A construction team working on a highway expansion in Maryland in 1979 discovered human remains in the yard of an 18th-century steelworks. Later, archaeologists discovered 35 graves in a cemetery where slaves were buried.
In the first effort of its kind, researchers today DNA from 27 African Americans buried in cemetery linked to nearly 42,000 living relatives. About 3,000 of them are so closely related that some people may be direct descendants.
Henry Louis Gates Jr., a historian at Harvard University and an author of the study, published Thursday in the journal Science, said the project marks the first time that historical DNA has been used to connect the enslaved African Americans among living people.
“The history of Black people is destined to be a dark, lightless cave,” said Dr. Gates. In new research, “you bring light to the cave.”
With a companion commentarywrites Fatimah Jackson, an anthropologist at Howard University, that the research is also significant because the local community in Maryland worked alongside geneticists and archaeologists.
“This is the way this kind of research should be done,” wrote Dr. Jackson.
The cemetery is located in a former ironworks called the Catoctin Furnace, which began operating in 1776. For its first five decades, enslaved African Americans did most of the work including cutting wood for charcoal and making items such as kitchen pans and shell casings used in the Revolutionary War.
Elizabeth Comer, an archaeologist and the president of the Catoctin Furnace Historical Society, said some of the workers were likely skilled at making iron before they were forced into slavery.
“When you steal these people from their village in Africa and bring them to the United States, you’re bringing people with a background in steel technology,” he said.
Upon their discovery, some of the remains were brought to the Smithsonian for curation. In 2015, the historical society and the African American Resources Cultural and Heritage Society in Frederick, Md., organized a closer look.
Smithsonian researchers documented the suffering suffered by the suffering in the furnace to the slave people. Some seeds have high levels of metals such as zinc, which workers inhale in furnace fumes. Teenagers injure their spines from hauling heavy loads.
The identities of buried African Americans are a mystery, so Ms. Comer looked to the diaries of local ministers for clues. He compiled a list of 271 people, almost all known only by one name. A family of freed African Americans, he discovered, supplied the furnace operators with charcoal.
From that list, Ms. Comer can trace a family of enslaved laborers to living people and a family of freed African Americans to another set of descendants.
At Harvard, researchers extracted DNA from samples of cemetery bones. Genetic similarity among 15 of the buried people revealed that they belonged to five families. A family consists of a mother lying next to her two sons.
Following Smithsonian guidelines, the researchers performed the genetic sequences public in June 2022. They then developed a method to reliably compare historical DNA with the genes of living people.
Éadaoin Harney, a former graduate student at Harvard, continued genetic research after he joined the DNA-testing company 23andMe, focusing on the DNA of 9.3 million customers who volunteered to participate in research efforts.
Dr. Harney and his colleagues looked for long stretches of DNA that contained identical variants found in the DNA of Catoctin Furnace individuals. These stretches reflect shared ancestry: Close relatives share longer stretches of genetic material, and more of them.
The researchers found 41,799 people in the 23andMe database with at least one stretch of DNA match. But most of those people were only distant cousins who shared common ancestry with enslaved people.
“That person may have lived several generations before the Catoctin individual, or hundreds or thousands of years,” said Dr. Harney.
The researchers also found that the people buried at Catoctin Furnace often carried ancestors from two groups: the Wolof, who now live in Senegal and Gambia in West Africa, and the Kongo, who now live 2,000 miles away. in Angola and Democratic Republic of Congo.
About a quarter of the individuals in the cemetery have only African ancestry. DNA from others usually shows traces of ancestry from Britain – the legacy of white men who raped Black women, as the authors noted in their study.
Most living people with links to the furnace live in the United States. Nearly 3,000 people have a particularly long stretch of matching DNA, which could mean they are direct descendants or can trace their ancestry to cousins of Catoctin Furnace workers.
A strong concentration of these close relatives is in Maryland, Dr. Gates. That continuity contrasts with the Great Migration, which brought millions of African Americans from the South in the early 20th century.
“The thing about Maryland is that it’s a border state,” said Dr. Gates. “That means a lot of people don’t leave, which is pretty interesting.”
Prior to the publication of their paper, the researchers shared the results with two families identified by Ms. Comer through his own research, as well as the African American Resources Cultural and Heritage Society.
Andy Kill, a spokesman for 23andMe, said the company is willing to share genetic results with relatives who participated in the new study. So far, the company has not been questioned.
But 23andMe has no plans to notify thousands of other customers with connections to Catoctin Furnace’s enslaved people. When customers agree to have their DNA used for research, their identifying data is removed to protect their privacy.
“We still have work to do in thinking about the best way to do that, but it’s something we want to do at some point,” Mr. Kill.
Jada Benn Torres, a genetic anthropologist at Vanderbilt University who was not involved in the research, said rushing to results is a mistake.
“This slow process gives us time to think about what the impact might be,” he said, “in terms of opening these boxes and looking and finding answers that we don’t know. that we have questions about.”
Catoctin Furnace is just one of many African American burial grounds scattered across the country. Alondra Nelson, a social scientist at the Institute for Advanced Study in Princeton, NJ, said similar studies could be conducted on the remains found in them, as long as scientists work with people taking care of cemeteries.
“If these types of projects are to continue, it will require researchers to have real interactions with these resilient communities,” said Dr. Nelson.