Genetic analyses could help reconstruct the origins of enslaved Africans, whom were shipped from ports like this one, in Ghana, to Europe, the Caribbean, and the Americas.

Genetic analyses could help reconstruct the origins of enslaved Africans, whom were shipped from ports like this one, in Ghana, to Europe, the Caribbean, and the Americas.

Courtesy of the John Carter Brown Library at Brown University

DNA reveals history of buried slaves

Construction projects unearth skeletons fairly often, but archaeologists knew right away that the “Zoutsteeg Three” were special. Named after the area of Philipsburg, the capital of the Dutch half of the Caribbean island of Saint Martin where they were found, the two men and one woman were accidentally dug up in 2010, along with artifacts dating to the 17th century. But they apparently hadn’t been born on Saint Martin: Their teeth had been intentionally chipped and filed into points and other shapes—a cultural practice foreign to the Caribbean but common in sub-Saharan Africa at the time. The find suggested that the trio had been born in Africa and brought to Saint Martin as slaves.

Now, thanks to a tricky genetic analysis, researchers have managed to trace the origins of the Zoutsteeg Three to at least two distinct linguistic groups in West Africa. The study paints a fuller picture of the African populations that were subjected to the transatlantic slave trade and suggests that DNA may help scientists reconstruct the life histories and ancestry of enslaved individuals.

Hannes Schroeder, an ancient DNA researcher at the University of Copenhagen, had previously studied the Zoutsteeg Three’s skeletons, determining that all three of them were between 25 and 40 when they died. Their dental modifications, along with the chemical isotopes found in their teeth, strongly suggested that they had been born somewhere in Africa, and radiocarbon dating placed their burial between 1660 and 1688. If he wanted to learn more about their origins, Schroeder knew he needed their DNA, but he wasn’t particularly optimistic about being able to sequence it. “The Caribbean is the last place you want to look for [ancient] DNA because it’s hot and humid,” and the genetic information that remained in the Zoutsteeg Three’s skeletons was indeed quite degraded, he says. The team used RNA probes to fish out the surviving bits of ancient human DNA from samples taken from their tooth roots and managed to collect enough nuclear and mitochondrial DNA to compare the genomes of the Zoutsteeg Three with those of 11 modern West African populations.

One of the men likely belonged to a Bantu-speaking group, possibly in northern Cameroon, while the other man and the woman were more likely non-Bantu speakers, maybe from Nigeria or Ghana, the researchers report online today in the Proceedings of the National Academy of Sciences.

“The idea that you can trace recent historical events by integrating ancient genomics and modern genomics is really exciting,” says Sarah Tishkoff, a geneticist at the University of Pennsylvania who compiled the reference database of modern African genomes that Schroeder’s team used. “It sets the stage for what can be done in the future.”

In the present, however, Schroeder is the first to admit that even his team’s fairly vague conclusions are plagued by uncertainty and that the three skeletons can’t be confidently placed into any particular population. From samples that contained only 0.3% to 7% human DNA, the researchers were able to reconstruct a rough picture of about 50% of the best preserved individual's genome. What’s more, even the modern samples came from only 11 African populations, out of the estimated 50 or so from which slaves were taken, Tishkoff explains. It’s possible that the genomes of the Zoutsteeg Three’s closest modern relatives simply haven’t been analyzed yet, but it’s also possible the populations they belonged to no longer exist. “At this point in time, we simply cannot trace any of these samples to a particular tribe or ethnic group in Africa,” Tishkoff emphasizes.

Still, the genetic differences between the Bantu and non-Bantu speaking groups are large enough that both Schroeder and Tishkoff expect that distinction to hold up. And even this broad ancestral difference underlines something important about enslaved Africans, according to Schroeder: They lived alongside other Africans who spoke different languages and came from different cultural groups. Analyzing the genomes of more enslaved Africans “and [finding] out where they came from … can tell us more about these people’s identities and how they transformed over the centuries that followed,” he says.

Schroeder’s lab is now collaborating with Howard University in Washington, D.C., to analyze the genetic ancestry of a small number of the enslaved and free Africans who were interred at the New York African Burial Ground in lower Manhattan between the 1690s and 1794. The site is now a national park, and discovery of the cemetery in the early 1990s—also during a construction project—ignited controversy about how to best excavate and study the remains. “The ethical issues are profound in dealing with skeletal materials of previously enslaved individuals,” says Fatimah Jackson, a biologist and anthropologist at Howard who previously worked as the director of genetics for the New York African Burial Ground Project. But in both the New York and Caribbean cases, “it seems to me that, as a scientist, the best way to ‘honor’ these unfortunate individuals is to allow their story to be told,” she says. “The story of a few can illuminate the condition of the masses.”

*Correction, 11 March, 11:25 a.m.: This article misstated the percentage of the best preserved individual's genome the researchers were able to reconstruct. It was about 50%, not 7%.