A first-of-its-kind DNA analysis has connected 27 free and enslaved African Americans buried in a Maryland cemetery to their 42,000 living relatives. The new research opens up a “historical gateway,” for Black Americans whose ancestors were stolen during the transatlantic slave trade, their family histories lost over the centuries of enslavement, reports Scott Maucione for NPR. The team published their findings Friday in the journal Science.

“This study demonstrates the power of genomics to reconstruct some of what has been destroyed,” Kari Bruwelheide, an anthropologist at the Smithsonian’s National Museum of Natural History, tells Reuters’ Will Dunham. “For African American and United States history, revealing these stories and family legacies is important to understanding and acknowledging who we are, where we came from and how we are connected to each other today.” 

The graveyard is located on an iron forge known as Catoctin Furnace, which began operating in the 1770s. For the rest of the 18th and early 19th centuries, mostly enslaved African Americans labored there, crafting items like stoves, pots and cannonballs in conditions that led to spinal injuries or inhaling furnace fumes. Many individuals were taken directly from Africa and brought to the forge because of their valuable iron working skills, per the Catoctin Furnace Historical Society.

Around 100 people who had worked at Catoctin Furnace and the surrounding community between the 1770s and 1840s,were buried there in unmarked graves. After that point, European immigrants dominated the workforce at the forge, and for more than a century, these European workers received credit for creating the high-quality wares that had been crafted by enslaved African Americans. 

The graveyard lay forgotten until 1979, when construction of a state highway uncovered human remains and artifacts. Archaeologists excavated 35 graves and turned the remains over to the Smithsonian Institution. In 2015, the president of the Catoctin Furnace Historical Society, Elizabeth Comer, contacted Bruwelheide and anthropologist Douglas Owlsey, also at the Smithsonian’s National Museum of Natural History, and requested they analyze the remains from Catoctin Furnace using new techniques. This approach was meant to provide a “more accurate and inclusive historical interpretation,” per a statement from the museum. 

Along with the historical society, the Smithsonian researchers partnered with scientists at Harvard University and Boston University, as well as with geneticists at the DNA-testing company 23andMe, to produce genome-wide data for 27 individuals buried in the cemetery and compare them to about 9.3 million voluntary research participants genotyped by 23andMe. 

Previously, genetic information from early African Americans was gleaned through mitochondrial DNA passed down by mothers, Y-chromosome DNA in men and from comparing DNA sequences in public databases, which often lacked Black participants, per a Harvard statement.

The researchers sequenced each historical individual’s entire genome, which uncovered five genetic families. Then, they developed an algorithm to compare historical DNA to that of living people. 

They identified 41,799 Americans in 23andMe’s database who are related to the buried individuals. Of them, 2,975 are close relatives who shared more and longer stretches of DNA with the people from Catoctin Furnace. The highest concentration of those close relatives were still located in Maryland today.

The new analysis also revealed that some of the individuals descended from the Wolof and Mandinka populations of West Africa and the Kongo people of Central Africa, per the Harvard statement.

So far, the researchers have not notified the participants of their connection to the buried people. “We are considering a way to thoughtfully and ethically return results to those in the 23andMe database who would like to know if they are connected to the Catoctin Furnace individuals,” Andy Kill, a 23andMe spokesperson, tells Reuters.

In the future, experts say this kind of research could contribute to uncovering more knowledge about Black Americans’ heritage, with their consent.

“For marginalized communities whose history has been obscured, this technology can be leveraged to tell their stories,” Jada Benn Torres, a biological anthropologist at Vanderbilt University who was not part of the new study, tells Science’s Andrew Curry. “There’s a beauty in connecting the past to the present.”

The Catoctin Furnace is just one of 111 Black cemeteries across the U.S. identified by the Black Cemetery Network. Alondra Nelson, a social scientist at the Institute for Advanced Study, tells the New York Times’ Carl Zimmer that similar studies could be carried out at other sites, provided that scientists continue to collaborate with local community members.

In a perspective piece published alongside the new research, Fatimah L. C. Jackson, a biologist and anthropologist at Howard University who was not involved in the study, writes that this community involvement is part of the value of the new analysis, per NPR. 

“What makes the work of Harney et al. so pioneering is that the research was initiated by an engaged local community of African Americans and results were structured to meet the needs, priorities and sensibilities of the larger African American community,” she writes. “This is the way that this type of research should be performed, and it provides a blueprint for future studies.”