Caucasus Hunter-Gatherer


Caucasus hunter-gatherer, also called Satsurblia Cluster is the name of an anatomically modern human genetic lineage, first identified in a 2015 study, based on the population genetics of several modern Western Eurasian populations.
CHG ancestry was also found in an Upper Palaeolithic specimen from Satsurblia cave, and in a Mesolithic one from Kotias Klde cave, in western Georgia.
The CHG lineage descended from a population that split off the base Western Eurasian lineage very early, around 45,000 years ago, pre-dating the split that led to differentiated populations that descended separately to Ust'-Ishim man, Oase1 and European hunter-gatherers. The Caucasus hunter-gatherers managed to survive in isolation through the Last Glacial Maximum as a distinct population.
Eastern Hunter-Gatherers are believed to have received admixture from CHGs, leading to the formation of Western Steppe Herders. WSHs formed the Yamnaya culture and expanded massively throughout Europe during the Late Neolithic and Early Bronze Age.
The 2015 study by Jones et al. analysed "Eurasian steppe ancestry" – which is associated with the Ancient North Eurasian lineage – among modern European populations, which is linked to the Indo-European expansion. In comparison to modern human populations, the Satsurblia individual is closest to modern populations from the South Caucasus.

Genetic studies

The study detected a split between CHG and so-called "Western European Hunter-Gatherer" lineages, about 45,000 years ago, the presumed time of the original peopling of Europe. CHG separated from the "Early Anatolian Farmers" lineage later, at 25,000 years ago, during the Last Glacial Maximum. and the other 9,700 years, which were compared to the 13,700 year-old Bichon man genome.
Jones et al. analyzed genomes from males from western Georgia, in the Caucasus, from the Late Upper Palaeolithic and the Mesolithic. These two males carried Y-DNA haplogroup: J* and J2a, later refined to J1-Y6305*, and J2-Y12379*, and mitochondrial haplogroups of K3 and H13c, respectively. The researchers found that these Caucasus hunters were probably the source of the Near Eastern DNA in the Yamnaya. Their genomes showed that a continued mixture of the Caucasians with Middle Eastern populations took place up to 25,000 years ago, when the coldest period in the last Ice Age started.
Yardumian et al. in a population genetics study on the Svans of northwestern Georgia found significant heterogeneity in mt-DNA, with common haplogroups including U1‐U7, H, K, and W6, while Y-DNA haplogroups were less diverse, 78% of Svan males being bearers of Y-haplogroup G2a. Wang et al. analysed genetic data of the North Caucasus of fossils dated between the 4th and 1st millennia BC and found correlation with modern groups of the South Caucasus, concluding that "unlike today - the Caucasus acted as a bridge rather than an insurmountable barrier to human movement".
Lazaridis et al. proposes a different people, likely from Iran, as the source for the Middle Eastern ancestry of the Yamnaya people, finding that "a population related to the people of the Iran Chalcolithic contributed ~43% of the ancestry of early Bronze Age populations of the steppe". That study asserts that these Iranian Chalcolithic people were a mixture of "the Neolithic people of western Iran, the Levant, and Caucasus Hunter Gatherers". The Near East population were most likely hunter-gatherers from the Caucasus, though one study suggested that farmers dated to the Chalcolithic era from what is now Iran may be a better fit for the Yamanya's Near Eastern descent. A different analysis, carried out by Gallego-Llorente et al., concludes that Iranian populations are not a likelier source of the 'southern' component in the Yamnaya than Caucasus hunter-gatherers.

Proto-Indo Europeans

The CHG lineage was found to have contributed significantly to the Yamnaya lineage of Chalcolithic pastoralists in the Pontic steppe, which in turn expanded into Europe from about 5,000 years ago. CHG admixture was also found in South Asia, in a possible marker of the Indo-Aryan migration there.
The proto-Indo-Europeans, i.e. the Yamnaya people and the related cultures, seem to have been a mix from Eastern European Hunter-Gatherers ; and people related to the near east, such as Caucasus hunter-gatherers and Iran Chalcolithic people, with a Caucasian hunter-gatherer component. Each of those two populations contributed about half the Yamnaya DNA. According to co-author Andrea Manica of the University of Cambridge:
According to Jones et al., Caucasus hunter-gatherers "genomes significantly contributed to the Yamnaya steppe herders who migrated into Europe ~3,000 BCE, 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."

Chronology

There was probably a migration of populations from the Near East and Caucasus to Europe during the Mesolithic, around 14,000 years ago, much earlier than the migrations associated with the Neolithic Revolution. A few specimens from the Villabruna Cluster also show genetic affinities for East Asians that are derived from gene flow. The light skin pigmentation characteristic of modern Europeans is estimated to have spread across Europe in a "selective sweep" during the Mesolithic. The associated TYRP1 alleles, SLC24A5 and SLC45A2, emerge around 19,000 years ago – during the LGM and most likely in the Caucasus. The HERC2 variation for blue eyes first appears around 13,000 to 14,000 years ago in Italy and the Caucasus.
Caucasus Hunter Gatherers contributed to the formation of the Yamna culture, since Samara hunter-gatherers featured only Eastern European Hunter Gatherer ancestry and no CHG ancestry, whereas Yamna samples had up to 43% of CHG ancestry.
Margaryan et al. analysing South Caucasian ancient mitochondrial DNA found continuity in descent in the maternal line for 8,000 years. The same study also found a rapid increase of the population at the end of the Last Glacial Maximum, about 18,000 years ago. Modern Armenians were found to derive from an admixture event in the Bronze Age, which combined various Eurasian lineages. Since the time of the Bronze Age collapse, about 1200 BCE, Armenians have remained genetically isolated as a population, with a higher genetic affinity to Neolithic Anatolians, the Neolithic Levant, and Neolithic European farmers than to modern Near Eastern populations.