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‘Ancient DNA’ tools and 23andMe database uncover African American ancestries of thousands

This post originally appeared on StatNews.

New research that combines technology to sequence “ancient DNA” with direct-to-consumer genetic testing has identified tens of thousands people alive today who are genetically linked to enslaved and free African Americans who worked at a once-thriving Maryland iron forge in the late 18th and early 19th century.

The findings, reported Thursday in Science, are a step toward restoring difficult-to-obtain ancestry knowledge to African Americans who descended from enslaved people, whose life histories, or even names, were rarely recorded. Prior to 1870, the U.S. Census did not list enslaved African Americans by name, leading many of their lineages to fall off what some call “an information cliff.”


“These people lived and died and no one wrote a word about them,” said Doug Owsley, a biological anthropologist at the Smithsonian Institution who was part of the research team. “They are part of the American story, but you won’t find it in any history book.”

People eager for that ancestral information — including about 3,000 23andMe customers who researchers said may be closely related to the furnace workers — will have to wait, however. Officials of the genetic-testing company told STAT they were “considering a way to thoughtfully and ethically return results,” perhaps by finding a way to allow people to opt in to get the information, but they have no timeline for doing so.

The research is also helping to reveal the important role African American workers played at Catoctin Furnace — a factory that created a steady stream of pans used by Revolutionary War soldiers, potbellied stoves, and many of the bombshells and cannonballs instrumental to winning the decisive Battle of Yorktown.


For more than a century, credit for forging those high-quality wares went to European immigrants, who took over as hired labor only after slavery ended. “The narrative had been it was all European American workers because that’s who was still in the village,” said Elizabeth Comer, a historian and anthropologist who is president of the Catoctin Furnace Historical Society.

The paper also describes the ancestry, family relationships, and health conditions of one group of enslaved workers.

The research involved a detailed analysis of genetic material from tiny bits of inner ear bone from the remains of 27 African American people who were removed to the Smithsonian from a cemetery of the Catoctin Furnace in the late 1970s during highway construction. (The remains of 32 humans were removed from 36 graves, but viable DNA was found in only 27.)

The work makes use of technology that can assemble nearly complete genomes from historical human remains — it’s also been used to sequence Neanderthal DNA — and the large database of genetic-testing company 23andMe, two things that were not available, or even imaginable, when the bodies were exhumed.

“In my career, I would never have thought this possible,” said Owsley, whose career spans four decades. “I was blown away when I could look at this cemetery and see who was who.”

Much of the previous work on identifying the ancestry of African Americans was more limited because it relied on the more sparse mitochondrial DNA passed down from females or Y chromosome DNA from males instead of entire genomes, and did not take advantage of comparing that older DNA to a large genetic database, the researchers said.

In the new research, David Reich, a Harvard University geneticist who has pioneered studying ancient human populations by analyzing genome-wide patterns of mutations, and a team from 23andMe sequenced sites across the genomes of the colonial African Americans and compared those to the 9 million living people in the company’s database who had consented to take part in research projects.

Using a technique developed by Reich and a former postdoctoral student, Éadaoin Harney, now a population geneticist at 23andMe, the team detected what are known as “identical-by-descent” DNA segments that are shared because they were inherited from a common ancestor. The more identical segments two people share, and the longer they are, the more closely two people are related, Harney said.

The team found nearly 42,000 people in the database were related to one or more of the people buried at the Catoctin Furnace cemetery. Of these, nearly 3,000 were deemed to be closer relatives from five to nine degrees of separation — equivalent to ranging from being a great-great-great-grandchild to a first cousin six times removed.

Many of these closer relatives are clustered in Maryland, meaning some former workers’ families did not move far from Catoctin Furnace, Harney said. Other closer relatives appeared in southern states and in Southern California. The highest rates of relatives — both closer and more distant — were found in the South, reflecting the fact that many people with African ancestry live there.

A map showing how families were grouped in burials at the cemetery at Catoctin Furnace in northern Maryland. Courtesy Robert Wanner/ Bruwelheide et al (2020)

The lack of accurate records has stymied many Black Americans in their search for their family roots, and diminished the role many enslaved and free African Americans played in the founding and building of the nation. It’s believed that the roughly 45 million African Americans currently living who have a legacy of enslavement in their families are descended from a population of less than 460,000 Africans who were forcibly brought to this country.

