The findings came after a sample of DNA from Haley's nephew Chris Haley matched that of his distant cousin June Baff-Black, who lives in Wales and whose shared lineage starts in 17th century Scotland.
Until recently, Chris Haley had only word of mouth family history to show that his great, great-grandfather had been born of an African slave mother and white Scottish father, both of whom lived and worked on a slave plantation in the US.
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Instead Haley relied on the oral histories handed down from generation to generation as his primary source of ancestral information.
Chris Haley, from Washington DC, was introduced to Ms Baff-Black, who lives in South Wales, for the first time on Saturday at the Who Do You Think You Are?
Olivier van Calster, managing director of uk, said: "As Alex Haley knew only too well, at its core, any family history is a combination of established facts and reasonable assumptions.
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But of course I had no idea I was linked in some way to his ancestors. "Chris and I have got so much in common – from what we like to the way we write and the fact we both love theatre." Mr Haley, 46, an actor and slavery historian, said: "I wish Alex had had DNA technology at his disposal.
There has been a lot of controversy about his use of our oral history and these findings confirm what he wrote in Queens.
DNA testing is a relatively new technology for genealogists, allowing them to trace the paternal or maternal line by studying either the 'Y-chromosome', which is passed from father to son, or 'mitochondrial DNA', which is passed from mother to daughter.
The DNA service from uk compares the results from people with others who have carried out the same test, identifying possible matches from around the world."This shows we are really more similar than we believe, whether we are black or white, and we should put aside our superficial differences and focus on what we are as human beings." The phenomenal success of Haley's novel Roots, and the television drama on which it was based, led to a world wide interest in genealogy, particularly among African-Americans, many of whom felt their slave backgrounds had robbed them of their rightful history and identity.