New DNA analysis on Thomas Jefferson’s hair has provided strong evidence supporting the longstanding claim that the third U.S. president fathered children with Sally Hemings, a woman he enslaved. The findings, the result of a 15-year interdisciplinary effort involving archaeologists, genealogists, geneticists, and historians at the Smithsonian Institution, build on earlier research from the 1990s by adding more detailed genomic data and refined analytical methods.

Researchers sequenced Jefferson’s entire genome from a few strands of hair collected after his death and compared this genetic information with DNA samples from 13 individuals believed to be descendants of both Jefferson and Hemings. The results indicate that Jefferson himself, rather than another male relative from his family line, fathered at least two children with Hemings. Both Eston and Madison Hemings, two of Sally Hemings’s children who survived to adulthood and were eventually freed, were shown to have inherited significant portions of Jefferson’s DNA.

The relationship between Jefferson and Hemings, who was enslaved at his Monticello estate and is thought to have been the half-sister of Jefferson’s wife Martha, has been the subject of debate and speculation for more than two centuries. The new work provides a more nuanced understanding of the timeline and nature of their association, which likely began when Hemings was a teenager and Jefferson was in his mid-forties. The research sheds light on the complexities of slavery and Jefferson’s private life, contrasting notably with his public rhetoric on equality.

The findings are detailed in "History by a Hair," a book by Smithsonian scholar Richard Kurin, who led the project. Kurin emphasized how advances in genetic science are helping to illuminate historical questions previously considered unresolvable. The Smithsonian plans to exhibit key artifacts and share further details in coming months.

While the Thomas Jefferson Foundation, which oversees Monticello, has previously called Jefferson’s paternity of Hemings's children a “settled historical matter,” some groups and family members have expressed reservations about the study. Mary Brady-Atkins, a 98-year-old descendant of Hemings, withdrew her consent prior to publication, citing concerns about her treatment during the research and lack of access to the material being published about her family. Additionally, the private Monticello Association, run by Jefferson’s descendants, continues to exclude Hemings’s descendants from membership and cemetery rights.

The Smithsonian, which receives substantial public funding, has been careful amid potential political sensitivities, particularly given the current administration’s reluctance to challenge the legacy of the nation’s founding fathers. An event to announce the findings was reportedly moved and closed to the press.

The research highlights broader trends in how genetic data is increasingly reshaping understanding of historical narratives, enabling deeper exploration into stories long obscured by time and incomplete records. As more archival materials related to Jefferson and Hemings become digitized and accessible, the findings contribute to ongoing national conversations about race, slavery, and American history.