons and seven neutrons in its nucleus. About 0.4% of nitrogen atoms have an extra neutron, giving an atomic weight of 15. While the two forms undergo exactly the same chemical reactions, less energy is required to make and break chemical bonds with the lighter 14N, so it tends to be favored over 15N. Therefore, as plants fix nitrogen from atmospheric N2, or animals and humans digest their food and use its nitrogen to build protein-rich body tissues, the end products have measurably different ratios of 15N/14N compared with the starting materials. Along the southern coast of Africa, as in many other parts of the world, 15N/14N ratios in land plants and animals are lower than those in marine animals. These ratios are incorporated into consumers, including people--with some additional "sorting" of 15N from 14N at every step in the food chain. This means that if we measure 15N/14N ratios in the bones of people who lived along this coastline thousands of years ago, we can tell the relative importance of terrestrial and marine foods in their diets.

Through chemical analysis of bone collagen from 69 skeletons dated from 4,500 to 2,000 years before present, what foods were you able to determine that Holocene populations in Robberg/Plettenberg and the Matjes River Rock Shelter were consuming?
In this area, people were able to choose from a long menu of foods including venison and the meat of other wild animals, berries, edible roots and corms, particularly of plants in the iris family, seafood including shellfish, fish, seabirds, stranded dolphins or whales, and much else. All these items have been identified in excavated food remains. It is, however, harder to know their relative importance. Neither conventional archaeological techniques nor isotope analysis (for different reasons) permit precise quantification of individual foods, but it is clear from the high ratios of 15N/14N in their bones that people buried at Robberg/ Plettenberg Bay ate unusually large quantities of high trophic level [animals high on the food chain] marine foods, very likely the meat of seals and large predatory fish caught in the deep waters surrounding the Robberg Peninsula. Bone tissue accumulates over many years, so this was a long-term dietary pattern. People buried at Matjes River Rock Shelter, on the other hand, ate much more mixed diets, with more terrestrial food or low trophic level [low on the food chain] marine foods, such as shellfish.

Why do you think their diets were different? Why is this finding important or surprising?
Today, there is a seal colony on the Robberg Peninsula, and it was probably there in the past as well. (This inference is based on the age distribution of seals that ancient people butchered and ate.) Mainland seal colonies are relatively rare (most colonies are on offshore islands, which offer protection from predators), so this would have been a special opportunity for hunter-gatherers--a type of living larder. In addition, the peninsula juts out into deep water, allowing access to fish not usually caught by shore-based anglers. People who lived at Robberg/Plettenberg Bay made the most of their good fortune, while people who lived at Matjes River Rock Shelter didn't have these advantages. What's surprising about it is the degree of specialisation in local resources, from which we can infer that these people were living within relatively small areas, rather than trekking regularly across large areas of landscape. This is unexpected, given the very mobile lifestyle of most recent southern African hunter-gatherers.

How does ethnographic research contribute to the analysis of Stone Age societies in South Africa?
Later Stone Age societies were the ancestors of communities who continued to live a foraging lifestyle, in the Kalahari and elsewhere, into the nineteenth and twentieth centuries. Studies of Kalahari foragers have been of enormous importance in anthropology in recent decades. In some respects, there are clear similarities between recent and ancient southern African hunter-gatherers, and the ethnographies have provided valuable insights into earlier societies. For example, aspects of belief systems recorded in the Kalahari in the twentieth century are also expressed in rock paintings that may be several thousand years old.

Why is it sometimes misleading?
There is an extensive literature on the use of ethnography in archaeology and the dangers of simplistic assumptions that past societies were necessarily like recent ones. It is, however, almost always the case that the historical-anthropological evidence is far richer and more detailed than the archaeology, so when archaeologists identify, among the remains they have excavated, some component of a better-known recent system, it is very tempting to infer broader similarities. It is often very hard to recognize when similar elements were deployed in different social and cultural systems in the past, as I argue is the case here.

How does the contemporaneous stone tool technology add to our understanding of these populations?
The excavated artifactual assemblages from both Nelson Bay Cave and Matjes River show broadly similar patterns of change through time, consistent with trends documented more widely in southern Africa. We now need to look closely to try to find out whether people used subtle differences in material culture to express the economic and social distance between groups that we can reconstruct from the isotope analyses. This is very much a focus of current research.

There were 120 burials at the Matjes River Rock Shelter, but other burials in the area are scattered and variably adorned. What can be inferred from this?
It is true that many burials were isolated interments in scattered localities, but other caves also contained large numbers of graves--Whitchers Cave, for example. Unfortunately, this was excavated early in the twentieth century, and most of the remains recovered have been lost. We are interested in what the placement of graves meant to the survivors, and how this fitted in with peoples' concepts of the landscape.

(Courtesy Judith Sealy)

What does the painted seal scapula found in the cave at Knysna tell us about the hunter-gatherer society that created it?
This is a unique artifact--it's the only painted bone we have from South Africa, so interpretation must be cautious. Paintings on the walls of caves and rock shelters, however, expressed aspects of people's belief systems, including ideas about relationships between animals and humans in this world and in the spirit world. The animals depicted are usually larger species charged with symbolic power. The choice of a seal scapula and the images painted on it, of which the left-hand one, at least, looks very seal-like, hints that seals may have been important in a spiritual, as well as an economic sense.

You describe the societies as succumbing to "opportunistic sedentism." What do you mean by this, and why is it significant? How might being sedentary affect other aspects of life?
The idea is that people might initially have practiced a degree of sedentism in areas where there were rich resources, because there was no need to move. Early on, this is likely to have been a flexible pattern. When population densities rose, and there were limited options for moving, settlement patterns became more fixed--increasing our chances of recognizing them in the archaeology. Cross-culturally, more settled lifestyles require people to develop new methods of dealing with conflict, they allow storage of food or other commodities, opening up the possibility of differential access to resources and thus to social inequality. Southern Cape peoples probably didn't go very far down this road, but these are interesting questions.

Your research is a great example of "bioarchaeology," the integration of archaeological data with biological evidence. How do you see archaeology, physical anthropology, and cultural anthropology fitting together?
I think that using multiple approaches can be valuable, at least for some kinds of research questions. They need to be the kinds of questions to which each sub-discipline can make a useful contribution, and they need to be framed in an appropriate way. I didn't set out to do this at the start of this project--I began with the much simpler goal of investigating dietary change over time, and the study grew outward from there.

How do you derive one coherent story from these different lines of evidence?
One hopes it turns out to be coherent! Contradictions identify issues that need further work, which can be helpful in itself. But I think it's got a lot to do, first, with the way one frames the question, and then tries to work the different avenues of investigation so that they eventually converge and one can construct a sensible picture.

Describe the implications of your research in regards to the ongoing story of early human societies in South Africa.
It seems that societies were organized in more ways than we have previously realized. I think it's important to try to understand the different dimensions of this variation--how they varied, when, where ... there's a great deal of basic description and documentation that still needs to be done, before one can tackle the question of why. There's been quite a bit of work on the archaeology of hunter-gatherers in southern Africa, but it's only a tiny drop in the bucket of what's needed--and soon, because many sites, especially along the coast, are being destroyed by development.

What future research do you have planned?
Lots! This is an ongoing project--I hope to be able to do more isotopic analyses, I'm working with several graduate students on artifact assemblages from old excavations and, we hope, new ones in the future. I'm also thinking about ways to explore some of these issues in older time periods.

© 2006 by the Archaeological Institute of America