Nearly all of today's Native Americans in North, Central and South America can trace part of their ancestry to six women whose descendants immigrated around 20,000 years ago, a DNA study suggests.

Those women left a particular DNA legacy that persists to today in about about 95 percent of Native Americans, researchers said.

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.

The women lived between 18,000 and 21,000 years ago, though not necessarily at exactly the same time, he said.

The work was published this week by the journal PLoS One. Perego is from the Sorenson Molecular Genealogy Foundation in Salt Lake City and the University of Pavia in Italy.

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.

Connie Mulligan of the University of Florida, an anthropolgist who studies the colonization of the Americas but didn't participate in the new work, said it's not surprising to trace the mitochondrial DNA to six women. "It's an OK number to start with right now," but further work may change it slightly, she said.

That finding doesn't answer the bigger questions of where those women lived, or of how many people left Beringia to colonize the Americas, she said.