A recent study sequenced three hunter-gatherer genomes from Georgia and one from Switzerland, expanding our understanding of the pre-Neolithic genetic landscape of West Eurasia.
Eppie R. Jones et al., Upper Palaeolithic genomes reveal deep roots of modern Eurasians. Nature Communications 2015. Open access → LINK [doi:10.1038/ncomms9912]
We extend the scope of European palaeogenomics by sequencing the genomes of Late Upper Palaeolithic (13,300 years old, 1.4-fold coverage) and Mesolithic (9,700 years old, 15.4-fold) males from western Georgia in the Caucasus and a Late Upper Palaeolithic (13,700 years old, 9.5-fold) male from Switzerland. While we detect Late Palaeolithic–Mesolithic genomic continuity in both regions, we find that Caucasus hunter-gatherers (CHG) belong to a distinct ancient clade that split from western hunter-gatherers ~45 kya, shortly after the expansion of anatomically modern humans into Europe and from the ancestors of Neolithic farmers ~25 kya, around the Last Glacial Maximum. CHG genomes significantly contributed to the Yamnaya steppe herders who migrated into Europe ~3,000 BC, supporting a formative Caucasus influence on this important Early Bronze age culture. CHG left their imprint on modern populations from the Caucasus and also central and south Asia possibly marking the arrival of Indo-Aryan languages.
Figure 1: Genetic structure of ancient Europe.(a). Principal component analysis. Ancient data from Bichon, Kotias and Satsurblia genomes were projected11 onto the first two principal components defined by selected Eurasians from the Human Origins data set1. The percentage of variance explained by each component accompanies the titles of the axes. For context we included data from published Eurasian ancient genomes sampled from the Late Pleistocene and Holocene where at least 200 000 SNPs were called1, 2, 3, 4, 5, 6, 7, 9 (Supplementary Table 1). Among ancients, the early farmer and western hunter-gatherer (including Bichon) clusters are clearly identifiable, and the influence of ancient north Eurasians is discernible in the separation of eastern hunter-gatherers and the Upper Palaeolithic Siberian sample MA1. The two Caucasus hunter-gatherers occupy a distinct region of the plot suggesting a Eurasian lineage distinct from previously described ancestral components. The Yamnaya are located in an intermediate position between CHG and EHG. (b). ADMIXTURE ancestry components12 for ancient genomes (K=17) showing a CHG component (Kotias, Satsurblia) which also segregates in in the Yamnaya and later European populations.
The Swiss one (Bichon, Jura) is maybe less of a novelty, roughly falling within the already known parameters for Western European hunter-gatherers of Magdalenian tradition (WHG in the jargon) but the three samples from the Caucasus (CHG) are really a much needed new data-point, different from everything else that what we knew and surprisingly close to modern Caucasus populations.
They are however very distant from all other known ancient West Eurasian samples. Fig. 2 shows an estimated divergence with early Neolithic Europeans (EEF, Stuttgart) dating from before the Last Glacial Maximum, to 24,000 years ago. The divergence of this composite West Asian macro-population (EEF's Paleoeuropean admixture is accounted for separately) with the pre-Neolithic Europeans seems to be of c. 46,000 years, what is consistent with early Upper Paleolithic (the large error margin allows for a secondary Gravettian genesis contact anyhow). On the other hand the divergence between Bichon and Lochsbour seems to fit with the Magdalenian time-frame as one would expect.
CHG are surprisingly close to modern Caucasus population, particularly to Georgians. CHG also appear to be an excellent candidate population for the formation of the early Indoeuropean Yamna people, which fit best as a mix of CHG and EHG (Eastern European hunter-gatherers).
I find notable that the CHG component (do not confuse with the African one of similar color) is still apparent in the Indian subcontinent, something that was already detected in other analyses. The CHG component seems to be the core of the so called "ancient North Indian" (ANI) component, also known as "Gedrosian" or "Caucaso-Baloch". What they call in the above analysis "South Asian" would be approximately the also known as "ancient South Indian" (ASI) component, which is presumably pre-Neolithic.
"Farmer" means European Early Farmer (EEF) and already implies some Paleolithic European admixture, until we have some Levant and Mesopotamian genuine first Neolithic samples, we should not assume that all the Fertile Crescent Neolithic people were just like that, although some may have been close. In fact, I tend to think that the CHG or a similar "highlander" component was probably important in the Zagros Neolithic and consequently in the Mesopotamian and Iranian one, reaching eventually to South Asia. See here for more details on how the Neolithic expansion in Europe and India were largely parallel but not identical at all in source populations.
To illustrate this early Neolithic complexity, still apparent to some extent in West Asian genetics and, as I just said, in European and South Asian ones, the following archaeo-cultural map should help:
|Source: Eleni Asouti 2006 (red color annotation is mine)|
I strongly recommend to read the full source study, because it is very informative about what were some of our ancestors¹ doing when farming and herding were being developed in West Asia, but the map above alone gives a very good glimpse of the ethno-cultural complexity of these ancient West Asian populations.
My understading is that the mainline (Thessalian or Aegean) European Neolithic founders must have originated within the PPNA/B complex, although uncertain about which specific culture within it (most likely not Harifian because that one is surely at the origin of Semitic languages but almost any other one would do, notably those close to the Mediterranean coast: Sultanian, Aswadian and Mureybetian). Instead the populations affecting Eastern European, Mesopotamian-Iranian (Sumer and Elam) and Indian Neolithic are most probably rather linked to what is here called as M'lafatian or Zagros Neolithic, which in turn were most likely linked one way or the other to Caucasus hunter-gatherers and in general to the "highlander" West Asian element apparent in other studies in contrast to a more EEF-like "lowlander" one.
¹ Sure: I'm thinking mostly of Euro-Mediterranean and Central-South Asian peoples but even if you are East Asian or Tropical African it's still very probable that some random ancestor comes from this crucial paleo-historical knot (or almost from anywhere else: admixture never ends and we are all related, even if thinly, within the last millennium or so).