Dr. Ben Potter, of the University of Alaska, discovered the girls' bones and other remains at the Upward Sun River site in Alaska's Tanana River Valley in 2006. The area was occasionally a stopping point for settlers arriving from Siberia. The girls' remains rested atop a hearth.

An extensive DNA search of the remains determined that the girls had different mothers and also found a type of mitochondrial DNA (which passes to a child only through the mother) that is still found in Native Americans living today.

The oldest known remains found in North or South America was the Anzick Child, who lived 12,700 years ago. Another very old skeleton found in the Pacific Northwest was the Kennewick Man, whose remains were recently reburied in Native American terms after decades of dispute.

Both of those people belonged to what archaeologists call the southern branch of ancestral groups, people that settled in the U.S. and in Central and South America after traveling from their homes in what is now eastern Russia. The settlers referred to as the northern branch settled in what is now Canada and in a couple of specific areas in the U.S.

The newly found remains belonged to neither branch but were part of a previously unidentified group of people who lived in a place called Beringia (also known as the Bering Land Bridge), which 20,000 yeas ago was a land mass that included both Alaska and Siberia. About that same time, the Beringians split off genetically from the other people living in the area, and it is that bloodline that the archaeologists found in the bones of the girls in the Tanana River Valley. It wasn't until 4,000 years later that the northern and southern branches came into existence.