By Jeanna Smialek, Bloomberg News
The earliest people to enter North America came in three waves rather than a single migration, according to evidence comparing the DNA of Native groups in Canada and South America with those in Siberia.
Scientists have believed the Americas were populated by ancestors who entered through an Asian-American land bridge that existed in northern Canada 15,000 years ago. Wednesday's announcement, reported in the journal Nature, adds evidence to a long-fought debate in support of the multiple-migration theory.
By comparing the genomes of groups on both ends of the pattern, investigators were able to tease out hints about the added migrations, said Nick Patterson, a researcher at the Broad Institute of the Massachusetts Institute of Technology and Harvard Medical School in Boston.
"Genetics is able now to make some contribution, fairly limited, to looking at ancient human history," said Patterson, a computational biologist at the institute's Medical and Population Genetic Program in Cambridge, Mass.
The study, led by geneticist David Reich of Harvard Medical School, analyzed DNA autosomes, which contain genetic data from all of a person's ancestors. Past studies that pointed to a single migration examined mitochondrial DNA, which contains only maternal genetic material.
No one from the United States would share samples that had the necessary consents for use, said Andres Ruiz-Linares, a University College London geneticist who co-authored the report. While that didn't skew the research, it left researchers with an incomplete picture.
While the genetic evidence can't show precisely how migration occurred, or even date when they occurred, Patterson said, researchers think that all three flows came across the Siberian land-bridge because that theory is consistent with their results.
Future genetic studies could unlock more secrets about how today's peoples are ancestrally tied, Patterson said.