I haven't said much about this article in Science, Ancient DNA Links Native Americans With Europe, because it would be an understatement to say I'm digesting it. I would offer up a caution that using terms like "Europeans" and "East Asians" for populations which flourished ~25,000 years ago might be misleading. We are used to thinking of genetic distance in terms of space, but time is also a dimension to consider. Populations even without admixture or gene flow will have drifted in allele frequencies over so many generations. But I have to admit that it seems more and more likely that
most extant modern populations are combinations of lineages which diverged very early after the "Out of Africa" migration.
We see this clearly with South Asians, and now Europeans and Native Americans. The Reich lab has also found evidence of admixture in in Australians. The closer we look, the more amalgamation we see between disparate lineages. Using the elements of the present to reconstruct the patterns of the past is going to be a more daunting task than most would have guessed.