I'm sorry if someone has already posted this here. I think it's a useful summary of the topic, although of course one needs to evaluate the topic after publication by D.Reich
Lecture by Prof. David Reich – “The Genetic History of the Southern Arc: A Bridge between West Asia & Europe”
” We present an integrative genetic history of the Southern Arc, an area divided geographically between West Asia and Europe, but which we define as spanning the culturally entangled regions of Anatolia and its neighbors, ‘in both Europe (Aegean and the Balkans), and in West Asia (Cyprus, Armenia, the Levant, Iraq and Iran). We employ a new analytical framework to analyze genome-wide data at the individual level from a total of 1,320 ancient individuals, 731 of which are newly reported and address major gaps in the archaeogenetic record. We report the first ancient DNA from the world’s earliest farming cultures of southeastern Anatolia and northern Mesopotamia, as well as the first Neolithic period data from Cyprus and Armenia, and discover that it was admixture of Natufian-related ancestry from the Levant—mediated by Mesopotamian and Levantine farmers, and marked by at least two expansions associated with dispersal of pre-pottery and pottery cultures—that generated a pan-West Asian Neolithic continuum. Our comprehensive sampling shows that Anatolia received hardly any genetic input from Europe or the Eurasian steppe from the Chalcolithic to the Iron Age; this contrasts with Southeastern Europe and Armenia that were impacted by major gene flow from Yamnaya steppe pastoralists.
In the Balkans, we reveal a patchwork of Bronze Age populations with diverse proportions of steppe ancestry in the aftermath of the ~3000 BCE Yamnaya migrations, paralleling the linguistic diversity of Paleo-Balkan speakers. We provide insights into the Mycenaean period of the Aegean by documenting variation in the proportion of steppe ancestry (including some individuals who lack it altogether), and finding no evidence for systematic differences in steppe ancestry among social strata, such as those of the elite buried at the Palace of Nestor in Pylos.
A striking signal of steppe migration into the Southern Arc is evident in Armenia and northwest Iran where admixture with Yamnaya patrilineal descendants occurred, coinciding with their 3rd millennium BCE displacement from the steppe itself. This ancestry, pervasive across numerous sites of Armenia of ~2000-600 BCE, was diluted during the ensuing centuries to only a third of its peak value, making no further western inroads from there into any part of Anatolia, including the geographically adjacent Lake Van center of the Iron Age Kingdom of Urartu. The impermeability of Anatolia to exogenous migration contrasts with our finding that the Yamnaya had two distinct gene flows, both from West Asia, suggesting that the Indo-Anatolian language family originated in the eastern wing of the Southern Arc and that the steppe served only as a secondary staging area of Indo-European language dispersal. The demographic significance of Anatolia on a Mediterranean-wide scale is further documented by our finding that following the Roman conquest, the Anatolian population remained stable and became the geographic source for much of the ancestry of Imperial Rome itself.“
OUR TAKE & PREDICTION
At Eurasian DNA we have been using short segment IBD analyses for the past 2 years for fine-scale work and it appears that Reich’s team is also starting to use it as well. We use short segment IBD analyses to distinguish more recent shared drift from more ancient shared genetic drift. For example, performing SNP by SNP comparison of two genomes such as used by many of the tools available to us will not necessarily tell us whether a West Eurasian individual shows a high genetic similarity to Yamnaya due to shared common ancestral components such as ENF, EHG, CHG, or whether this genetic similarity with Yamnaya is due to actual admixture from Yamnaya mediated via Steppe-MLBA and Steppe-IA populations.
Unfortunately over 95% of the available ancient DNA is a less accurate pseudo-haploid representation of the real thing which is unsuitable of IBD work. A few of the other issues we encounter that come to mind when we process the usual ancient DNA sequences is that the reads map to either multiple locations of the reference genome due to the reads being very short or wrong locations due to errors in the reads.
It’s difficult for us to do Identity by Descent (IBD) analyses using ancient human DNA because the overwhelming majority of the sequences out there don’t have enough read depth for us to produce the phased diploid genotypes we need perform IBD analyses.
Although here at Eurasian DNA we have been able produce accurate phased diploid genotypes from raw ancient DNA sequences for use in short IBD analyses, we have been limited to just a few since over 95% of the available ancient DNA does not make our quality control cutoff of 8X average read depth to enable accurate phased diploid genotyping.
It appears that Reich’s team have genotyped hundreds of new samples from Turkey. Iraq, Armenian, Iran, and surrounding areas and have been able to obtain a decent amount of higher quality ancient DNA from those regions to enable phased diploid genotyping and thus to determine negligible Steppe admixture into Anatolia from the Chalcolithic through the Iron Age. The implication here is if Indo-European languages did not come to Anatolia from the Steppe then the original staging ground for Proto-Indo-European languages and thus Yamnaya’s ancestors must have been near Anatolia ( likely Kurdistan and surrounds in NW Iran ). Additionally, Yamnaya’s predominant paternal ancestral haplogroup appears to be R-M269. This haplogroup is also found with high frequency in the eastern Turkey region. Thus if this region did not receive much steppe admixture, it’s likely this region had R-M269 prior to the formation of Yamnaya which would be consistent with this region being paternally ancestral to Yamnaya.
From here Yamnaya’s ancestors migrated to the Eurasian Steppe where they hybridized with descendants of EHG and formed the Yamnaya and the secondary staging area for the dispersal of Indo-European languages.
Subsequently some descendants of Yamnaya returned to Armenia and NW Iran, however that admixture would subsequently be diluted to 30% of its original value due to introgression of Anatolian admixture into Western Iran and Armenia.
Interestingly, we predicted this type of scenario 5 years ago when we performed in depth analysis of Eurasian Steppe admixture in present day Kurds. We were also one of the first to discover the genetic impact of the Iron Age steppe nomads on the demography of Kurds and other Indo-Iranians.
We are also hopeful that Reich’s team will make available higher coverage genomes from the Mede and perhaps Parthian periods. It seems that there will also be 3 new papers published covering the Neolithic to the Bronze Age
Link:
https://eurasiandna.com/lecture-by-...uthern-arc-a-bridge-between-west-asia-europe/