The term Iranian hunter-gatherers (IHG), is used to refer to a population genomics lineage representing the Mesolithic to early Neolithic population of the Iranian plateau, South Asia, South-Central Asia and the Caucasus.
The Iranian hunter-gatherer lineage is represented by Mesolithic hunter-gatherers and later by Neolithic herders and early farmers in present-day Iran, such as remains excavated from the Hotu and Kamarband Caves and Ganj Dareh, Tepe Abdul Hosein, as well as Wezmeh. A deeply diverged sister branch (at least 12,000 years BP), best represented by remains from Shahr-i-Sokhta BA2 individuals from Indus Periphery cline, 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). Later analyses detect an Anatolian farmer related signal in some of the Indus Periphery samples, likely mediated through early Neolithic or Copper Age Central Asian groups such as Sarazm and Namazga. This indicates that part of the Iran_N related ancestry in the Indus Periphery group was accompanied by Anatolian farmer input from West Asia with the spread of farming, rather than being exclusively pre-agricultural Iranian hunter-gatherer related.Kerdoncuff, E., Skov, L., Patterson, N., Zhao, W., Lueng, Y. Y., et al. (2024). "50,000 years of Evolutionary History of India: Insights from ~2,700 Whole Genome Sequences." bioRxiv2024.02.15.580575. https://doi.org/10.1101/2024.02.15.580575.Maier, R., Flegontov, P., Flegontova, O., Işıldak, U., Changmai, P., Reich, D., et al. (2023). "On the limits of fitting complex models of population history to f-statistics." eLife 12: e85492. https://doi.org/10.7554/eLife.85492. 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
Iranian hunter-gatherers are inferred to have originated from the local Upper Paleolithic population of the Iranian plateau. The Iranian 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.
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.
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%).
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. 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).
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. Yet alternative explanations, such as purifying selection, may affect the amount of archaic alleles independently from Basal Eurasian admixture.
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.
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 components (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/Gumuz) ancestries.
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.
Uniparental haplogroups The main human Y-chromosome DNA haplogroups found among Mesolithic and Neolithic Iranian-affiliated specimens include subclades of J, G, and R2, while subclades of L are observed among early divergent '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.
Contributions to other populations
Caucasus (Upper Paleolithic to Mesolithic) Caucasus hunter-gatherers were found to be distinct from the earlier Upper Paleolithic Caucasus/Dzudzuana population, but closely related to the Mesolithic and Neolithic Iranians. They are inferred to descend primarily from the same source population, which reached the Caucasus region sometimes between 13,000 to 25,000 years ago, during the Last Glacial Maximum or the beginning of the Bølling–Allerød Interstadial. 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. 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%). 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.
Upper Mesopotamia and the South Caucasus During the Early Holocene (9700–6200 BCE), genetic modelling cannot reliably distinguish Iran_N from CHG. Based on archaeological syntheses, the Iran_N gene pool spread westward from the northwest Zagros into Upper Mesopotamia and then into Central Anatolia, whereas contacts between the South Caucasus and the northern Fertile Crescent were only occasional in this interval.
Chataigner documents a clear east–west gradient in Iran_N proportions across the northern Fertile Crescent, with highest levels in the northwest Zagros (Shanidar, Bestansur at 75-80%), intermediate levels in the Upper/Middle Tigris (Nemrik 9, Boncuklu Tarla at 50-70%), and lower levels toward the Upper Tigris (Cayonu at 33%), the Middle Euphrates (Nevalı Çori at 15%), and Central Anatolia (between 0% to up to 30%), with negligible amounts in Western Anatolia and the Levant.
The westward diffusion is argued to have proceeded via small, mobile groups—including specialised craftsmen—moving from the northwest Zagros through Upper Mesopotamia toward the Taurus and Central Anatolia. By mid–Early Holocene, this Iran_N gene pool is variably present from the Zagros to Central Anatolia while peripheral regions remain less affected.