Draft:Genetic history of West Eurasians

This article explains the genetic makeup and population history of Europeans, Middle Easterners, Iranian peoples of South-Central Asia and closely related populations (i.e. North Africans, and, partly, Central Asians, South Asians, and populations of the Horn of Africa), often collectively referred to as "West-Eurasians" in population genomics.

Emergence of the West-Eurasian lineage
The most significant recent dispersal of modern humans from Africa gave rise to an undifferentiated "non-African" lineage by some 70–50 kya (70-50,000 years ago). By about 50–40 kya a West-Eurasian lineage ancestral to modern Europeans, Middle Easterners, South-Central Asians, Northern Africans, and, in part, South Asians, other Central Asians, and populations of the Horn of Africa, had emerged, as had a separate East-Eurasian lineage. Both East and West Eurasians acquired Neanderthal admixture in Europe and Asia. West-Eurasians display deep substructure, specifically there is a "Basal Eurasian" lineage maximized among Middle Easterners, a Caucasus/Iranian lineage maximized among West Asians and South Asians with significant contributions to modern Europeans, and an Mesolithic European/Ancient North Eurasian lineage maximized among modern Uralic-speaking world and representing the West-Eurasian ancestry component among Indigenous peoples of the Americas. It is generally suggested that "Basal Eurasians" represent the first split from East-Eurasians, with Mesolithic Europeans diverging slightly later, although other explanations for this substructure without the need of an earlier split also exists.

During the Last Glacial Maximum, heightened selection pressure and founder effects would result in this West Eurasian meta-population lineage emerging, which would give rise to various closely related but already differentiated subpopulations, such as Western Hunter-Gatherers, Caucasus hunter-gatherers, Natufians, Ancient North Eurasian, Eastern Hunter-Gatherers, and in significant amounts Ancient North Africans (Taforalt) as well as post- AASI ancient South Asians.

Basal Eurasians


Generally, the modern populations inhabiting West Eurasia may not be entirely descended from the West-Eurasian lineage that split from East-Eurasians around 50-40 kya, as they also display ancestry from "Basal Eurasians", a hypothetical lineage which is usually suggested to have diverged slightly before the main ancestry of West-Eurasians diverged from East Eurasians, hence their name, though this is disputed.

The time of divergence between Basal Eurasians, West Eurasians, and East Eurasians is not fully agreed upon, as many sources suggest Basal Eurasians are basal to both West-Eurasians and East-Eurasians, while a few suggest East-Eurasians are basal to Basal Eurasians and other populations of West Eurasia (Mesolithic European Hunter-Gatherers, Ancient North Eurasians).

Basal Eurasians either split from East-Eurasians before Mesolithic European Hunter-Gatherers did, or did not undergo archaic admixture when compared to the West-Eurasian branch which gave rise to Early European modern humans. Several ancient populations in Western Eurasia are suggested to have derived significant amounts of ancestry from Basal Eurasians, most notably groups such as Natufians, Mesolithic Iranians, Neolithic Iranians, and Early European Farmers.

An estimation for Holocene-era Near Easterners (e.g., Mesolithic Caucasian Hunter Gatherers, Mesolithic Iranians, Neolithic Iranians, Natufians) suggests that they formed from up to 50% Basal Eurasian ancestry, with the remainder being closer to Ancient North Eurasians.

Early European Farmers (EEFs), who had some Western European Hunter-Gatherer-related ancestry and originated in the Near East, also derive approximately 44% of their ancestry from this hypothetical Basal Eurasian lineage.

One study suggests Mesolithic European hunter-gatherers generally had no Basal Eurasian ancestry.

However, research professor Leslea Hlusko suggested that Mesolithic European Hunter-Gatherers and Ancient North Eurasians were descended from Basal Eurasians themselves, which would effectively make the Basal-Eurasian and West-Eurasian lineages part of a single lineage basal to East-Eurasians.

The existence of the Basal-Eurasians and own population lineage is questioned by more recent genetic and archaeogenetic data, supporting a repeated population hub expansion, in which West-Eurasians expanded after East-Eurasians, and received less archaic admixture, with the least archaic admixture among Middle Eastern populations. The most basal lineage could be associated with the "Zlatý Kůň" sample, which may form a deep sister clade to early West-Eurasian, however had a distinct position in a worldwide genomic comparison, and did not contribute to any modern humans. They concluded that the ancestors of all non-African populations lived somewhere in southwestern Eurasia, persisted as a single population for at least 15 thousand years after the putative "OoA bottleneck", than split between West-and East-Eurasian populations, marking the beginning of a broader expansion) and later diffused from this “population Hub” ultimately colonizing all of Eurasia and further, with varying degrees of archaic admixture. "We used an approach that integrates genetic with archaeological evidence to model the peopling of Eurasia by Homo sapiens after the Out of Africa (OoA); we infer the presence of an OoA population Hub from which multiple waves of expansion (chronologically, genetically, and technologically distinct) emanated to populate the new continent. We explain the East/West Eurasian population split as a longer permanence of the latter in the OoA Hub, and provide an explanation for the mixed East–West ancestry reported for paleolithic Siberians and, to a minor extent, GoyetQ116-1 in Belgium. We propose a parsimonious placement of Oase1 as an individual related to Bacho Kiro who experienced additional Neanderthal introgression and confirm Zlatý Kůň genetically as the most basal OoA human lineage sequenced to date, also in comparison to Oceanians and putatively link it with non-Mousterian material cultures documented in Europe 48–43 ka."

