Basal Eurasian

Basal Eurasian is a proposed lineage of anatomically modern humans with reduced, or zero, Neanderthal admixture (ancestry) compared to other ancient non-Africans. Basal Eurasians represent a sister lineage to other Eurasians and may have originated from the Southern Middle East, specifically the Arabian Peninsula, or North Africa, and are said to have contributed ancestry to various West Eurasian, South Asian, and Central Asian as well as African groups. This Basal Eurasian component is also proposed to explain the lower archaic admixture among modern West Eurasians compared to with East Eurasians, although alternatives without the need of such Basal admixture exist as well.^[1] Basal Eurasian ancestry had likely admixed into West Eurasian groups present in West Asia as early as 26,000 years ago, prior to the Last Glacial Maximum, with this ancestry being subsequently spread by later migrations, such as those of the Anatolian Neolithic Farmers into Europe during the Holocene.^[2]

A study by Lazaridis et al. in 2014 demonstrated that modern Europeans can be modelled as an admixture of three ancestral populations; Ancient North Eurasians (ANE), Western Hunter-Gatherers (WHG), and Early European Farmers (EEF).^[3] This same study also showed that EEFs harbour ancestry from a hypothetical non-African 'ghost' population which the authors name 'Basal Eurasians'. This group, who have not yet been sampled from ancient remains, are thought to have diverged from all non-African populations c. 60,000 to 100,000 years ago, before non-Africans admixed with Neanderthals (c. 50,000 to 60,000 years ago) and diversified from each other. A second study by Lazaridis et al. in 2016 found that populations with higher levels of Basal Eurasian ancestry have lower levels of Neanderthal ancestry, which suggests that Basal Eurasians had lower levels of Neanderthal ancestry compared with other non-Africans. Another study by Ferreira et al. in 2021 suggested that Basal Eurasians diverged from other Eurasians between 50,000 and 60,000 years ago, and lived somewhere in the Arabian peninsula, specifically the Persian Gulf region, shortly before proper Eurasians admixed with a Neanderthal population in a region stretching from the Levant to northern Iran.^{[4][5][6][7][8]} Vallini et al. 2024 argues that the Basal Eurasian lineage diverged from other Eurasians soon after the Out-of-Africa migration, and subsequently became isolated, until it started to mix with other populations in the Middle East since around 25,000 years ago. These different Middle Eastern populations would later spread Basal Eurasian ancestry via the Neolithic Revolution to all of Western Eurasia.^[9]

In modern populations, Neanderthal ancestry is around 10% to 20% lower in West Eurasians than East Eurasians, with intermediate levels found in South and Central Asian populations. Although a scenario involving multiple admixture events between modern humans and Neanderthals is an alternative possibility, the most likely explanation for this is that Neanderthal ancestry in West Eurasians and South and Central Asians was diluted by admixture with Basal Eurasian groups.^[5]

The earliest evidence of Basal Eurasian ancestry is found in individuals from Dzudzuana Cave in Georgia dating to 26,000 years ago which have around 30% Basal Eurasian ancestry, with the rest being West Eurasian.^[2]

Basal Eurasians may have originated in a region stretching from North Africa to the Middle East, before admixing with West-Eurasian populations.^{[4][5][6][7][8]} North Africa has been described as a strong candidate for the location of the emergence of Basal Eurasians by Loosdrecht et al. in 2018.^[10]

Ferreira et al. in 2021 argued for a point of origin for Basal Eurasians into the Middle East, specifically in the Persian Gulf region on the Arab peninsula. As Basal Eurasians had low levels of Neanderthal ancestry, genetic and archaeological evidence for interactions between modern humans and Neanderthals may allow certain areas, such as the Levant, to be ruled out as possible sources for Basal Eurasians. In other areas, such as southern Southwest Asia, there is currently no evidence for an overlap between modern human and Neanderthal populations.^[7] Vallini et al. 2024 suggests a homeland for Basal Eurasians in the Arabian Peninsula, with a 'Common Eurasian Hub' in the Iranian Plateau, where they diverged into 'Ancient West Eurasians' and 'Ancient East Eurasians'.^[9]

An estimation for Holocene-era Near Easterners (e.g., Mesolithic Caucasus hunter-gatherers, Mesolithic and Neolithic Iranians, and Natufians) suggests that they formed from a combination of Basal Eurasian ancestry, and Western Hunter-Gatherer-related (WHG) and or Ancient North Eurasians-related (ANE) ancestries respectively.^[10] The Mesolithic and Neolithic Iranian lineage is inferred to derived between 38–48% ancestry from Basal Eurasians respectively, with the remainder ancestry being made up by Ancient North Eurasian or Eastern Hunter-Gatherer (EHG) like ancestry, while Natufians derived a mean average of 50% Basal and 50% 'unknown hunter-gatherer' ancestry being closer to Western Hunter-Gatherers (WHG).^{[11][12][13][14]} Alternatively, Mesolithic and Neolithic Iranians derive most of their ancestry from a deep West Eurasian source (WEC2; c. 72%) with c. 18% Basal Eurasian and c. 10% Ancient East Eurasian admixture.^[15] It has been found that the "models of genetic history of West Asian human populations who are modeled as a mixture of ‘basal Eurasians’ and West European hunter–gatherers" is in agreement with the genomic data on 'East Mediterranean Dogs', who "are modeled as a mixture of a basal branch (splitting deeper than the divergence of the Asian and European dogs) and West European dogs".^[16]

The Ancient North African Iberomaurusian (Taforalt) individuals were found to have harbored ~65% West Eurasian-like ancestry and considered likely direct descendants of such "Basal Eurasian" population. However they were shown to be genetically closer to Holocene-era Iranians and Levantine populations, which already harbored increased archaic (Neanderthal) admixture.^[10]

Early European Farmers (EEFs), who had some Western European Hunter-Gatherer-related ancestry and originated in the Near East, also derive approximately 30% (to up to 44%) of their ancestry from this hypothetical Basal Eurasian lineage.^[3][17] An Upper Paleolithic specimen from Kotias Klde cave in the Caucasus (Caucasus_25,000BP) had around 24% Basal Eurasian and 76% Upper Paleolithic European ancestry.^[14]

Among modern populations, Basal-like ancestry peaks among Arabs (such as Qataris) at c. 45%, and among Iranian populations at c. 35%, and is also found in significant amounts among modern Northern Africans, in accordance with the high affinity towards the 'Arabian branch' of Eurasian diversity, which expanded into Northern and Northeastern Africa between 30 and 15 thousand years ago. Modern populations of the Levant derive between 35-38% ancestry from Basal Eurasians, modern Anatolians and populations from the Caucasus derive between 25-30% ancestry from Basal Eurasians, and modern Europeans derive around or less than 20% ancestry from Basal Eurasians.^[7] Modern Bedouins and Yemenis are considered to represent direct descendants of the Basal Eurasians, carrying the highest amount of indigenous 'Arabian ancestry', and being basal to all modern Eurasian populations without displaying higher 'African-associated' admixture, and thus "are among the best genetic representatives of the autochthonous population on the Arabian Peninsula".^[18]