A University of California study dismisses the popular idea that Native Americans draw their genetic heritage from Polynesians or European peoples. It says the first humans to reach the Americas came from Siberia in a single group some 23,000 years ago, at the height of the last Ice Age. On their way to Alaska, they hung around in the northern regions for a few thousands of years before moving deeper into North and South America.
There is some uncertainty in the dates of the migration and the divergence between the northern and southern Amerindian populations. But as we get more ancient genomes sequenced, we will be able to put more precise dates on the times of migration.