"It is accepted by most scholars that Thomas Jefferson had a lengthy affair with his slave Sally Hemings and fathered at least one of her children. This conclusion is based on a 1998 DNA study published in Nature and on the work of historian Annette Gordon-Reed, assumed by many to be the last word on the subject. But as author M. Andrew Holowchak argues compellingly in this eye-opening investigation, the DNA evidence is inconclusive and there are...