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What can science tell us about slavery: using bone chemistry to identify slaves
at the Cape
Judith Sealy & Glenda Cox, Department of Archaeology,
University of Cape Town
 Slavery has existed in Africa for centuries: early written records mention
slaves, and the practice almost certainly pre-dates any surviving documents.
After the 15th century, as European nations started to establish empires, the
demand for slaves increased and a massive trade in people developed. Somewhere
between 10 million and 30 million Africans were deported from the continent,
mostly to the Americas and to the Near East. Large areas of Africa were
depopulated, economic development was severely depressed and the societies left
behind were fragmented and destabilized.
Historians and archaeologists have long been interested in trying to
understand more about the slave trade, and about slave-owning societies. One
problem is that the records that survive are almost always from the point of
view of the slave traders, or slave owners. Most slaves were illiterate, and
even if they could read and write, they were certainly not encouraged to
document their experiences. Thus the written history of slavery is inevitably
partial and one-sided. But history leaves its mark in more than just written
documents: the story of the past can also be coaxed out of the buildings where
slaves were housed, the tools they used in their everyday work, and the graves
in which they were buried.
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.
Early Cape Town was a cosmopolitan mix of settlers and slaves, free burghers,
convicts, political prisoners, 'free blacks', indigenous Khoisan people and
others. Life was hard, and deaths a frequent occurrence. The bodies of people
who had been Christians in life were buried in designated graveyards.
Non-Christians, including most slaves, were buried in informal burial grounds on
the edge of town. Construction work in central Cape Town today regularly exposes
historic human remains. Most do not have gravestones, or other means of
identifying the deceased. There is little to help us reconstruct who these
people might have been, other than the bones themselves. This is where the
chemistry comes in. Using stable isotopic analysis, in combination with unusual
features of bones and teeth, it has been possible to identify unambiguously the
physical remains of at least some first-generation slaves.
Bones and teeth embody - literally - information of many kinds. Habitual
behaviours in life leave characteristic signs on the bones: pipe-smokers who
clenched their pipes between their teeth often had unusual facets - even notches
- on their teeth. Sailors had very well-developed upper body musculature, and
the bones of their arms and torsos grew bigger and stronger to support these
muscles. But bones and teeth contain information also at the molecular level, in
their chemical composition. In the December 11, 2001 issue of Science in Africa,
Julia Lee-Thorp described how stable carbon isotope ratios (13C/12C) in fossil
bones help us to reconstruct the diets of our early hominid ancestors, several
million years ago. These techniques can help us investigate historic skeletons,
too.
Carbon occurs in nature in two stable forms, 12C and 13C. These two isotopes
react in exactly the same way in chemical reactions, but 12C (being smaller and
lighter) reacts slightly faster than 13C. When plants convert atmospheric CO2
into plant tissue by photosynthesis, they incorporate proportionally more 12C
and less 13C than in the carbon dioxide substrate: they discriminate against the
heavy isotope. Different photosynthetic pathways discriminate to different
degrees: so-called C3 photosynthesis, employed by trees, shrubs, and grasses in
temperate environments, discriminates against 13C very strongly. C4
photosynthesis, characteristic of tropical grasses, discriminates much less
strongly. Thus the bones of animals - and people - eating C3-based foods contain
very little 13C. This is the pattern seen in inhabitants of areas dominated by
C3 plants, including the region around Cape Town, and most of Western Europe. C3
foods include wheat, barley, oats, rice, and nearly all fruit and vegetables.
People from hot, summer-rainfall (i.e. tropical) areas, on the other hand,
usually rely on tropical crop plants such as millet, sorghum or maize. These are
C4 plants, and lead to higher concentrations of bone 13C (at least, compared
with C3 consumers).
Nitrogen isotopes can also be used in this way, as natural tracers. Nitrogen
is more complicated, but many successful case studies have used the proportions
of the stable isotopes 14N and 15N in bone to separate consumers of
terrestrially-based diets from seafood-rich diets (which generally lead to high
bone 15N).
So analysis of bone from a historic skeleton can tell us whether the remains
are those of a person who, in life, ate the kind of diet characteristic of
Western Europe (or the Cape), or whether s/he ate tropical crops and therefore
probably came from a tropical home. We can achieve more resolution by examining
multiple elements from a skeleton: teeth form in childhood, and record mostly
childhood diet, while bone continually remodels throughout life, capturing the
isotopic signal of later life.
 This approach provides an excellent avenue for investigating historic human
remains. The most intensive study of a single individual to date is of a female
skeleton from Vergelegen, the country estate of Willem Adriaan van der Stel,
Governor of the Cape from in the early 1700s. She was middle-aged when she died,
probably in her fifties, and suffered badly from arthritis in her hands, neck
and lower back. Isotopic analyses of her teeth indicate that as a child, she ate
a diet that included tropical grains, but no seafood. This continued until her
third molars (wisdom teeth) were fully formed, probably in her twenties. From
early adulthood, her diet changed dramatically: tropical grains became less
important, and seafood much more so. This almost certainly reflects her capture
and sale as a slave, eventually coming to live at the Cape. More than half of
the slaves brought to the Cape came from the African mainland, or from
Madagascar. This woman was probably African, enslaved as a young woman and
brought to the Cape, where she worked and eventually died on the Governor's
estate. She was buried beneath the floor of the slave lodge where she once
lived.
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.
Human remains regularly have to be disinterred from old burial grounds
scheduled for development. Work on the remains of slaves is helping to broaden
our understanding of their lives. Some were buried with grave goods: beads,
smoking pipes, razors or knives, and in one case, two valuable silver items that
were unlikely to have been the legal property of a poor person. Slaves were part
of a diverse underclass at the Cape; one that incorporated people from Africa,
the East and from Europe, as well as locals. This cosmopolitan mix was
incorporated into Cape society to form the working class of the colonial era.
References and Further Reading
Cox, G. & Sealy, J. (1997). Investigating identity and life histories:
isotopic analysis and historical documentation of slave skeletons found on the
Cape Town foreshore, South Africa. International Journal of Historical
Archaeology 1, 207-224.
Cox, G., Sealy, J., Schrire, C. & Morris, A. (2001). Stable carbon and
nitrogen isotopic analyses of the underclass at the colonial Cape of Good Hope
in the eighteenth and nineteenth centuries. World Archaeology, 33, 73-97.
Kelly, K.G. (1997). Slave trade in Africa. In Vogel, J.O. (ed.) Encyclopaedia
of Precolonial Africa: 532-535. Walnut Creek: Altamira Press.
Ross, R. (1983). Cape of Torments: slavery and resistance in South Africa.
London: Routledge & Kegan Paul.
Sealy, J.C., Morris, A.G., Armstrong, R., Markell, A. & Schrire, C.
(1993). An historic skeleton from the slave lodge at Vergelegen. South African
Archaeological Society Goodwin Series 7, 84-91.
Sealy, J., Armstrong, R. & Schrire, C. (1995). Beyond lifetime averages:
tracing life histories through isotopic analysis of different calcified tissues
from archaeological human skeletons. Antiquity 69, 290-300.
Shell, R.C.H. (1994). Children of Bondage: a social history of the slave
society at the Cape of Good Hope, 1652-1838. Hanover, NH: Wesleyan University
Press.
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