Washington, Mar 14 : A new study of DNA suggests that nearly all Native Americans can trace part of their ancestry to just six women whose descendants immigrated around 20,000 years ago from Asia.
Researchers said that those women left a particular DNA legacy that persists to today in about 95 percent of Native Americans.
The finding does not mean that only these six women gave rise to the migrants who crossed into North America from Asia in the initial populating of the continent, said study co-author Ugo Perego from the Sorenson Molecular Genealogy Foundation in Salt Lake City and the University of Pavia in Italy, reports the journal PLoS One.
He said that the women lived between 18,000 and 21,000 years ago, though not necessarily at exactly the same time.
In the study, the team 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. So it follows a lineage that connects a person to his or her mother, then 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.
The six "founding mothers" apparently did not live in Asia because the DNA signatures they left behind aren't found there, Perego said.
They probably lived in Beringia, the now-submerged land bridge that stetched to North America, he said.
The study is published in the journal PLoS One.