“As Frederick Douglass famously said, ‘Genealogical trees do not flourish among slaves,’” Henry Louis Gates Jr., a Harvard professor and host of the popular PBS genealogy show “Finding Your Roots,” told STAT. A co-author on the paper, he advises 23andMe on historical matters and has participated in DNA testing to determine his ancestry since 2000. “I’m probably the most DNA-tested Black man in America,” added Gates.

He said many Black Americans are eager for genealogical information because so much information has been erased from the historical record by a system of slavery that dehumanized people by taking away their names and separating families.

“You remember the huge response to Alex Haley’s ‘Roots’?” he asked, referring to the best-selling novel and popular miniseries that ran in 1977. “It’s all about connecting to your family tree,” he said. “By doing this, we are defying one of the most heinous features of slavery, which is to deny living descendants of enslaved people knowledge of their ancestors.”

While he is not part of the decision-making process at 23andMe, Gates said, “I would hope they would say if you want to find out, here’s a channel you can click on.” From informing people about their family matters on his show, including adultery, he said he understands conveying ancestral information can be fraught. “There are white people descended from these people too,” he said. “They don’t want to give them a heart attack.”

Gates said when faced with conveying any unexpected genetic information, he always asked people if they wanted to be informed. Not a single person has said no, he said.

Joanna Mountain, who recently retired as a senior director of research at 23andMe and was a study co-author, defended 23andMe’s caution in releasing information to potential relatives. “Some people may not be ready to understand that they have connections to this story,” she said.

The awkwardness of 23andMe’s position is clear in a companion paper being published in the American Journal of Human Genetics, in which some of the same researchers wrote about the ethics of conducting the project. The “return of results to community stakeholders and research participants,” they wrote, is critical.

The company My True Ancestry — which advertises that it offers people the chance to see if they might be related to Viking maidens, Beethoven, and even Ӧtzi the Iceman — is already alerting some of its customers that they may be related to the African American workers at Catoctin Furnace. Even though the research being published Thursday was conducted in part by 23andMe scientists, federal guidelines required the government-funded scientists on the team to publicly release the genetic data.

They did so in June 2022 and My True Ancestry was able to compare the released historical genetic sequences to the 1 million people in its database. By directly looking for exact matches of DNA sequences called SNP chains in what the company calls “Deep Dive” matches, it found about 1,300 people in the company’s database who were closely matched genetically to five different Catoctin individuals, Markus Kangas, My True Ancestry’s CEO, told STAT.

23andMe scientists said they could not speculate on the precision of another company’s analyses, particularly with methodology that was not public, but noted that their analysis was optimized to detect genetic relationships. They said amateur geneticists might be able to link living people to the Catoctin workers now that the genetic data was public but cautioned that the analyses are difficult.

About 200 people who learned of connections through My True Ancestry have already contacted the Catoctin Furnace Historical Society, said Comer, its president, and a few have even traveled some distance to visit the site, which sits 12 miles north of Frederick, Md., and just south of the Pennsylvania state border. “People’s desire to connect is so great, and so visceral,” she said.

Comer said she was concerned that My True Ancestry’s genetic analyses were not as precise, and that some people being notified were only very distant relations, perhaps through a long ago, common ancestor. She returns emails to these potential descendants saying “any results that claim to show that the Catoctin individuals who are your close or distant relatives must be carefully scrutinized.” She added that she felt strongly that anyone who felt a kinship to the furnace and its workers are welcome and that such a connection should not be overly “biologized.”

A family views forensic facial reconstructions of historical workers at the Catoctin Furnace Historical Society Museum of the Ironworker. Courtesy Visit Frederick

Many who worked on the new project are excited about what the work reveals about the people who once lived and worked at the furnace. The genetic analysis found that the 27 people come from five genetically distinct families, many of them with ancestry reaching back to what is today Senegal and Gambia in West Africa and Angola and the Democratic Republic of Congo in Central Africa.

Those findings align with the historical record that shows roughly half of enslaved African Americans were taken from these regions, Gates said. Such knowledge has been difficult to obtain from modern Black Americans because so much genetic mixing has occurred over generations. (Gates’ ancestry, for example, is 49% African and 49% European, he said.)

Eight of the 27 individuals had at least 10% European ancestry, which the researchers said was “almost certainly driven by the rape of enslaved women.” “It’s very obvious,” Mountain said. “You can’t hide from the DNA.”

