Most scholars today believe that Thomas Jefferson had a lengthy affair with slave Sally Heming. Reasons commonly cited for belief are the 1998 DNA study, the Thomas Jefferson Memorial Foundation’s (hereafter, TJMF) investigation of the DNA study and relevant historical evidence, and the research of noted scholars. Problems abound. The DNA study shows merely that Jefferson is a possible candidate for paternity—one of many others carrying the Jefferson Y chromosome that Eston carried. The historical evidence prior to the DNA study was acknowledged by most scholars to be exiguous. Thereafter, nothing significant has surfaced. Yet historians today commonly state that the two sources of evidence, taken together, are sufficient to show probability or even great probability of paternity of Eston Hemings, and even all the other children of Sally Hemings. How does one add together biological data to historical data in a quantifiably measurable manner to show probability or high probability? It cannot be done.

In 1998, a DNA study titled “Jefferson Fathered Slave’s Last Child” was published in the prominent British weekly publication Nature.iThe study, however, showed merely that someone with the Jefferson haploid fathered Eston Hemings and that someone could have been Thomas Jefferson, or one of numerous other male Jeffersons.The scientists argued that the evidence, coupled with known historical circumstances, made Jefferson the most likely candidate for Eston’s paternity. The “simplest and most probable” explanation, in the “absence of historical evidence” for other candidates, is “Thomas Jefferson … was the father of Eston Hemings Jefferson.”ii The suggestion here is that the DNA evidence, itself unpersuasive, and the lack of historical evidence for other candidates, somehow add up, when together considered, to implicate Jefferson.

Then came the Thomas Jefferson Memorial Foundation’s committee report in 2000. It concluded, “The DNA study, combined with multiple strands of currently available documentary and statistical evidence, indicates a high probability that Thomas Jefferson fathered Eston Hemings, and that he most likely was the father of all six of Sally Hemings’s children appearing in Jefferson’s records.”

The study and the TJMF’s report set astir the media and historians. Newspapers across the nation wrote of the scientific “proof” of Jefferson’s sexual relationship with Hemings. Other media followed suit.iii Historians too were quick to change their minds on Jefferson’s uninvolvement. “Rarely in the writing of American history has the conventional wisdom about a debate reversed so completely,” writes R.B. Bernstein.iv

It is now commonplace merely to note uncritically that DNA results when added to the extant historical evidence implicates Jefferson. Gordon-Reed states in her C-SPAN Booknotes interview:

The results of a DNA test … came in to suggest that one of the descendants of Sally Hemings was, in fact, a Jefferson, and so it led a number of people—and myself included—to come to the conclusion that, coupled with the information that I write about and, you know, putting the DNA test together, that this story is true, as well-established as most—many more things in history have been established.v

E.M. Halliday writes: “In the autumn of 1998 careful DNA tests revealed a high scientific probability that Jefferson had indeed fathered the last one of Sally’s children, which along with circumstantial evidence strongly suggested that he fathered them all.”vi Andrew Burstein states, “Perhaps the DNA findings have not absolutely made Thomas Jefferson the father of his house servant’s children, but mounting circumstantial evidence makes him by far the most plausible father of these children, as most would now agree.”vii

The prevailing sentiment in all such instances is that the biological and historical evidence, added together, yield high probability. Jefferson is implicated, even though the DNA study shows only that Jefferson is a possible candidate for paternity, but that same possibility is applicable to all other Y-chromosome Jeffersons. If there are 10 viable candidates, all one can say biologically is that there is a likelihood of 0.10 that Jefferson is the father of Eston. One must turn to historical evidence, which is sinewy, slight, and circumstantial—a point Gordon-Reed conceded in her 1997 book on Jefferson and Hemingsviii—to begin to make more substantive probability assessments. One cannot, however, take an unpersuasive DNA argument and magically add it to scrimpy historical evidence. To do so, is to fall prey to the fallacy of artful addition.

Yet numerous scholars seem merely to assume that the two sets of data can be added together in some manner such that the probability of Jefferson’s involvement in an affair is thereby additively increased. That cannot be the case. If biological evidence should surface that implicates Jefferson with a great amount of probability, historical evidence is unneeded. Jefferson, then, would very likely be the father of Eston Hemings. Should overwhelming historical evidence surface that implicates Jefferson, then biological evidence is unneeded. In the present state of uncertainty, nothing other than agnosticism is warranted.

i Eugene A. Foster, M. A. Jobling, P. G. Taylor, P. Donnelly, P. de Knijff, Rene Mieremet, T. Zerjal, and C. Tyler-Smith, “Jefferson Fathered Slave’s Last Child,” Nature, 396, 5 Nov. 1998, 27. The statement that the molecular findings “provide evidence” for Thomas Jefferson’s paternity is misleading. The findings also provide evidence for many other male-line Jeffersons’ paternity. A more circumspect wording would be, The molecular findings are consistent with Jefferson being the biological father of Eston Hemings, along with the caveat that there are other possible fathers.

ii Eugene A. Foster, et al., “Jefferson Fathered Slave’s Last Child,” 27-8.

iii See David Murray, “Anatomy of a Media Run-Away,” The Jefferson-Hemings Myth: An American Travesty, ed. Eyler Robert Coates, Sr.(Charlottesville: The Thomas Jefferson Heritage Society, 2001), 37-46.

iv R.B. Bernstein, Thomas Jefferson (New York: Oxford University Press, 2003), 196

v http://www.booknotes.org/FullPage.aspx?SID=119003-1, accessed 10 August 2012.

vi E.M. Halliday, Understanding Thomas Jefferson (New York: HarperCollins Publishers, 2001), xi-xii.

vii Andrew Burstein, Jefferson’s Secrets: Death and Desire at Monticello (New York: Basic Books, 2005), 182

viii Annette Gordon-Reed, Thomas Jefferson and Sally Hemings: An American Controversy (Charlottesville: The University Press of Virginia, 1997), 226.