Jefferson's descendants have gathered at Monticello each May for the best part of this century. They have the run of the Palladian mansion above Charlottesville and, with their cocktails, can drink in the views across the forests of Virginia to the Blue Mountains. They claim ancestry from Jefferson's two daughters who survived into adulthood, Martha and Mary. They form an exclusive club, the Monticello Association, with the right to be buried in the small estate graveyard alongside their ancestor, and they are white.
This weekend, they were joined by about 50 descendants of Hemings, some brought up as white, others as black. And even though the Jeffersons and Hemingses agreed to pose, intermingled, for an unprecedented "family" photograph at the mansion, the atmosphere was not always cordial and the mingling far from relaxed.
One of the two terraces was reserved for members of the Monticello Association. On the other, the Hemingses socialised mostly with each other. For many, it was the first time they had met not only Jefferson- descendants, but other members of their own clan.
The mood towards the Jefferson camp was gracious but determined. Many were visiting Monticello for the first time, inspecting the one-room houses where the slaves were housed, and the grand house. Some felt vindicated by the findings published in Nature magazine last year showing that Hemings' youngest son, Eston, was fathered by a member of the Jefferson family, probably the former president, but possibly his brother.
For a few it was a shock. The majority, though, said they had always been told, and believed, the story of Thomas Jefferson and Sally Hemings, the slave woman he visited at night and freed, with two of her children, in his will.
"I was raised knowing that it was true - this just let others know," said Justin Jefferson Boggs, a 20-year-old computer engineering student at the University of California at San Diego, who could pass for white. "But it was a great thing to know who you were descended from," he said. "It gives a great feeling of completeness."
Inside the Monticello Association, however, the trouble that had simmered since the DNA findings confirmed the link between the Jeffersons and the Hemingses was becoming evident. Lucian Truscott IV, who had campaigned for the Hemingses to be invited to this year's gathering, and who advocates their inclusion in the Monticello Association, was finding the going tough. The association had voted that afternoon to set up a committee to consider membership for the Hemingses and postpone any decision, probably until next year's reunion.
The author of that decision was Bob Gillespie, president of the association, who said that no genealogy had been kept for "slave children" and that it was important "not to rush to a rapid, ill-informed decision". The DNA findings had "presented a real problem".
But Mr Truscott told the assembled families: "The door being opened now is not going to close... What we've got," he said, "is not a real problem, but real cousins, and we've got an opportunity here."
The opportunity, of course, is to incorporate the history of slavery and the historical interaction of blacks and whites in America into the mainstream. Since the start of the year, tours of Monticello, run by the Jefferson Trust, have included information about the former president's slave- holdings and their lives on the estate. The Association, however, has been less receptive.
Jefferson, as Mr Truscott says, "owned 38 human beings on Independence Day when he wrote those beautiful words - `We hold these truths to be self-evident: that all men are created equal...' The right thing now is to show some common sense in welcoming these good people into our hearts and our family."