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New DNA Techniques Help Scientists Find Origins of African Slaves

Thanks to advances in genetic technology, scientists are using DNA from long-buried human remains to trace the origins of African slaves brought to the New World.

In 1985, geneticist Svante Pääbo announced he had sequenced DNA from an Egyptian mummy, making the first-ever such claim relating to genetic material of an ancient human. But after Pääbo realized his results were likely the result of contamination by modern DNA—possibly his own—he and other geneticists turned increasingly to ancient human remains found in colder climes, as heat and humidity speeds up the decay of DNA. To take just one example, in 2012 biologists were able to map the entire genome of Otzi, the 5,000-year-old “Iceman” found frozen in the Alps. In fact, Otzi’s remains are so well preserved that scientists have even able to analyze the DNA of a common stomach bacteria found in his gut.

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As DNA technology advances, however, genetic researchers have been able to gain ground in warmer climates. Last fall, scientists published the first ancient genome from Africa, extracted from a 4,500-year-old skeleton in Ethiopia. At the same time, another team of researchers trained their efforts on using DNA from African slaves found buried in the Caribbean and elsewhere to trace their origins back to Africa.

In 2010, archaeologists excavated the site of a 17th-century cemetery on the Caribbean island of St. Martin, in an area that was colonized by the Netherlands. In the skulls of two men and a woman, who were between 25 and 40 when they died in the late 1600s, the scientists found filed teeth. Tooth filing was a common practice in sub-Saharan Africa, suggesting that these individuals were slaves brought to work on the island’s sugar plantations. Just five years ago, it would have been unrealistic to think that 400-year-old human remains buried in the hot, humid Caribbean climate would yield significant information. But a new procedure, known as whole-genome capture, is making it possible for researchers to sequence even degraded genetic material. Developed at Stanford University, the technique concentrates degraded genes so scientists can obtain enough material to sequence.

As reported in a recent issue of the journal Proceedings of the National Academy of Sciences of the United States of America, the biological anthropologist Hannes Schroeder of the University of Copenhagen and his colleagues compared the DNA they analyzed from the individuals found in the St. Martin cemetery with a database of material from modern-day Africans. They found that all three came from different parts of Africa: One of the men probably came from what is today northern Cameroon, while the other man and the woman may have come from Ghana or Nigeria. As the DNA database for modern Africans is currently far more limited than the one that exists for Europeans, the scientists were unable to narrow down the origins more specifically. They did conclude that the three Africans might have traveled on the same slave ship, and that they represented a mix of ethnicities and spoke different languages.

A map showing the sources of slave supply and routes of distribution.  (Credit: Hulton Archive/Getty Images)

A map showing the sources of slave supply and routes of distribution. (Credit: Hulton Archive/Getty Images)

Schroeder and his team are also investigating human remains found at St. Helena, a British colony in the southern Atlantic Ocean, off the coast of Africa. (The island is most famous as the place where Napoleon died in exile in 1821 after his crushing defeat at the Battle of Waterloo.) In the 19th century, British Royal Navy ships patrolled the African coast in order to intercept slavers, and between 1840 and 1872, they took more than 26,000 slaves found aboard the ships to St. Helena. Some 5,000 to 8,000 of the newly freed slaves died during the course of their ordeal, and were buried on the island. Recently, workers building a new airport found some 128 graves, containing the remains of 325 individuals. The researchers have been able to extract DNA from 20 people (17 males and three females) and found that all but two of them were Bantu speakers who probably originated from West Central Africa, but that not all came from the same groups.

A third focus of the researchers’ work is El Chorro de Maita, a cemetery in southeastern Cuba dating to the early 16th century. Archaeologists found 133 people in 108 graves on the site, which is named for a nearby spring. It is the only cemetery in Cuba that is known to contain the remains of native Taino people, while isotope analysis has also revealed the presence of individuals from West Africa and Mesoamerica. The latter remains, which may come from Maya populations on the Yucatan peninsula, provide further evidence of a European-directed slave trade involving natives of Mesoamerica as well as Africa.

Though Schroeder’s team has tried to extract DNA from 10 samples taken from the Cuban cemetery, it has not had much success tracking their origins so far. In the end, as in the case of St. Martin and St. Helena, more information is necessary, specifically more genetic sampling. With luck, advancing DNA technology will ultimately provide such data, enabling scientists to more fully unlock the mysteries surrounding the origins of the New World’s enslaved peoples. As Schroeder told National Geographic: “In the not too distant future, we hope we can say more.”

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