Van Hall, associate professor of history at the University of Pittsburgh, said it is unlikely that most of the men on the list had black ancestry because historians know their genealogy pretty well.
While he concedes he hasn't researched the issue, Larry Glasco, also an associate professor of history at Pitt, is also skeptical of the stories.
"I would guess if [the stories] were really true we'd have heard a lot more about them," Dr. Glasco said. "There would have been a lot more written about them in professional research literature."
However, Marsha Stewart doesn't need any professional research. Mrs. Stewart, a 60-year-old black woman who teaches in suburban Detroit, said Mr. Harding is her cousin. She said it's something the family always has known but didn't publicly talk about.
Several of the claims that these presidents were of mixed racial heritage came from political opponents in an attempt to smear them. For example, President Lincoln, described as being dark with coarse hair, was depicted in a cartoon drawing by rivals as "Abraham Africanus the First."
"That's not an uncommon occurrence in American politics," said Russell Riley, presidential scholar at the University of Virginia's Miller Center of Public Affairs. "Because race is such a sensitive issue in American politics, it is an easy target for an unscrupulous campaigner to make a claim that somebody has a particular ancestry that the majority of the population is less likely to support."
Mr. Riley said with today's DNA mapping techniques it would be easy to prove or disprove these claims.
There was no such thing as DNA mapping when the late historian J.A. Rogers wrote his book, "Five Black Presidents," self-published in 1965, which serves as the basis for most of the more recently published works on the subject.
"Virtually, all we know came from J.A. Rogers," said Dr. Vaughn, who based his chapter on black presidents on Mr. Rogers' research and that of Dr. Auset Bakhufu. Dr. Bakhufu's 1993 book "The Six Black Presidents Black Blood: White Masks" includes Eisenhower.
Racial heritage of six former presidents is questioned
