Ancestry.com said the maternal line traces back to one of the first documented African slaves in the United States. The firm said Obama could be the 11th great-grandson of John Punch, an African slave in colonial Virginia. Punch is believed to have had children with a white woman, starting a line that led to Obama's mother.
The White House declined comment Monday.
The Ancestry.com team used DNA analysis and marriage and property records to trace Obama's maternal ancestry. The firm says it can't establish a definitive link because of gaps in family history. Researchers are missing a record connecting Punch to a presumed son who by his early 20s owned 450 acres and grew tobacco in Virginia.
The records pick up when a grandson of Punch petitioned a court to marry a white woman - and was turned down, presumably because the grandson appeared of mixed-raced heritage, said Elizabeth Shown Mills, a former president of the American Society of Genealogists.
The Ancestry.com findings make for a tantalizing tale that wasn't uncommon in early colonial Virginia, and the team probably got it right, Mills said. "They did the best job possible," said Mills, who reviewed the findings at Ancestry.com's request.
Ancestry.com said its team spent two years exploring Obama's maternal line. The puzzle starts with Punch, who is presumed to have arrived in Virginia around 1640 from West Africa, initially as an indentured servant obligated to work for years to pay for his passage.
"He jumped the gun and took off," Mills said. Punch was recaptured and made a slave for life. His punishment was tougher than white servants received for absconding, leading historians to call him the first African to be enslaved years before Virginia legalized slavery.
Nothing is known about Punch's presumed relationship with a white woman. But his landowner son is presumed to be John Bunch, either because the mixed-raced family changed its name or because records transcribed it incorrectly, Shumway said. Researchers were able to make a definitive connection between the successive Bunch family line and Obama's mother, Stanley Ann Dunham, who died in 1995.