There is a fairly new paper in PLoS on the colonization of the New World. It is the latest in a series of attempts to synthesize biogeography, climate change related paleoenvironmental reconstruction, genetics, and archaeology.
The authors draw these conclusions:
These results support a model for the peopling of the New World in which Amerind ancestors diverged from the Asian gene pool prior to 40,000 years ago and experienced a gradual population expansion as they moved into Beringia. After a long period of little change in population size in greater Beringia, Amerinds rapidly expanded into the Americas ≈15,000 years ago either through an interior ice-free corridor or along the coast. This rapid colonization of the New World was achieved by a founder group with an effective population size of ≈1,000-5,400 individuals. Our model presents a detailed scenario for the timing and scale of the initial migration to the Americas, substantially refines the estimate of New World founders, and provides a unified theory for testing with future datasets and analytic methods.
One of the problems I see in this sort of analysis is placing the evinced genetic splits in populations in space. This paper does a reasonably good job at arguing for an early split in Asia and subsequent population changes happening in the New World. However, if we change the timing of when the Ice Free Corrider was available to facilitate the movement of people, or if we change the rate of DNA mutation that is used to place population events in time, then the model may change fundamentally. I do not have lot of faith in the estimates used for DNA mutation rates.
Nonetheless, this is a good, the best so far, synthesis of the available data with new information added.
Also interesting is the fact that PLoS has a means of commenting on papers published in this Open Access journal. Go visit the paper (link below) and add your opinions!
Kitchen, A., Miyamoto, M.M., Mulligan, C.J., Harpending, H. (2008). A Three-Stage Colonization Model for the Peopling of the Americas. PLoS ONE, 3(2), e1596. DOI: 10.1371/journal.pone.0001596