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.
With that, I want to talk about hair form. Early physical anthropologists grasped onto this characteristic because it is so easy to define and measure. Hair can be straight, wavy, curly, and tightly curly (“woolly”). Even within tightly curled hair, there is variation. The San Bushmen have “peppercorn hair,” which means its curl is tighter than that of their Bantu neighbors.
One assumption that many people make is that originally anatomically modern humans had tightly curly hair, rather like modern Africans. Additionally, the depictions of Neanderthals I’ve seen do not give them this form of hair. Though there are mutations that change hair form (no surprise they are shared with dogs and cats), looking at the minimal literature on this trait it seems that curliness is somewhat polygenic. It doesn’t segregate like a Mendelian trait.
Likely one reason that curly hair is presumed to be ancestral is that many of the Australo-Melanesian peoples exhibit similar hair form to Africans, and these people have long been thought to be more “ancient.” But this is a fallacy. The ancestors of the Andamanese and Negritos of Southeast Asia are no more ancient than those of the Han Chinese. All descend from the same group of people who pushed eastward around 50,000 years ago.
Until recently I had assumed that the best model for the indigenous people of South Asia, the “Ancient Ancestral South Indians” (AASI), were the Andamanese. And yet one group in south India, the Paniya, are ~75% AASI in their ancestry. Looking through photographs of this tribe with a keen eye toward hair form, though their hair is curly, on the whole, no individuals show extremely tight curls.
And of course, Australian Aboriginals famously, on the whole, do not have tightly curled hair. Most of them are wavy haired (though curlier hair form is more common on the northern coast).
Where does this leave us? Of non-African descendent populations, there are a diverse set of lineages. None of the people of West Eurasia have tightly curled hair. Of those to the east, only the Negritos of South and Southeast Asia, and the people of Melanesia do so. But the Australian Aboriginals, who are closer to Melanesians than any other population, do not have tightly curled hair (though the Tasmanians, who separated from the Aboriginals ~10,000, may have had so based on the photographs). The peoples of Northeast Asia and the Americas, do not have tightly curled hair, obviously.
The primary confound here is selection. Hair form is a polygenic trait. It is not unreasonable to think that the humans moving out of Africa would carry standing variation, and that selection for curlier hair in some tropical climates would result in convergent evolution. The ancestors of Papuans and Negritos then may have had wavy hair, and Australian Aboriginals simply maintained this.
Ultimately doing the same thing with hair that was done with pigmentation will probably answer the questions of ancestral-derived states.