The above chart is from The Simons Genome Diversity Project: 300 genomes from 142 diverse populations. The basic outlines of this tree were evident as far back as L. L. Cavalli-Sforza. But there were always small details that caused issues. In particular, were East Asians a more natural clade with Australasians or with Europeans? Today with both ancient DNA and whole-genome analyses two things are clear which might have been confounding earlier analyses:
- There has been gene flow between many East Asian and European populations. If you look closely at the ancient DNA work it is clear that East Asian gene flow is present in Mesolithic hunter-gatherers. Conversely, many northern Chinese have show low levels of West Eurasian ancestry (I suspect mediated through Mongols and Turks).
- The peoples of Australasia have Denisovan ancestry, which is distinct from anything found in East Asians and Europeans (small trace proportions of Denisovan in the former notwithstanding).
With these considerations accounted for, it seems clearer that the peoples of Oceania and East Asia descend from a common group that pushed from the west. And, the most ancient substratum in South Asia is also part of this broad family of peoples, who diversified in the period between 45 to 55 thousand years before the present. This is in contrast to the peoples to the west, who gave rise to Ice Age Europeans, Middle Easterners, and more distantly the “Ancient North Eurasians” who seem to be the first settlers of Siberia.
To understand the context for the emergence of characteristics and traits one has to understand the demographic histories and relationships between people. We are coming close to establishing the latter with good certainty for most groups. Though the sea levels separated New Guinea from Australia only within the last ~10,000 years, genetic work suggests that the differentiation between highland Papuans and Australian Aboriginals long predates this. If I had to hazard a guess I’d suggest that the huge ecological differences were probably critical in reducing gene flow between the wet and warm highlands of Sahul, and the broad deserts that occupied what became Australia.