Iranian hunter-gatherers

Not to be confused with Indo-Iranians or Iranian peoples.

The term Iranian hunter-gatherers or Neolithic Iranians, sometimes also "East Meta", is used to refer to a population genomics lineage representing the Mesolithic to early Neolithic population of the Iranian plateau, South-Central Asia and the Caucasus.^[1]

The Iranian hunter-gatherer lineage is represented by Mesolithic hunter-gatherers and later Neolithic herders and early farmers in present-day Iran, such as remains excavated from the Hotu and Kamarband Caves and Ganj Dareh, as well as Wezmeh. A deeply diverged sister branch (> 12kya) best represented by remains from Shahr-i-Sokhta, formed the dominant ancestry component of the Indus Valley Civilisation in Northwestern India, which was mixed with a local East Eurasian component termed Ancient Ancestral South Indian (AASI). The Iranian hunter-gatherers also represent an important source for the formation of the Central Asian gene pool, primarily via the Bactria–Margiana Archaeological Complex. They further displayed close genetic affinities to the Caucasus hunter-gatherers, who descend primarily from a similar source population as Iranian hunter-gatherers, but were distinct from preceding Paleolithic Caucasus populations, which were closer related to Anatolian hunter-gatherers, Western hunter-gatherers and Levantine groups.

Origins

One possible admixture graph (Allentoft et al. 2024) of deep Eurasian lineages in context of modern West Eurasians.^[2]

Principal Components Analysis of Ancient West Eurasians: Eigenvectors were inferred using present-day populations (gray points) and the ancient samples (colored shapes) were projected onto the plot.

Iranian-hunter gatherers are inferred to have originated from the local Upper Paleolithic population of the Persian plateau. The Persian plateau acted as population hub during the initial colonisation of Eurasia after the Out-of-Africa expansion of modern humans (between 70–46kya). The region is also close to the area which may have harbored the Basal Eurasian lineage, which is supposed to have been centered in the now sunken Persian Gulf, and which displayed no or significantly reduced archaic admixture.^[1][3][4][5]

While Iranian hunter-gatherers are broadly placed as part of the wider "West Eurasian" cluster, the exact origin of the Mesolithic and Neolithic Iranian hunter-gatherers and later farmers remains unclear. Mesolithic hunter-gatherer remains from the Alborz mountain range were found to show ancestry primarily related to Basal Eurasians (c. 48–66%), and are ancestral to later Neolithic herders and farmers.^{[4][6][7][8][9][5]}

The later Neolithic Iranians are commonly modeled as two-way admixture between a Basal Eurasian-rich lineage and a lineage closer to Ancient North Eurasians (ANE) or Eastern European Hunter-Gatherers (EHG). Accordingly, the Mesolithic/Neolithic Iranian lineage derives the majority of their ancestry from a local Basal-rich source (ranging from 48–68%), with the remainder ancestry being closer to Ancient North Eurasians (32–52%).^{[10][6][11][2][5][12]}

Mesolithic and Neolithic Iranians fall along a cline between inferred Basal Eurasian and ANE/EHG-related ancestries. This stands in contrast to Neolithic Anatolian and Levant groups, who fall along a cline between Basal Eurasian and WHG-related ancestries. Natufians, despite sharing most of their ancestry with Neolithic Anatolian groups, have an additional "Ancient North African" (ANA) ancestry component.^[5][6] This distinction is also evident in that Iranian hunter-gatherers and Neolithic Iranian groups are taking up an "extreme position" compared against other ancient and modern West Eurasian populations within an Eurasian-wide Principal component analysis (PCA).^{[13][14][6][5]}

The f4-ratio estimation for the total amount of Basal Eurasian ancestry stands in correlation with the reduced archaic allele sharing among Iranian hunter-gatherers and later herders or early farmers.^[6] Yet alternative explanations, such as purifying selection, may affect the amount of archaic alleles independently from Basal Eurasian admixture.^[15]

Alternatively, Neolithic Iranians can also be modeled via either a three-way admixture, including a primarily (c. 53%) Upper Paleolithic Caucasus/Dzudzuana-like source (itself an admixture between c. 24–28% Basal Eurasian and c. 72–76% Upper Paleolithic European ancestry; and close to later Anatolian hunter-gatherers), and variable amounts of geneflow from an ANE-like source (21%), and an additional Basal Eurasian source (26%); or a four-way admixture with approximately 53–62% Upper Paleolithic Caucasus/Dzudzuana-like ancestry, 16–22% ANE-like ancestry, 10–13% Onge-like ancestry, and 9–15% additional Basal Eurasian-like ancestry.^[13][16][5]

Vallini et al. (2024) argued that Mesolithic/Neolithic Iranians carry in part a deeply diverged West Eurasian ancestry (WEC2) which stayed closer to the inferred population hub on the Persian plateau than compared to Upper Paleolithic Europeans (WEC or Kostenki-14). This deeply diverged West Eurasian component, after contact events with nearby populations, including Basal and East Eurasian ancestries, resurfaced in the palaeogenetic record as the Iranian Neolithic, the Iranian Hunter Gatherer’ or the "East Meta". A qpAdm model by Vallini et al. 2024, including the simulated proxies for the WEC/WEC2 as well as Basal/BEA componets (Gumuz as proxy for BEA), the genetic makeup of Neolithic Iranians (Ganj_Dareh_N) consists of c. 76.5% West Eurasian (WEC/WEC2), c. 16.3% broadly East Eurasian (EEC), and c. 7.2% "Basal-like" (BEA) ancestries.^[1]

