Genetic analysis of hair samples indicates a 99.96 percent chance that Thomas Jefferson fathered children with Sally Hemings. The research was detailed in a new book and a preprint paper released in late September.
The 99.96 Percent Probability Found in Jefferson's Hair
New research led by Richard Kurin, a distinguished scholar at the Smithsonian, has produced the most definitive evidence to date linking Thomas Jefferson to Sally Hemings. according to the report, the investigation spanned over a decade and culminated in a finding that there is a 99.96 percent probability that the third U.S. president fatered at least one of the children born to Hemings, an enslaved woman in his household.
The breakthrough began in 2011 when Smithsonian National Museum of American History staff discovered a reddish-blond hair pressed inside a Bible once owned by Thomas Jefferson. While that specific sample did not initially provide the expected match, the team eventually analyzed other hair samples provided by the Thomas Jefferson Foundation at Monticello, including a lock of hair clipped from the president at his deathbed.
Why Eugene Foster's 1998 Study Lacked the "Smoking Gun"
This new genomic data addresses a long-standing scientific debate that began with a 1998 study led by Eugene Foster of Tufts University and the University of Virginia. Foster's research identified a rare Y-chromosome haplotype shared by descendants of Thomas Jefferson's uncle and descendants of Sally Hemings, which suggested a familial link.
However, as Richard Kurin noted in the source report, the 1998 study was criticized because it lacked DNA from Thomas Jefferson himself. Critics argued that the shared genetic markers only proved a connection to the broader Jefferson male lineage, not necessarily to the former president. By utilizing direct samples from Thomas Jefferson, the Smithsonian team has effectively closed the gap that left the Foster study open to skepticism.
Linking 16 Living Descendants to the Monticello Packet
To ensure the results were robust, the research team reconstructed historic genome sequences and compared them against DNA from 16 living individuals. These participants included descendants of Madison and Eston Hemings, the two sons of Sally Hemings who claimed Thomas Jefferson as their father.
Eadaoin Harney, a senior population geneticist at the 23andMe Research Institute, observed that the power of this study lies in its sample size. By comparing DNA from multiple branches of the family tree—including the lineages of Thomas Jefferson's wife Martha and his brother Randolph—the researchers were able to disambiguate the specific relationship between the Hemings descendants and Thomas Jefferson.
Eadaoin Harney and the Recovery of Obscured Enslaved Histories
Beyond the specifics of the Jefferson case, this methodology represents a broader shift in how historians and scientists approach the legacy of slavery. Eadaoin Harney has utilized similar biomolecular and archaeological techniques in a 2023 study of enslaved and free African Americans in Maryland to uncover ancestral origins that were intentionally erased from official records.
Because enslaved people were historically documented as property rather than people, their family trees are often riddled with gaps. The use of genomic sequencing, as seen in the Thomas Jefferson investigation , allows researchers to restore familial connections that were severed by the institution of slavery, providing a scientific voice to those omitted from the written archive.
The bioRxiv Preprint and the Missing Peer Review
Despite the high probability of the findings, a critical piece of the scientific process remains outstanding. The study was published on September 21 on bioRxiv, a preprint platform, meaning the data has not yet undergone formal peer review by inependent scientists.
While the accompanying book, History by a Hair, presents these findings as a solution to a 200-year-old mystery, the lack of peer review means the scientific community has not yet officially vetted the methods or the conclusions. Until the paper moves from a preprint to a peer-reviewed journal, the 99.96 percent figure remains a strong claim rather than a scientific certainty.
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