Sequencing Thomas Jefferson’s D.N.A. Confirms Historical Evidence

The New York Times is reporting on a Smithsonian study to be published in book form this week that:

• completely sequenced Thomas Jefferson’s D.N.A.
• found that it matched fifth-generation descendants of both Martha Jefferson and Sally Hemings in the percentage to be expected of descendants of Thomas Jefferson.

The book is History by a Hair: Thomas Jefferson, Sally Hemings & Solving a 200-Year-Old Mystery, by Richard Kurin.

When Kurin launched this study fifteen years ago, the sort of genetic testing it ended up using wasn’t yet available. Extracting a complete genome from hair was thought to require follicles, not a snipped lock, plus a lot of luck that the molecules hadn’t degraded.

Another bump in the road was when strands of hair found in Jefferson’s edited Bible turned out not to be his, based on their mitochondrial D.N.A.

But Monticello was able to provide another hair sample, said to be clipped from Jefferson’s head during his last illness in 1826. That produced a match with the descendants who had provided D.N.A. samples.

Back in 1998 Nature published a study led by Eugene A. Foster which found a Y-chromosome match between patrilineal descendants of one of Jefferson’s paternal uncles and a patrilineal descendant of Eston Hemings. The same test found that chromosome was different for patrilineal descendants of Jefferson’s nephews Patrick and Samuel Carr and of Thomas Woodson, believed by some relatives to be a Jefferson child.

Already there was strong historical evidence for Jefferson’s paternity of Eston Hemings, his brother Madison Hemings, and the other siblings Madison named. The Y-chromosome findings were entirely consistent with Madison’s description of the family in 1873. Most historians considered the question settled.

Some Jefferson “defenders,” however, responded to the Foster study by proposing Thomas Jefferson’s brother Randolph or his sons as a possible source for that patrilineal D.N.A. Those men had never been publicly linked to Sally Hemings before.

This new analysis looked at Thomas Jefferson’s D.N.A. distinct from Randolph’s, removing that brother and his sons from consideration. 

This study also involved more descendants, not just those with a patrilineal connection. In fact, the descendant in the study sharing the most D.N.A. with the third President (5%) is a descendant of Sally Hemings, not of Martha Jefferson.