While initially absent from Anatolia, Mesopotamia and the Caucasus, as well as India, it reached these regions via the expansion of Mesolithic and Neolithic groups, resulting in a cline between Iran Neolithic-like and local sources.^[5]

Uniparental haplogroups

Hotu cave dwellers in Alborz mountain range were identified as Iranian hunter gatherer

Ganj Dareh herders were of Iranian hunter gatherer ancestry

The main human Y-chromosome DNA haplogroups found among Mesolithic and Neolithic Iranian-affiliated specimens include subclades of G, J, L, and R2, while subclades of H are observed among 'IVC periphery' like remains. Others included subclades of T. The oldest sample of haplogroup R2a to date has been found in one of the remains from Ganj Dareh in western Iran. Common Human mitochondrial DNA haplogroups found among Mesolithic and Neolithic Iranian specimens include subclades of haplogroup U, HV, X, R, H, W, T, and M.^{[17][7][18][5]}

Contributions to other populations

Caucasus

Caucasus hunter-gatherers were found to be distinct from the earlier Upper Paleolithic Caucasus/Dzudzuana population, but closely related to Mesolithic and Neolithic Iranians. They are inferred to descend primarily from the same source population, which reached the Caucasus region sometimes betwee 25kya and 13kya. They can be used as interchangeable source for Holocene populations, with various names have been created to group them together, such as Iran_N/CHG, Iran/Caucasus or Zagros/Caucasus ancestry.^[19][1] The CHG can be modeled as merger between an Iranian hunter-gatherer related source (c. 72%), an UP Caucasus (Dzudzuana) related source (c. 18%), and an Eastern hunter-gatherer related source (c. 10%).^[20][2] An alternative model suggests c. 72% from an Iranian hunter-gatherer source, c. 21% from an EHG-like source, and c. 7% from a WHG-like source.^[6]

West Asia

The later Chalcolithic Iranians are modeled to have formed from a merger of local Neolithic Iranians and a Neolithic Levantin-like source population, as well as additional Caucasus hunter-gatherer-like geneflow. Chalcolithic Iranians can be modeled to derive c. 80% of their ancestry from a Neolithic Iranian-like group and c. 20% from a Neolithic Levantine-like group (which itself carried Neolithic Anatolian and Natufian components). Alternatively, they can be modeled as two-way admixture between c. 87% CHG-like and 13% Neolithic Levantine-like, or as three-way admixture between c. 17% Iranian hunter-gatherers, 63% CHG-like, and 20% Neolithic Levantine-like.^[6][21]

During the Late Neolithic/Early Chalcolithic period they formed a cline stretching from Western Anatolia along the lowlands of the Southern Caucasus to the Zagros mountains, reaching as far as to Southern Central Asia, as well as southwards to the Southern Levant. This cline was primarily characterized by expansive Anatolian and Iranian-like ancestries and secondarily by the spread of Levantine-like ancestry.^[22] Chalcolithic Iranian groups had a wide impact on Chalcolithic Anatolians and Bronze Age Levantine groups, contributing 33% and 44% ancestry respectively.^[6]

A Neolithic Iranian-like contribution is needed in models for modern Middle Eastern and certain Eastern African populations. This geneflow may have happened primarily via an admixed population from the Mesopotamia.^[23]

South Asia

An Ancient Harappan Genome

In 2019, the genome sequence of a skeleton remain from a cemetery near Rakhigarhi dating to around 2,800-2,300 BCE, suggesting that the majority of the genome was related to Iranian hunter-gatherers. The divergent (>12kya) sister lineage, sharing a recent common ancestor with Neolithic Iranians, but having diverged from them prior to the development of agriculture, best represented by remains from Shahr-i-Sokhta, forms the main ancestry component of the Indus Valley Civilisation, in tandem with variable amounts of a local East Eurasian ancestry termed Ancient Ancestral South Indian (AASI). The spread of Ancient Iranian-like ancestry, and or IVC-like ancestry, may be related to the dispersal of early Dravidian languages, although this remains uncertain, with opposing views having been presented as well, with some scholars connecting this ancestry with the spread of Indo-Aryan languages.^{[24][8][7][12][25][26][27][28]}

Central Asia

Neolithic Iranians, in tandem with Anatolian Farmers, also contributed to the formation of the Bactria–Margiana Archaeological Complex (BMAC), which subsequently contributed to other Central Asian populations, and possibly later Tarim mummies from Alwighul (700–1 BCE) and Krorän (200 CE).^[24][7][29] The BMAC population is inferred to have formed primarily from Iran_N (60–65%) and Anatolia_N (20–25%) ancestries, with the remainder (~10%) being derived from a West Siberian HG-like source (WSHG).^[30][31][7]

Europe

Neolithic Iranians, in contrast to the related Caucasus hunter-gatherers, only made minor contributions to the European gene pool.^[24] Neolithic Iranians instead represent a better source of geneflow among most West Asian populations when compared against Caucasus hunter-gatherers, while the contrary is true for European populations.^[32]

See also

• History of Iran
• Peopling of India
• Genetics and archaeogenetics of South Asia
• Genetic history of the Middle East