Afarensis has a long post worth reading about new discoveries relating to the peopling of the Americans. This is a controversial topic, Moira Breen has been covering this issue for several years now in relation to the famous Kennewick Man. But, this caught my eye:
Still, not all scientists are convinced that the variations found in the skulls are proof of multiple migrations to the Americas. "There is a huge amount of variation among the first Americans, more than you see among any other population outside of the Pacific," said Joseph Powell, an anthropologist at the University of New Mexico in Albuquerque. "Much of that is genetic, and it comes from the fact, I think, that these first Americans had very small colonizing populations, and they have a great degree of genetic variation due to genetic drift."
I think what this person is trying to say is that there were multiple founding events, and genetic drift within each group resulted in very different characters across groups. At this point, the scientist in question asks us to believe that these small populations would maintain their substructure for many generations? I don't buy it. Overall, genetic drift on a massive scale (bottleneck) tends to reduce variation. Migration between small groups also tends to homogenize differences between groups quickly when the numbers are small, as is the case when genetic drift rapidly results in intergroup variation because of founder effects. I don't necessarily believe that morphology implies phyolgeny here, human groups can exhibit a lot of variation in response to selection, and I would still lean that way. It isn't like human populations stand still, so what if skulls 10,000 years ago cluster with modern Melanesians and Africans? These groups have changed too. I actually probably lean more toward Powell's conservative hypothesis, I am just bothered by the recourse to genetic drift as a deus ex machina.