On Thursday, June 19th, Science Magazine shared the results of a groundbreaking study first published in the summer of 2023, titled "The Genetic Legacy of African Americans from Catoctin Furnace."
This study revealed the findings of a genetic analysis of historical individuals and demonstrated the value of combining DNA from these individuals with massive datasets generated through direct-to-consumer ancestry testing.
The research serves as a model for gaining direct insights into the genome-wide genetic ancestry of enslaved people in the historical United States.
According to Science Magazine, during the late 18th and early 19th centuries, Catoctin Furnace in Maryland relied heavily on a workforce of enslaved individuals to operate the iron furnace and perform various domestic and agricultural tasks.
Despite the significant role that Catoctin Furnace played in early U.S. history, including supplying munitions during the Revolutionary War, little is known about the African Americans who worked there or their descendants, especially when compared to the furnace's later, predominantly white workforce.
Science Magazine explains that Catoctin Furnace operated using both free and enslaved African American labor.
The research team, led by Harney et al., analyzed DNA from 27 individuals excavated from an African American cemetery that was uncovered 40 years ago during highway construction.
The authors found genetic evidence of biological family groups, identified modern African populations with whom these individuals may have shared ancestry, and even discovered possible distant relatives in the United States through identity-by-descent comparisons with consenting 23andMe customers.
This study illustrates that responsibly studied, long-buried DNA can help uncover hidden or forgotten histories of marginalized individuals.
The researchers produced genome-wide data for the 27 individuals buried in the Catoctin Furnace African American Cemetery.
They compared this data to that of approximately 9.3 million consenting research participants genotyped by 23andMe, Inc., addressing several key questions:
(i) How were the Catoctin individuals related to each other?
(ii) What were the origins of their African and European ancestry?
(iii) Where do their genetic relatives live today in the U.S., including their direct descendants?
(iv) What health insights can be gleaned from their genomes?
The researchers identified five genetic families among the Catoctin individuals, including biological mothers, children, and siblings, with most family members buried close to one another.
All but one of the Catoctin individuals had primarily African ancestry, with varying amounts of European ancestry.
To further understand their ancestry, the researchers developed a method to detect identical-by-descent segments of the genome shared between the Catoctin individuals and 23andMe research participants.
Two or more individuals share these segments of DNA because they inherited them from a recent common ancestor.
The researchers identified 41,799 close and distant relatives of the Catoctin individuals among 23andMe research participants.
Within Africa, they observed the highest rates of genetic sharing between Catoctin individuals and research participants who self-identified as belonging to the Wolof or Kongo ethnolinguistic groups.
In Europe, the highest rates of genetic sharing were found with research participants who have ties to Great Britain and Ireland.
In the U.S., participants from the South showed elevated rates of sharing, primarily reflecting distant connections to 23andMe research participants with sub-Saharan African ancestry, possibly tracing back to common ancestors in Africa.
When the researchers focused on genetic relatives who shared the most DNA with the Catoctin individuals, they found the highest rates of sharing in Maryland, suggesting that at least some descendants remained in the region after the furnace transitioned away from enslaved and paid African American labor.
Additionally, the study revealed that some of the Catoctin individuals carried risk factors for sickle cell anemia and glucose-6-phosphate dehydrogenase deficiency, genetic conditions that are common among African Americans today.