# Caucasus hunter-gatherer

Caucasus hunter-gatherer (CHG), also called Satsurblia cluster, is an anatomically modern human genetic lineage, first identified in a 2015 study, based on the population genetics of several modern Western Eurasian (European, Caucasian and Near Eastern) populations.
It represents an ancestry maximised in some Upper Paleolithic and Mesolithic hunter-gatherer groups in the Caucasus. These groups are also very closely related to Mesolithic hunter-gatherers and Neolithic farmers in the Iranian Plateau, who are sometimes included within the CHG group. Ancestry that is closely related to CHG-Iranian Neolithic farmers is also known from further east, including from the Bactria–Margiana Archaeological Complex and the Harappan/Indus Valley Civilisation. Caucasus hunter-gatherers and Eastern hunter-gatherers are ancestral in roughly equal proportions to the Western Steppe Herders (WSH), who were widely spread across Europe and Asia beginning during the Chalcolithic.

## Formation and development

The CHG lineage is suggested to have diverged from the ancestor of Western Hunter-Gatherers (WHGs) probably during the Last Glacial Maximum (sometime between 45,000 to 26,000 years ago). They further separated from the Anatolian hunter-gatherer (AHG) lineage later, suggested to around 25,000 years ago during the late LGM period. The Caucasus hunter-gatherers managed to survive in isolation since the late LGM period as a distinct population, and display high genetic affinities to Mesolithic and Neolithic populations on the Iranian plateau, such as Neolithic specimens found in Ganj Dareh. The CHG display higher genetic affinities to European and Anatolian groups than Iranian hunter-gatherers do, suggesting a possible cline and geneflow into the CHG and less into Mesolithic and Neolithic Iranian groups.
According to one model, the Mesolithic/Neolithic Iranian lineage basal to the Caucasus hunter-gatherers are inferred to derive significant amounts of their ancestry from Basal Eurasian (c. 38–48%), with the remainder ancestry being closer to Ancient North Eurasians or Eastern European Hunter-Gatherer (ANE/EHG; c. 52–62%). The CHG displayed an additional ANE-like component (c. 10%) than the Neolithic Iranians do, suggesting they may have stood in continuous contact with Eastern Hunter-Gatherers to their North. The CHG also carry around 20% additional Paleolithic Caucasus/Anatolian ancestry. Lazaridis et al. (2016) models the CHG as a mixture of Neolithic Iranians, Western Hunter-Gatherers and Eastern Hunter-Gatherers. In addition, CHG cluster with early Iranian farmers, who significantly do not share alleles with early Levantine farmers.
An alternative model without the need of significant amounts of ANE ancestry has been presented by Vallini et al. (2024), suggesting that the initial Iranian hunter-gatherer-like population which is basal to the CHG formed primarily from a deep Ancient West Eurasian lineage ('WEC2', c. 72%), and from varying degrees of Ancient East Eurasian (c. 10%) and Basal Eurasian (c. 18%) components. The Ancient West Eurasian component associated with Iranian hunter-gatherers (WEC2) is inferred to have diverged from the West Eurasian Core lineage (represented by Kostenki-14; WEC), with the WEC2 component staying in the region of the Iranian Plateau, while the proper WEC component expanded into Europe.
Irving-Pease et al. (2024) models CHG as being derived from an Out of Africa population that split into basal Northern Europeans and West Asians. The latter was where CHG originated from.
At the beginning of the Neolithic, at c. 8000 BC, they were probably distributed across western Iran and the Caucasus, and people similar to northern Caucasus and Iranian plateau hunter-gatherers arrived before 6000 BC in Pakistan and north-west India. A roughly equal merger between the CHG and Eastern Hunter-Gatherers in the Pontic–Caspian steppe resulted in the formation of the Western Steppe Herders (WSHs). The WSHs formed the Yamnaya culture and subsequently expanded massively throughout Europe during the Late Neolithic and Early Bronze Age c. 3000—2000 BC.
Caucasus hunter gatherer/Iranian-like ancestry, was first reported as maximized in hunter-gatherers from the South Caucasus and early herders/farmers in northwestern Iran, particularly the Zagros, hence the label "CHG/Iranian”.

