Harvard-Affiliated Researchers Analyze Ancient DNA to Explore History of Swahili Coast

Researchers affiliated with Harvard Medical School and the Department of Human Evolutionary Biology found Asian and African DNA in ancient human remains on the Swahili Coast in a paper published last month.

The study, published in the journal Nature, used the DNA of 80 Swahili individuals from medieval and early modern times to corroborate theories that Swahili civilization predated Persian settlement.

The DNA analysis found Asian migrants from the Persian Gulf settled amongst the preexisting indigenous African inhabitants around 1000 A.D. The analysis paints these medieval coastal cities as more interconnected with the region and less colonized than previously thought.

The study also found that before 1500 A.D., most of the Swahili Southwest Asian ancestry was Persian, which was described in the Kilwa Chronicle — the oldest oral history of the region. After that year, the DNA shows an increase in Arabian ancestry, substantiating preexisting evidence of relationships between the Arabian Peninsula and Africa.

Esther Brielle, a postdoctoral fellow in Human Evolutionary Biology, said the work of researchers started with the sequencing of DNA material of bones from the Swahili coast.

“We can’t understand the movements of people without ancient DNA at this point,” Brielle said. “Genetics gives us insight into the ancestry in a way that anthropology or archaeology cannot.”

Stephanie Wynne-Jones, a professor of African Archaeology at the University of York and a leading co-author of this study, said a colonial lens was typically used to understand civilization on the Swahili Coast before the paper was published. In this view, Asian traders from the Persian Gulf were assumed to have settled in the region.

“There’s been this binary approach to thinking about Arab settlers versus African indigenous societies, and what this research has done is sort of throw a hand grenade into that and say, actually, it’s not that simple. It’s not a binary,” Wynne-Jones said.

Rice University Anthropology professor and co-author Jeffrey B. Fleisher said conducting research on ancient DNA is a “multi-decade process.”

The study’s archaeological excavations began in 2009 before completion in 2016, according to the researchers.

Though the project initially began with excavating and examining material culture, the crux of the paper focused on ancient DNA, which the authors were able to extract from exhumed human remains, according to Wynne-Jones.

Because the authors were handling ancient human remains, the researchers consulted and included descendants of those who were buried throughout the research process, Wynne-Jones said.

“They were lifted, analyzed and reburied in one day. So we never had human remains just lying around,” Wynne-Jones said. “At the end of the season, we also had a sort of blessing. And everyone came and we ate goat and the Imam said a blessing again over the graves.”

“We did all of this to bring the community with us with this study,” she added.

Brielle said ancient DNA allows researchers to “take drastic leaps” in understanding the past.

“If you have a Neanderthal or Denisovan skeleton, there’s only so much you can understand from that,” Brielle said. “There’s so much more that you could figure out from the ancient DNA. I hope that this field progresses as quickly as it is right now.”