Age: 60KYA to 40KYA (Initial Upper Palaeolithic) |
Associated Populations: Basal Eurasians, Early Wave HGs, East Eurasian Core, West Eurasian Core |
Associated Cultures: N/A (theoretical population) |
Associated Maternal Haplogroups: N/A (theoretical population) |
Associated Sites: N/A (theoretical population) |
Associated Paternal Haplogroups: N/A (theoretical population) |
Homo sapiens began to migrate from Africa into Eurasia around 70-60KYA. However, a widespread and stable expansion throughout all of Eurasia did not happen until about 45KYA. As shown in this article, there were multiple migrations out of Africa, though the initial migrations did not affect Eurasia genetically. A temporal gap of approximately 20 thousand years existed between initial migrations out of Africa and the stable colonization of Eurasia. The Eurasian population formed after migrations out of Africa and before the stable colonization of Eurasia can be characterized as a hub population from which multiple populations, which later colonized Eurasia, were derived. This hub most likely was located in the Iranian Plateau, being occupied from 60 to 40KYA. Upper Palaeolithic technological complexes in the region appeared relatively quickly, indicating a widespread replacement of earlier populations.1
It has already been established that there was a phylogenetic split between Basal Eurasians, East Eurasians, and West Eurasians, with Basal Eurasians representing an earlier Out of Africa lineage.2 Additionally, the existence of a population hub from which all non-African populations originated has already been posited.3 However, in the absence of fossil evidence, genetic evidence was utilized by Vallini, L., Zampieri, C., Shoaee, M.J. et al. (2024) to infer the geographic source from which Out of Africa populations diverged. Utilizing derived allele sharing with respect to the oldest (and unadmixed) representatives of the East Eurasian and West Eurasian Cores, the Tianyuan Man and Kostenki14 respectively (link WEC specifically to Kostenki), a visual framework was established with derived allele sharing with one individual representing the x axis and the other representing the y axis. Given that other ancient Eurasian individuals would fall somewhere on either axis in a way that is representative to the evolutionary time spent with either population. Theoretically, a population that falls where the two axes intersect would be representative of the hub population that phylogenetically represents the point at which the East and West Eurasian Cores split, though there are various confounders, such as admixture, that may influence a population's position on such a plot. Given patterns of shared drift, a relic hub population would be identified among populations possessing a West Eurasian genetic signature while having the least shared drift with West Eurasian Core-associated populations. Accounting for confounders, the population that possesses a West Eurasian Core component closest to the hub population possess Neolithic Iranian ancestry.4 Additionally, from a genetic perspective, a focal area was established to cover much of the Iranian Plateau and parts of the Arabian Peninsula.5 Additionally, by using this method to establish a potential point of entry for Basal Eurasian ancestry, the Arabian Peninsula, the Levant, and North Africa can be ruled out as hub locations given the need for geographical distinction between the hub and where Basal Eurasians resided.6 Additionally, environmental analyses support the hypothesis of the Iranian Plateau as a hub population due to its optimal climate and carrying capacity compared to other regions.7
The Iranian Plateau was able to support human occupation from 70 to 30KYA, potentially being able to support a larger population size than other regions in West Asia. However, there was a period from 60 to 50KYA in which the Iranian Plateau became less habitable, with the carrying capacity decreasing before increasing once again after this period ended. The ecological changes causing this (relative to the other time spans mentioned) brief decrease in carrying capacity could have served as an impetus for pre-45KYA expansions into Eurasia during the Initial Upper Palaeolithic.8
According to the topologies posited in the paper that presented the Iranian Hub theory, the Basal Eurasian lineage was the first population related to the hub population to diverge, with the Basal Eurasian and Hub lineages representing a bifurcation of the Out of Africa lineage.9 Subsequent migrations into the rest of Eurasia likely occurred nearly concurrently with respect to the population related to Ust'-Ishim and the East Eurasian Core, forming a near trifurcation of the phylogeny of the Hub-derived populations,10 with one branch representing the population related to Ust'-Ishim, one related to the East Eurasian Core, and one related to the West Eurasian Core, albeit with Ust'-Ishim's branch potentially splitting before the branch representing the East Eurasian Core.11 A previous paper delineating the existence of a population hub places Ust'-Ishim as a population descending from the early East Eurasian Core.12 Such a phylogenetic placement outlines that Ust'-Ishim has shared affinity with East Eurasian Core populations, yet split at a period temporally very close to the split of the East and West Eurasian Cores. Given that the paper primarily discussed in this article outlines a differentiation between the genetic signature of a theoretical hub population before and after migrations associated with the East Eurasian Core (as the EEC migration occurred before the WEC migration), Ust'-Ishim's phylogenetic affinity to the East Eurasian Core could be explained temporally, as Ust'-Ishim's branch and the East Eurasian Core's branch potentially developed concurrently.
As implied in the previous paragraph, expansions beginning around 45KYA, associated with the Initial Upper Palaeolithic, likely represented a migration of the East Eurasian core from the hub, leaving descendants throughout Eurasia but only significantly impacting the genetic landscape of East Eurasian populations. Beginning around 38KYA, migrations of the West Eurasian Core population from the hub into Eurasia ultimately replaced pre-45KYA migrations into the continent.13
Sources
1, 4, 5, 6, 7, 8, 10, 13 Vallini, L., Zampieri, C., Shoaee, M.J. et al. The Persian plateau served as hub for Homo sapiens after the main out of Africa dispersal. Nat Commun 15, 1882 (2024). https://doi.org/10.1038/s41467-024-46161-7