четверг, 22 марта 2018 г.

The whiteboard

David Reich’s book, Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past, is coming out next Tuesday (see here). Chapter 6 has the potentially controversial title The Collision that Formed India, and indeed I know for a fact that Bronze Age steppe pastoralists, who seem to induce panic attacks amongst a lot of people, and especially Out-of-India supporters, will get a big hat tip in this chapter.
But I can’t really say more than that until after the book launch. So in the meantime, let’s focus on this intriguing photo of a messy whiteboard that was published in the New York Times this week along with a feature on the Reich Lab’s work with ancient DNA. The version below was edited by me to highlight and fill in a few details. The original can be viewed by scrolling down here.



Clearly, this is a mixture and migration model for Central Asia and surrounds covering the crucial period 2200-1500BCE, when, according to a consensus amongst historical linguists, waves of Indo-European speakers moved into the region from the steppes. It’s probably from a jam session about an upcoming ancient DNA paper. Here’s my interpretation of the model:



– nodes 1, 2, 3 and 4 track the migration of Bronze Age pastoralists from the Pontic-Caspian steppe deep into Central Asia, while nodes B and C follow the expansion of Neolithic farmers from east of Anatolia (probably from somewhere in present-day Iran) into Central and South Asia (nodes 1 and B aren’t actually visible in the original pic, but must be there, and more or less where I marked them)
– node 2 probably represents the formation of late Corded Ware Culture (CWC) populations across Northern Europe around 2900 BCE, via the mixture of Yamnaya or Yamnaya-related steppe pastoralists (node 1) with European farmers, who were themselves a mixture of Anatolian farmers and Western European Hunter-Gatherers (WHG)
– Sintashta and Andronovo_NW at node 3 derive directly from the mixture event at node 2, so either they’re offshoots of late CWC or a closely related population
– intriguingly, and perhaps crucially, nodes 2 and 3 only take one pulse of admixture from node 1 (red X), while the branch leading to Andronovo_SE at node 4 takes two such pulses, with one apparently later than 1900 BCE, possibly suggesting that Andronovo_SE was more Yamnaya-like compared to late CWC, Sintashta and Andronovo_NW
– moreover, the branch leading to Andronovo_SE absorbs significant admixture from Western Siberian Hunter-Gatherers (West_Siberian_HG) and possibly a Central Asian ghost population, no doubt resulting in a further reduction of Anatolian farmer and WHG ancestry ratios in Andronovo_SE compared to Sintashta and Andronovo_NW
– thus, Andronovo_SE, unlike Sintashta, might fit the bill statistically as enough Yamnaya-like to be the Yamnaya-related Bronze Age steppe pastoralists who “crashed” into India during the Bronze Age (see here), although, admittedly, this isn’t actually shown on the whiteboard
– on the other hand, if, perhaps, the model includes a migration edge from node 1 to B, then this would suggest that Yamnaya-related ancestry arrived in South Asia with a very different population than Andronovo_SE, and possibly much earlier than 1500 BCE, but we don’t know because David Reich is (strategically?) blocking that part of the whiteboard.



Also worth noting is that there’s actually nothing about India in the model. The most proximate region that gets a mention is “Turan/Northern South Asia”. So should we be concerned that the supposedly imminent publication of ancient DNA from Rakhigarhi and other Indian prehistoric sites has been pushed back indefinitely, perhaps for political reasons? Normally I’d say no, but in recent weeks I’ve been hearing rumors that this is indeed the case.
See also…
Late PIE ground zero now obvious; location of PIE homeland still uncertain, but…

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