DNA evidence from Thomas Jefferson’s hair reveals the truth about his relationship with Sally Hemings

Opening a Bible that once belonged to Thomas Jefferson, staff at the Smithsonian National Museum of American History in 2011 discovered a reddish-blond hair pressed between the pages. That hair, suspected to have belonged to Jefferson himself, launched a DNA investigation spanning more than a decade that's now providing a long-missing puzzle piece regarding Jefferson's relationship with Sally Hemings, an enslaved woman in his household.

After spending years reconstructing DNA fragments, scientists have revealed the most compelling evidence to date that Jefferson, a founding father of the United States, also fathered children with Hemings — a relationship that has been long rumored but never definitively proven. How that investigation unfolded is documented in the book " History by a Hair : Thomas Jefferson, Sally Hemings & Solving a 200-Year-Old Mystery," written by Richard Kurin, a distinguished scholar and ambassador-at-large at the Smithsonian, and published on September 22.

Kurin is also senior author of a paper describing the methods that connected the former US president to Hemings' descendants, which involved delving deep into the genetics of the Jefferson and Hemings family trees. The paper, published September 21 on the preprint platform bioRXiv , has not yet been peer-reviewed.

In addition to testing the hair found in the Bible, the researchers also collected genetic material from multiple confirmed samples of Jefferson's hair, held in the collection of the Smithsonian. They compared that with DNA from descendants of multiple lineages: Jefferson and his wife Martha, Jefferson's brother Randolph, and two of Hemings' sons, Eston and Madison. (Hemings had four children who lived to adulthood, but only Eston and Madison claimed Jefferson as their father).

Matches in the DNA suggest the chance that Thomas Jefferson fathered at least one of Sally Hemings' children was 99.96%.

Previously, a genetic study from 1998 led by the late Eugene Foster, a retired pathology professor at Tufts University and the University of Virginia, claimed to prove Jefferson's parentage of Hemings' children. That study found a rare haplotype — a combination of genes — in the Y chromosomes of males descended from Thomas Jefferson's uncle. That same haplotype existed in descendants of Hemings, too. However, many experts questioned Foster's claim for one very important reason, Kurin told CNN.

"He didn't have Thomas Jefferson's DNA," Kurin said. "He didn't have something to directly compare living descendants of the Jefferson family to Madison Hemings and Eston Hemings and others that might have been the descendants of Thomas Jefferson." Critics of that the 1998 study said Foster's evidence merely connected Hemings' descendants to a male in the Jefferson lineage, and not necessarily to the former president.

"I thought, if we can get Thomas Jefferson's DNA, we could use that as the source of comparison to various descendants, and really firmly solve the question," Kurin said.

Kurin and his team were initially disappointed to find that the Bible hair wasn't the smoking gun that they thought it would be. To check whether the hair was Jefferson's, they compared its DNA with that of a living woman who was a direct descendant of Thomas Jefferson's mother along the family's female lineage. They expected to find identical mitochondrial DNA, which is genetic material specifically inherited from the maternal side. But their hopes were dashed when the two samples didn't match.

Still, they were able to access other hair samples that records attributed to Thomas Jefferson. These hairs, including a lock clipped at his deathbed, were in a packet provided by the Thomas Jefferson Foundation at Monticello, and had not previously been available for analysis. The scientists reconstructed and compared historic genome sequences of Jefferson and Hemings with DNA collected from 16 living individuals, including multiple descendants of Eston and Madison Hemings. These analyses found matches across genomes that linked Hemings descendants to Thomas Jefferson.

"What made this study so powerful is that researchers weren't just comparing two genomes," said Éadaoin Harney, a senior population geneticist at the 23andMe Research Institute. "Instead, they collected DNA samples from multiple people from different branches of the family tree."

In genetic analysis, larger sample pools provide more robust conclusions, said Harney, who was not involved in the new research. "By studying the patterns of DNA sharing across all of these individuals, it became possible to disambiguate exactly how the descendants of Sally Hemings were related to Thomas Jefferson," she told CNN in an email.

While the new book and paper focus on genomic data of well-known historical figures, these methods are also broadly useful for illuminating the obscured history of enslaved people, which has been a focus of Harney's own research. In a 2023 study of enslaved and free African Americans from Maryland, Harney used DNA analysis combined with other biomolecular and archaeological techniques to uncover individuals' ancestry and places of origin. The data also suggested links to people who still live in Maryland.

"Historical records are full of gaps, particularly when it comes to documenting the lives of people who occupied less privileged places in society," she said. "This is particularly true for enslaved Africans and African Americans, who are often only described in historical records as property."

Genetic analyses, such as those used in the new Jefferson study, can help restore connections that were lost because of slavery, Harney added. "The same tools can be applied to study the many enslaved people whose lives were never well documented, and help reconnect them with their descendants."

Whispers about Jefferson's sexual relationship with Hemings — who was 30 years his junior and a half-sister to his wife — have endured for more than 200 years. Initial rumors were fueled by local innuendo and supported by records aligning Hemings' pregnancies with Jefferson's presence at his plantation home of Monticello in Virginia. An article published in 1902 in the Richmond Recorder stated that "there is not an individual in the neighbourhood of Charlottesville who does not believe the story," regarding Jefferson fathering children with Hemings.

Though the conclusions of Foster's 1998 study were not universally accepted, that genetic evidence was compelling enough for the Thomas Jefferson Foundation to issue a statement two years later acknowledging "the strong likelihood that Thomas Jefferson and Sally Hemings had a relationship over time that led to the birth of one, and perhaps all, of the known children of Sally Hemings."

Finally laying that uncertainty to rest was enough of a motivation to keep Kurin and the other researchers going for more than a decade, despite their initial disappointment that the hair found in the Bible did not belong to Thomas Jefferson, he said.

"We had hit a dead end, but scientists are always looking for alternatives," he said. "I think we were propelled still by scientific and historical curiosity."

While the question of Jefferson's ancestry in Hemings' descendants may finally have been answered, another remains: Whose hair was pressed in Jefferson's bible? The researchers had collected enough of its fragmentary genetic data to know that it belonged to a female member of the Jefferson family, but that was all the information the team could learn, Kurin said.

"It's like a partial fingerprint," he explained. "That is still a lingering mystery."

Mindy Weisberger is a science writer and media producer whose work has appeared in Live Science, Scientific American and How It Works magazine. She is the author of " Rise of the Zombie Bugs : The Surprising Science of Parasitic Mind-Control" (Hopkins Press).

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