NEW YORK – In a study focused on enslaved and free African Americans at an ironworks site in Maryland, an international team led by investigators at the Harvard, the Smithsonian Institution, and 23andMe has shown that it is possible to genetically link ancient individuals to thousands of their living relatives using data from research-consented individuals using direct-to-consumer genetic testing services.
"Our study combines for the first time two transformative developments in genomics in the last decade: ancient DNA technology, which makes it possible to efficiently sequence whole-genome data from human remains, and direct-to-consumer genetic databases that contain data from millions of people who have consented to participate in research," David Reich, a human evolutionary biology researcher affiliated with Harvard University, Harvard Medical School, and the Broad Institute, said in a statement.
As they reported in Science on Thursday, Reich and colleagues from 23andMe, the Smithsonian Institutions, and elsewhere used enrichment capture genome sequencing to profile some 1.2 million SNPs across the genome in DNA from temporal bone samples for 27 ancient individuals buried in an African American cemetery at the Catoctin Furnace site in Maryland from 1776 to 1850.
The ironworks site near Thurmont, Maryland was home to both free and enslaved African Americans during the late 18th and early 19th centuries, the investigators explained. In addition to performing mining, furnace work, and other jobs at the site, individuals lived and died there, as evidenced by the presence of an African American cemetery that was excavated and transferred to the Smithsonian during a highway project starting in the late 1970s.
"The Catoctin Furnace Historical Society, Inc. (CFHS), was initially founded to save the Catoctin Furnace village and its archaeological and architectural heritage from this highway construction," the authors noted. "In recent years, its mission has expanded to include restorative justice, highlighting the critical role that enslaved and free African Americans played in the furnace's history and in the growth of industrial wealth and power in the young United States."
By comparing the ancient sequences to genotyping data for nearly 9.3 million research-consented 23andMe participants, they were able to tease out the ancestry of African Americans at the Catoctin Furnace site, along with their relationships to one another and to modern-day individuals in the 23andMe collection.
From the available genetic data, the investigators were able to cluster the ancient individuals tested in Maryland into five family groups, for example, teasing out parent-child, sibling, and other family relationships between individuals buried at Catoctin Furnace. They also flagged informative mitochondrial haplogroups, Y chromosome haplogroups, genetic risk factors for conditions such as sickle cell disease, and identity-by-descent sequences shared with 23andMe participants.
The team's analyses suggested the ancient individuals tended to have ancestry originating from Wolof and Mandinka groups in West and Central Africa, although some also carried paternal ancestry from Britain, Ireland, or other parts of Europe.
Nearly 41,800 individuals in the research-consented dataset from 23andMe were related to at least one of the ancient individuals profiled at Catoctin Furnace, the team reported, including distant relatives that appeared to have shared ancestry going back to Africa or Europe before the transatlantic slave trade. But a subset of 2,975 individuals had closer relationships to the Catoctin Furnace individuals, particularly 23andMe participants living in Maryland.
Such findings are particularly pertinent to modern-day family members of enslaved individuals who were not included in early US Census or historical records, the researchers explained.
"Even if we don't — and will never — know their names, this study allowed us to make connections between individuals who died more than 200 years ago and their living descendants," coauthor Henry Louis Gates Jr., director of Harvard University's Hutchins Center for African and African American Research, said in a statement.
"Recovering African American individuals' direct genetic connections to ancestors heretofore buried in the slave past is a giant leap forward both scientifically and genealogically," Gates added, "opening new possibilities for those passionate about the search for their own family roots."
Data from the current study is being made publicly available for analyses by other investigators. More broadly, the researchers explained, genetic testing, analysis, and interpretation strategies similar to those used in the Science study are expected to inform a range of future research efforts.
"The methodological approach we present in this study can be applied to the remains of deceased humans from other sites and contexts, offering a new scientific tool for individuals and descendant communities seeking greater knowledge of their ancestors, as well as archaeologists, bioarchaeologists, historians, and genealogists," the authors suggested.
In a perspectives paper appearing in the American Journal of Human Genetics on Thursday, members of the same team delved into the potential opportunities and ethical concerns raised by tapping into modern-day genetic databases to analyze and better understand genetic profiles in ancient individuals.
"We believe that joint analysis of historical genomes and data in genetic databases controlled by for-profit genetic ancestry companies represents an exciting new direction for aDNA research," the authors explained. "As aDNA research continues to leverage the power of ever-growing datasets, all parties involved in this work must make a concerted effort to predict ethical issues that may arise and proactively design an ethically sound strategy to ensure that sensitive genetic data remains protected."
In that article, the team set ethical guidelines for similar studies in the future, emphasizing the importance of consulting with affected communities and developing adequate consent processes for returning results to descendants or more distant relatives of ancient individuals.
"Future work will certainly add to and amend the guidance we provide, which is part of moving forward the ethics of the rapidly growing field of aDNA research," the authors wrote.
In the case of the Catoctin Furnace site, Gates explained, the current genetic analyses reflected calls from local African American community members who were engaged in the work and sought information on individuals in the African American cemetery.
"This study is an example of deploying scientific tools to address questions of long-standing interest to African Americans, at the community's request," he suggested. "It is a tool for empowerment of African Americans, rather than exploitation of a vulnerable population. I think it is a model of engagement to be emulated."
In a perspectives article in Science, Howard University and QuadGrid Data Lab biologist and anthropologist Fatimah Jackson called the Catoctin Furnace genetic study "pioneering" for its focus on local and broader community engagement rather than the use of researcher-initiated, "top-down" research.
"Investigating the issues of greatest importance to the African American community will be essential as research continues to examine the biological histories of this population," Jackson wrote. "Steps toward increasing African American participation in clinical trials, pharmacogenomic trials, and future ancestral genetic studies include training more African American researchers in the scientific methods used and ensuring that African American individuals are contributing to all aspects of such projects."