The genomes of ancient Alaskans reveal clues to human settlement in the Americas

a human baby genome sequence that lived in Alaska about 11,500 years ago. This is the first direct genomic evidence that all Native American ancestors date back to the same source population during a single migration event in the late 1980s.
although it is generally believed that humans first settled in the Americas through the Bering Continental Bridge, the exact time and manner are still controversial. In 2013, the remains of two human babies, dating back about 11,500 years, were found at the site of the Xiangyang River in Alaska. Eske Willerslev of the University of Copenhagen in Denmark and colleagues sequenced the entire genome of one of the babies, USR1;
they compared USR1 with previously measured contemporary and ancient Native American genomes and found that the baby was most recently related to today's Native Americans. They argue that USR1 represents a very different population, known as the "ancient white man", whose ancestors with other Native Americans originated in a single initial population that was first separated from East Asians about 36,000 years ago, but whose gene flow continued until about 25,000 years ago.
these findings are consistent with the so-called Bering Retention Model, according to which offspring of a source population lived in Eastern Bering until at least 11,500 years ago. But by then, another branch of Native Americans had settled in glacier-free areas of North America and divided into two groups, eventually becoming the ancestors of most Native Americans. (Source: Science Network Zhang Zhang)