### Further research

Jones et al. (2015) analyzed genomes from males from western Georgia, in the Caucasus, from the Late Upper Palaeolithic (13,300 years old) and the Mesolithic (9,700 years old). These two males carried Y-DNA haplogroup: J* and J2a, later refined to J1-FT34521, and J2-Y12379*, and mitochondrial haplogroups of K3 and H13c, respectively. 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.
CHG ancestry was also found in an Upper Palaeolithic specimen from Satsurblia cave (dated c. 11000 BC), and in a Mesolithic one from Kotias Klde cave, in western Georgia (dated c. 7700 BC). The Satsurblia individual is closest to modern populations from the South Caucasus.
Margaryan et al. (2017) analysing South Caucasian ancient mitochondrial DNA found a rapid increase of the population at the end of the Last Glacial Maximum, about 18,000 years ago. The same study also found continuity in descent in the maternal line for 8,000 years.
According to Narasimhan et al. (2019) Iranian farmer related people arrived before 6000 BCE in Pakistan and north-west India, before the advent of farming in northern India. They suggest the possibility that this "Iranian farmer–related ancestry [...] was [also] characteristic of northern Caucasus and Iranian plateau hunter-gatherers."

## Proto-Indo Europeans

During the Neolithic and early Eneolithic, likely during the 4th millennium BC, Caucasus hunter-gatherers (CHGs) mixed with Eastern Hunter-gatherers (EHGs) on the Pontic–Caspian steppe, with the resulting population, almost half-EHG and half-CHG, forming the genetic cluster known as Western Steppe Herder (WSH). To David W. Anthony, Caucasus hunter-gatherer ancestry of Yamnaya is often with higher than 50%. As well as an overwhelming WSH ancestry, Yamnaya also have additional admixture from Anatolian and Levantine farmers, and the Western Hunter-gatherers (WHGs).
According to co-author Andrea Manica of the University of Cambridge:
   The question of where the Yamnaya come from has been something of a mystery up to now […] we can now answer that, as we've found that their genetic make-up is a mix of Eastern European hunter-gatherers and a population from this pocket of Caucasus hunter-gatherers who weathered much of the last Ice Age in apparent isolation.
Some scholars argue that the archaic PIE ('Indo-Anatolian') language may have originated among a CHG-rich population in Western Asia, based on the lack of EHG ancestry in the probable speakers of Anatolian languages. Others, such as Anthony, suggest that PIE was spoken by EHGs living in Eastern Europe.
According to Jones et al. (2015), Caucasus hunter-gatherer (CHG) "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 correlating with the arrival of Indo-Aryan languages." For example, about 50–70% of Armenian ancestry is derived from CHG, persisting from Neolithic times to the present. Wang et al. (2018) 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". According to Allentoft et al. (2024), The arrival and admixture of CHG with Caspian steppe cultures is dated to about 7,300-years-old, which is seen in two ancient samples from Golubaya Krinitsa with 18–24% admixture.

## Ancient Greece, Aegean and Italy

Beyond contributing to the population of mainland Europe through Bronze Age pastoralists of the Yamnaya, CHG also appears to have arrived on its own in the Aegean without Eastern European hunter–gatherer (EHG) ancestry and provided approximately 9–32% of ancestry to the Minoans. The origin of this CHG component might have been Central Anatolia.
Genetic analysis shows that Iranian-related ancestry, which was widespread in the Aegean by the Middle Bronze Age in association with the Minoan and Mycenaean cultures, had also spread as far west as Sicily in substantial proportion at least by the time of the Mycenaeans. One possibility is this ancestry spread west along with the Mycenaean cultural expansion. An arrival of the CHG-related component in Southern Italy from the Southern part of the Balkan Peninsula, including the Peloponnese, is compatible with the identification of genetic corridors linking the two regions and the presence of Southern European ancient signatures in Italy. Collected data from Iron Age individuals dating from 900 to 200 BCE (including the Republican period) group shows a clear ancestry shift from the Copper Age, interpreted by ADMIXTURE as the addition of a Steppe-related ancestry component, and an increase in the Neolithic-Iranian component.

## Central Asia and South Asia

CHG/Iranian Plateau Neolithic-like ancestry is prominent in pre-steppe admixture Chalcolithic and Bronze Age (4500–2000 BCE) populations in Central Asia, like the Bactria–Margiana Archaeological Complex (which also had Anatolian Neolithic Farmer-related ancestry) as well as in the northwestern Indian subcontinent such as in sites in or adjacent to the Indus Valley Civilisation (who have mixed CHG-related and Ancient Ancestral South Indian ancestry). It is unclear as to whether the dispersal of CHG/Iranian Plateau-related ancestry eastwards to the Indian subcontinent was the result of the migration of farmers or an earlier dispersal of hunter-gatherers who later adopted farming, but this dispersal likely occurred sometime before 6000 BCE due to the lack of Anatolian Farmer-related ancestry in ancient South Asians, but which is present in the Iranian Plateau after this time. This pre-steppe CHG-related ancestry makes up a significant proportion of the ancestry of modern South Asians. WSHs, who were of significant CHG ancestry, also later migrated into Central Asia and South Asia.