NEW YORK, Feb. 25 -- The Rev. Al Sharpton, the prominent civil rights activist, is descended from a slave owned by relatives of the late senator and one-time segregationist Strom Thurmond, a genealogical study released Sunday reported.

"It was probably the most shocking thing of my life," Sharpton said of learning the findings, which were requested and published Sunday by the New York Daily News. He called a news conference to respond publicly to the report. "I couldn't describe to you the emotions I have had . . . everything from anger to outrage to reflection to some pride and glory."

Sharpton, 52, said he had suspected that his forebears may have been slaves but had never attempted to confirm that or find out any details.

"I had never really traced my family history, particularly on my father's side, since my parents separated when I was going on 10 years old," he said.

The newfound knowledge that his great-grandfather was a slave, Sharpton added, gave him a new perspective on his life.

"You think about the distance that you've come, you think about how brutal it was, you think about how life must have been like for him. And then you start wondering whether or not he would be proud or disappointed in what we have done," Sharpton said, with his eldest daughter, Dominique, 20, at his side.

The revelation was particularly stunning for the juxtaposition of the two men's public lives.

Sharpton, known for his fiery rhetoric and a tendency to intervene as an advocate in racially charged incidents, ran for president in 2004 on a ticket promoting racial justice. Thurmond made his own bid for the presidency in 1948, promising to preserve racial segregation, and in 1957 he filibustered for more than 24 hours against a civil rights bill.

After his death in 2003, though, it became clear that Thurmond had a complicated history with issues of race. A 78-year-old retired schoolteacher, Essie Mae Washington-Williams, revealed that she was the offspring of his extramarital relationship with his family's black housekeeper.

"In the story of the Thurmonds and the Sharptons is the story of the shame and the glory of America," Sharpton said Sunday.

The genealogy study was produced by researchers for the Web site Ancestry.com. Daily News reporter Austin Fenner initially asked them to research his own roots. He then approached Sharpton and asked if he would permit an investigation of his family history as well, for use in a story. Sharpton agreed. Neither the Daily News nor Sharpton paid for the research.

The research was led by chief Ancestry.com genealogist Megan Smolenyak, who was also the lead researcher for the 1997 PBS series "Ancestors" and has written several books on the subject. She was assisted by researchers including Tony Burroughs, who has been honored by the National Genealogical Society. They used documents including census, marriage, death and military records over a three-week period to examine Sharpton's family roots.