A new study of DNA suggests nearly all Native Americans can trace part of their ancestry to just six women, whose descendants immigrated to North, Central and South America as much as 20,000 years ago.
According to the study published this week by the scientific journal PLoS One, researchers believe the women left a DNA legacy that can be found in about 95 percent of native people throughout the Americas.
The study said the finding does not mean those six women were the only ancestors of the migrants who populated the Americas from Asia.
Researchers said the women probably did not live in Asia because the DNA signatures they left behind are not found there. They likely lived on Beringia, a now-submerged land bridge that once connected Asia and North America.
The "founding mothers" are believed to have lived between 18,000 and 21,000 years ago, though not necessarily at the same time, said study co-author Ugo Perego.
Perego is from the Sorenson Molecular Genealogy Foundation in Salt Lake City and the University of Pavia in Italy. He said the study confirms previous indications of six founding mothers.
Perego and his colleagues traced the history of a particular kind of DNA that represents just a tiny fraction of the human genetic material and reflects only a piece of a person's ancestry.
This DNA is found in the mitochondria, the power plants of cells. Unlike the DNA found in the nucleus, mitochondrial DNA is passed along only by the mother. It follows a lineage that connects a person to his or her mother, the mother's mother, and so on.
The researchers created a family tree that traces the different mitochondrial DNA lineages found in today's Native Americans. By noting mutations in each branch and applying a formula for how often such mutations arise, they calculated how old each branch was. That indicated when each branch arose in a single woman.
However, an expert unconnected with the study said the findings left some questions unanswered.
University of Florida anthropologist Connie Mulligan, who studies the colonization of the Americas but didn't participate in the new work, said it is not surprising to trace the mitochondrial DNA to six women. But Mulligan said the bigger questions of where those women lived and of how many people left Beringia to colonize the Americas remain unanswered.
The estimate for when the women lived is open to question because it is unclear if the researchers properly accounted for differing mutation rates in mitochondrial DNA, she said. Further work could change the estimate, she said.
From NPR and wire reports