From [HERE] President Obama’s biography — son of a black father from Kenya and a white mother from Kansas — has long suggested that unlike most African-Americans, his roots did not include slavery.

Now a team of genealogists is upending that thinking, saying that Mr. Obama’s mother had, in addition to her European ancestors, at least one African forebear and that the president is most likely descended from one of the first documented African slaves in the United States.

The findings are scheduled to be announced on Monday by Ancestry.com, a genealogy company based in Provo, Utah. Its team, while lacking definitive proof, said it had evidence that “strongly suggests” Mr. Obama’s family tree — on his mother’s side — stretches back nearly four centuries to a slave in colonial Virginia named John Punch.

In 1640, Mr. Punch, then an indentured servant, escaped from Virginia and went to Maryland. He was captured there and, along with two white servants who had also escaped, was put on trial. His punishment — servitude for life — was harsher than what the white servants received, and it has led some historians to regard him as the first African to be legally sanctioned as a slave, years before Virginia adopted laws allowing slavery.

Historians say there was a trade in human labor, of both whites and blacks, during this period in American history. There were also some free African-Americans. Beginning around 1617, indentured servants were bought and sold, as were debtors, in the Chesapeake Bay region, said Ira Berlin, a University of Maryland professor and expert in the history of slavery. But while those people were in an “unfree condition,” he said, historians cannot pinpoint a date for the beginning of the slave trade.

“What makes the John Punch case interesting is here is a guy who is definitely a slave,” said Professor Berlin, who did not participate in the examination of the president’s ancestors.

The Ancestry.com team used DNA analysis to make the connection, and it also combed through marriage and property records to trace Mr. Obama’s maternal ancestry to the time and place where Mr. Punch lived. The company said records suggested that Mr. Punch fathered children with a white woman, who passed her free status on to those children, giving rise to a family of a slightly different name, the Bunches, that ultimately spawned Mr. Obama’s mother, Stanley Ann Dunham.

The findings come as more and more Americans are discovering their own mixed-race heritage. Elizabeth Shown Mills, a former president of the American Society of Genealogists, said the Internet, coupled with the ease of DNA testing and heightened interest among both amateur and professional genealogists, was helping to reveal the extent of racial intermingling over the centuries.

“It is becoming increasingly common now because people are discovering it,” Ms. Mills said. “In the past, very few records were available. Very few people made the effort to do the research.”

The Ancestry.com team spent two years examining Mr. Obama’s mother’s past, focusing on the mixed-race Bunch line. The researchers said that over time, as the Bunches continued to intermarry, they became prominent landowners in colonial Virginia and were known as white.

“We sort of stumbled across it,” said Anastasia Harman, the lead researcher. “We were just doing general research into the president’s family tree, and as we started digging back in time, we realized that the Bunch family were African-American.”

There is no evidence that Ms. Dunham had any inkling that she might have had African-American ancestry, said Janny Scott, her biographer. By the mid-1800s, according to a 2007 article in The Chicago Sun-Times, one of Ms. Dunham’s Bunch ancestors had a son who fought for the Confederacy in the Civil War.

The Ancestry.com group traced two major Bunch family branches, one that lived as white and stayed in Virginia for generations and another that left for the Carolinas. In North Carolina, the Bunches were recorded as “mulatto” in early records, and their descendants are also the president’s cousins.

Mr. Obama descends from the Virginia branch, which eventually migrated to Tennessee, where his great-great-great-great-grandmother Anna Bunch was born. Her daughter Frances Allred, who was born in 1834, moved to Kansas. Four generations later, in 1942, with the family still in Kansas, Mr. Obama’s mother was born.

But the research left open a question: Was John Punch, the slave, a Bunch ancestor? Because records have been destroyed, there is no definitive proof.

Still, some factors led Ms. Harman and her group to a conclusion. The surnames were similar. There was DNA evidence showing that the Bunches had sub-Saharan African heritage. And a very small number of Africans were living in Virginia in the mid-1600s. All that convinced the team that the nation’s first black president was descended from Mr. Punch.

“The odds, based on what does actually survive, strongly suggest that President Barack Obama is a descendant (he would be the 11th great-grandson) of the first enslaved African in America,” Ms. Harman and her team wrote in a research paper that Ancestry.com intended to release on its Web site on Monday.

The team shared its findings with The New York Times, which consulted two independent genealogists — Ms. Mills, who specializes in Southern genealogy, and Johni Cerny, who specializes in black ancestry — about the findings. Both said there was no way to be certain of the Punch-Bunch connection. But both also said the Ancestry.com team made a solid case.

“The research, I am convinced, is sound,” said Ms. Mills, who also reviewed the findings at Ancestry.com’s request. “The P and the B are virtually meaningless in historical context. What matters is the historical evidence that can be mustered to place the same people in the same area.”

Ms. Cerny was more skeptical but said the research team’s careful wording was appropriate. “I’m sure people will be tantalized and try to prove or disprove it,” she said. “But what they’re saying is very safe and appropriate. I would be tempted myself to try to make that connection.”

One reason the Ancestry.com team could make the connection was the Bunch family itself. The extended family maintains an online database that traces the family tree. It is supplemented by DNA testing showing that the men in the family have genetic markers consistent with sub-Saharan African descent. The Ancestry.com paper said the Bunches’ particular DNA profile was common in Cameroon.

“I consider myself Caucasian, but I find that my mixed-race roots go way back,” said Mark Bunch, who administers the Bunch family project.

Mr. Bunch, 53, the finance director for a community hospital in the agricultural town of Othello, in eastern Washington State, learned of the project several years ago from a cousin. He bought a home DNA test kit, swabbed the inside of his cheek three times and sent it off for analysis. What came back — a genetic blueprint that included sub-Saharan African roots — surprised Mr. Bunch. Then came another surprise: President Obama was a distant cousin.

“I’m his fifth cousin twice removed,” Mr. Bunch said. “Of more surprise was the African Y chromosome. The relationship to President Obama was kind of the icing on the cake after that.”