On the doorstep of India

One of the most remarkable discoveries in the recent Narasimhan et al. 2018 preprint has to be the presence of what are essentially Eastern European migrant populations living within the Inner Asian Mountain Corridor (IAMC) during the Middle to Late Bronze Age (MLBA). Remarkable for so many reasons, but seemingly under-appreciated by a lot of people, judging by the online discussions that I’ve seen on the preprint, and even, I’d say, the authors themselves.
Narasimhan et al. labeled these groups as belonging to the “forest/steppe MLBA” complex (for instance, see the main figure from the preprint here). This is indeed what they are in terms of their genetic structure, but certainly not geography, because the IAMC is well south of the steppe. Thus, in my Principal Component Analysis (PCA) I’m going to label them as part of the “post-steppe herder expansion Turan” complex.
Strikingly, most of these people cluster with Bronze Age Eastern Europeans, and even some Bronze Age Central Europeans. They’re also sitting very close to the more easterly present-day Slavic-speakers from Russia and Ukraine, and indeed closer to the bulk of the European cluster than some present-day Turkic and Uralic groups from the Volga-Ural region. Even I never predicted such an outcome. Sure, I was expecting to see ancient genomes from South Central Asia with some very heavy steppe influence, but not this. The relevant datasheet is available here.

Two of the MLBA IAMC individuals are from Kashkarchi in the Ferghana Valley, in what is now Uzbekistan, and basically on the doorstep of the Indian subcontinent. I’ve made special mention of them on the plot, and I’ve also highlighted a pair of individuals from the Bronze Age Central Asian sites of Gonur Tepe and Shahr-i Sokhta, who are, in all likelihood, unadmixed migrants from the Indus Valley (for more on that, see here).
It’s surely not a coincidence that the ancient and present-day South Asians on the plot (including those from Pakistan’s Swat Valley dated to the Bronze and Iron Ages) form an almost prefect cline between these two pairs of individuals. It’s also surely not a coincidence that the MLBA IAMC groups are rich in Y-haplogroup R1a-M417, and in particular its R1a-Z93 subclade, which is today an especially frequent marker in Indo-European-speaking South Asians.
Forget about the pre-MLBA populations from the forests, steppe, or IAMC, like those represented by Dali_EBA; they’re practically irrelevant to this story. How do I know? Because they have little to no impact on the above mentioned cline. And this can be easily verified with mixture models based on multiple Principal Components (PCs) and formal statistics (for instance, see here).

Clearly, many populations in South Asia, particularly those speaking Indo-European languages, derive the bulk of their steppe-related ancestry from the peoples of the MLBA IAMC, and/or their very close relatives. And if you do believe that this inference is just based on coincidences, then I’m sorry to say this, but obviously a new, much less mentally challenging, hobby or profession beckons. All the best with that.
Just to help put all of this in a geographic perspective, here’s a topographical map of Eurasia. I’ve marked the location of the Ferghana Valley. The close relatives of Kashkarchi_BA most likely skirted their way around those winding high mountains and slipped into India via the Khyber Pass, which I’ve also marked on the map.

And the rest, as they say, is history, including the history described in the ancient Indo-Aryan Sanskrit texts known as the Vedas. I’m sure we’ll soon be learning about these events in great detail when many more ancient samples from Pakistan and, hopefully, the first ancient samples from India, are published.
Citation…
Narasimhan et al, The Genomic Formation of South and Central Asia, Posted March 31, 2018, doi: https://doi.org/10.1101/292581
See also…
Late PIE ground zero now obvious; location of PIE homeland still uncertain, but…

Source