Discoveries at Catoctin have been eye-opening historically, since so much research on American slavery has focused on agrarian work such as cotton production. The industrial work at Catoctin shows many enslaved African workers were highly skilled, and brought important production knowledge from Africa to the budding American nation. “In Africa, every village had ironmaking,” Comer said. “Wrap your head around that.”

The skilled work and knowledge of the African American workers, Comer said, served to enrich white Americans with wealth and power. Even from little Catoctin Furnace, a massive amount of wealth flowed to Maryland’s first governor and first lady Louisa Adams, Comer said. She has even traced the family of E.U. President Ursula von der Leyen to the furnace.

“Even now you have this legacy of wealth and power, yet the people who really deserve the credit are lost,” she said.

For more than a decade, Comer has been working to restore the legacy of those people — and to find their descendants. She began studying and excavating the Catoctin Furnace site when she was 4 years old. She is not a descendant, but started by helping her mother, also a historian and now deceased, who was part of a group interested in learning more about the site and preserving the tiny village that had grown around it. It was her mother, Elizabeth Yourtee Anderson, who first brought the role of African American workers to light, Comer said. As a co-author on the paper, Comer is credited as the driving force behind the research project. She initiated the genetics analysis in 2015.

Despite the fact that nearly 300 African Americans had worked at the furnace, they had almost no known descendants, something that had always bothered Comer. Until the new genetics work was done, she knew of just a handful of descendants, some that she had discovered herself through dogged research, including combing through state archives and historical records such as invoices created when enslaved people were sold.

“What I’m trying to do is right a wrong,” she said. “What I really want is for people to travel to Catoctin and walk through the village and say, ‘My ancestors built this.’”

One of the people who can say that is Crystal Emory, 68. Emory, who lives about a half-hour from the forge, was able to trace her ancestry to Robert Patterson, a free African American with ties to Catoctin who worked as a collier, producing the charcoal used to run furnaces, and who also owned a farm.

Light-skinned and blonde, Emory said it was surprising, to say the least, to learn she had an African American relative, but she has since grown fascinated and honored. “I’m very excited to be able to share my ancestor’s story,” she said.

Because of tensions over race and slavery, however, some of Emory’s research about her ancestors has been frustrating and painful. “I’ve had people shun me when I say, ‘I’m interested in the slave side of the family — the slaves you owned,’” she said.

Emory said she is thrilled by the new DNA work that may help her find other descendants she is related to and has already asked two people who may be her relatives, based on information she’s gotten through, to take 23andMe spit tests to see how closely they may be related. “I found a cousin yesterday,” she said.

She feels strongly that people who are determined to be a close match to the Catoctin workers should be able to obtain that information from 23andMe. “Let people know,” she said. “That’s why people have submitted their DNA. They’re not saying, only tell me who I’m related to if it’s royalty.”

The Catoctin cemetery, the new report says, had close family members buried near each other. These groups consisted of mothers, children, and siblings — males were interred separately under the Moravian church burial practices used in the area. Many of the dead were teenagers, which was unusual even for colonial times, when the very old and very young were most likely to die, which suggests the hard labor and conditions at the furnace took a wrenching toll.

One teenager had a herniated disk, likely from carrying heavy burdens; many children had rickets likely due to a lack of sunlight reaching them through the furnace’s belching smoke. One young woman was buried with her 10-month-old infant; an older man had a back bent so badly, it created a 90-degree angle.

Despite the hardship evident in the remains, the new genetic work shows how strong the will to survive, have children, and be united with family was among enslaved people, said Fatimah L.C. Jackson, a biological anthropologist at Howard University. “Accurate and comprehensive genomics has the capacity to liberate contemporary descendants and honor ancestors,” she wrote in a commentary that ran with the research article. (She also noted the irony of enslaved workers forging the cannonballs that helped colonial Americans defeat a British Empire that had promised to free them.)

Jackson commended the scientists for an approach that included consulting with a local group, the African American Resources Cultural and Heritage Society, that Comer connected them with, and for doing work with, rather than to, the Black community. She called the research a “blueprint for future studies.”

The work also included communicating about the research with the few known living descendants of historical individuals with ties to Catoctin Forge, including Emory, Robert Patterson’s great-great-great granddaughter.

The study has Emory thinking more about the people laid to rest at Catoctin’s cemetery. She thinks it’s likely that she’s closely related to some of them. She also hopes more people — who are related to those workers and to her — will be visiting in the future.

“It’s always been about saying their names,” she said. “If we can’t say their names, we can at least give them a family.”

This post originally appeared on StatNews.