DNA analysis has linked 27 individuals buried in a Maryland cemetery for African Americans – most of them slaves – to nearly 42,000 living genetic relatives, according to a new report.

“This study demonstrates that when studied responsibly with input from stakeholders, long-buried DNA can be used to uncover obfuscated or forgotten histories of marginalized individuals,” states a summary of the research published Thursday (Aug. 3) in the journal Science.

Construction workers expanding a Maryland highway in 1979 were the first to discover the remains. The cemetery was located at a former ironworks facility named Catoctin Furnace that operated in the 18th and 19th centuries using the labor of free and enslaved African Americans.

Elizabeth Comer, an archaeologist and the president of the Catoctin Furnace Historical Society, told The New York Times that some of the laborers were likely skilled ironworkers before their enslavement.

“When you’re stealing these people from their village in Africa and bringing them to the United States, you were bringing people who had a background in iron technology,” said Comer, who is a co-author of the DNA study.

Comer’s investigation, separate from the DNA study, traced one family of enslaved workers found in the cemetery to living people and one family of freed African Americans to another set of descendants.

Meanwhile, researchers at Harvard University extracted DNA from the remains and found genetic similarities among 15 of the buried people that belong to five families, including a mother buried with her two sons, The Times reported. In 2022, the researchers made the genetic sequences public and developed a way to accurately compare historical DNA to living people.

23andMe, the DNA-testing company, compared the extracted genetic material to the DNA of 9.3 million customers who volunteered to participate in the research. The effort found 41,799 matches, most of which shared a common ancestor hundreds or even thousands of years ago.

But almost 3,000 23andMe customers had a much closer genetic link, suggesting that they could be direct descendants or cousins of the buried ironworkers.

Dr. Henry Louis Gates Jr., a Harvard University historian and a co-author of the study, told The Times that the close living relatives are concentrated in Maryland, in contrast with the Great Migration in which scores of Black Americans migrated from slave states to the North in the early 20th century.

“The thing about Maryland is that it’s a border state. What this means is that a lot of people didn’t leave, which is quite interesting,” he said.

The researchers also traced the African ancestry of the buried people to two ethnic groups: the Wolof, who live in modern-day Senegal and Gambia, and what had been the Kingdom of Kongo, with roots today in Angola and the Democratic Republic of Congo. About 75 percent of the individuals had traces of ancestry from Britain – the result of White men who raped Black women, the researchers said.