Assistant Village Idiot posted a link to this very interesting interactive map and timeline of human worldwide migration as suggested by mitochondrial DNA evidence. Most of it was what I'd generally gathered from reading over the years, but there were two discontinuities that were new to me. First, the Mt. Toba volcanic catastrophe of about 74,000 years ago cut off a lot of people who had managed to migrate east through South Asia to Indonesia. After that, they radiated into Southeast Asia and Australia, but also back the way they came, all the way to Europe, reversing the direction of the pre-Toba migration.
Second, the East Asians made it up to the Bering Strait and crossed into North America between 25,000 and 22,000 years ago, including a significant group that arrived on the mid-Atlantic coast. Between 22,000 and 15,000 years ago, however, an ice age wiped out nearly all settlements and movement north of the 55th Parallel, cutting off the New World from Asia. When things warmed up, there was a whole new migration from Asia, this time mostly hugging the west coast of the Americas and spreading all the way down into the southern hemisphere. In the meantime, the old settlements on the mid-Atlantic coast also spread down into South America, but mostly hugging the east coast.
I thought of the map today because of a Maggie's Farm link to a Smithsonian article about the long-simmering debate over whether the Clovis culture represented the first arrival of people in North America about 13,500 years ago. The "science was settled" for quite some time, but more recent archaeology has led many to open their minds to the possibility of pre-Clovis cultures. There may have been two major migrations, widely separated in time and geography.