- Vallini et al. 2022

Hypothetical Basal-Eurasian ancestry peaks among Eastern Arabs (Qataris) and Iranian populations, and is also found in significant amounts among Ancient Iberomarusian samples and modern Northern Africans, in accordance with the Arabian branch of West-Eurasian diversity, which expanded into Northern and Northeastern Africa between 30-15 thousand years ago.



Distinct ancestral components in Western Eurasia
There is no single date in which the ancestors of modern Europeans and Middle Easterners diverged, as they are descended from a variety of West Eurasian-related autosomal DNA components which can be found both in Europe and the Middle East. As such, the genetic distinction between the Middle East and Europe is nebulous. Some Middle Eastern populations share ancestry with European populations that they do not share with other Middle Eastern populations. Such is the case with Levantine populations, who have some ancestry shifted towards Europe rather than the Middle East, and with the Early European Farmers of Neolithic Anatolia (who would go on to contribute significant amounts of ancestry to present-day Europeans), who were genetically distinct from the Zagros farmers of Iran.

The significant genetic differences between ancient Iranians, Neolithic Anatolian farmers and European hunter-gatherers suggests that these populations split before the Neolithic. Assuming a mutation rate of 5 x 10^-10 per site per year, the inferred mean split time for Neolithic Anatolian farmers and European hunter-gatherers ranged from 33-39 kya, and for the Neolithic Iranians 46-77 kya.

One study shows that Ancient Western Iran was inhabited by a population genetically most similar to hunter-gatherers from the Caucasus, but distinct from the Neolithic Anatolian people who later brought agriculture into Europe.

A study of an early Neolithic pastoralist from Zagros, Iran suggests that the Neolithic Central Zagros people were somewhat genetically isolated from other populations of the Fertile Crescent, an isolation which may have begun early on, judging by the lack of affinity to neighboring regions, with Caucasus Hunter-Gatherers having more affinity towards Western Hunter-Gatherers and Neolithic Anatolian Farmers. The results of the study suggest the possibility of gene flow between Caucasus Hunter-Gatherers, Western Hunter-Gatherers, and Neolithic Anatolian Farmers to the exclusion of the Neolithic Iranians. An alternative, but not mutually exclusive, explanation for this pattern is that these Neolithic Iranians might have received genetic input from a source equally distant from all other European populations, and are thus basal to them.

There is high genetic continuity between Early European Farmers and Anatolian hunter-gatherers (~80-90%), suggesting that agriculture was adopted in situ by these hunter-gatherers and not spread by demic diffusion into the region. The existence of this ancient population has been inferred through the genetic analysis of the remains of a male individual from the site of Pınarbaşı (37 ° 29'N, 33 ° 02'E), in central Anatolia, which has been dated at 13,642-13,073 cal BCE. At the autosomal level, in the Principal component analysis (PCA) the analyzed AHG individual turns out to be intermediate between Natufian farmers and Western Hunter-Gatherers (WHG). An adequate two-way admixture model was found, in which the AHG individual derived around half of his ancestry from a Neolithic Levantine-related gene pool (48.0 ± 4.5%; estimate ± 1 SE) and the rest from the Western hunter-gatherer-related one. While these results do not suggest that the AHG gene pool originated as a mixture of Neolithic Levantines and Western hunter-gatherers, both of which lived millennia later than Anatolian hunter-gatherers, it still robustly supports that AHG is genetically intermediate between WHG and Neolithic Levantines. This cannot be explained without gene flow between the ancestral gene pools of those three groups. This supports a late Pleistocene presence of both Near-Eastern and European hunter-gatherer-related ancestries in central Anatolia. Notably, this genetic link with the Levant pre-dates the advent of farming in this region by at least five millenia. found that the ancestors of the EEF had split off from WHG around 43,000 BC, and from Caucasian Hunter-Gatherers (CHGs) around 23,000 BC.

Lazaridis et al. (2014) suggested that the Ancient North Eurasians (ANE) split from Western Hunter-Gatherers around 24,000 BP.

Lazaridis et al. (2015) found that WHGs were a mix of Eastern Hunter-Gatherers (EHGs) and the Upper Paleolithic people (Cro-Magnon) of the Grotte du Bichon in Switzerland. EHGs in turn derived 75% of their ancestry from ANEs. Scandinavian Hunter-Gatherers (SHGs) were found to be a mix of EHGs and WHGs.

One study identified a hypothetical Levantine ancestral component that diverged from other Middle Easterners ∼23,700–15,500 years ago, and diverged from Europeans ∼15,900–9,100 years ago. The study suggests Levantine populations today fall into two main groups: one sharing more genetic characteristics with modern-day Europeans and Central Asians, and the other with closer genetic affinities to other Middle Easterners and Africans.

The populations of the Arab world are characterized by four principal West-Eurasian autosomal DNA components: the Arabian, Levantine, Coptic and Maghrebi components. In the Persian Gulf, the Arabian component is the main autosomal DNA component, which is most closely associated with local Arabic-speaking populations.


 * The Arabian component is also found at significant frequencies in parts of the Levant and Northeast Africa. It represents ∼50% of the individual component in Ethiopians, Yemenis, Saudis, and Bedouins, decreasing towards the Levant, with higher frequency (∼25%) in Syrians, Jordanians, and Palestinians, compared with other Levantines (4%–20%). The geographical distribution pattern of this component correlates with the pattern of the Islamic expansion, but its presence in Lebanese Christians, Sephardi and Ashkenazi Jews, Cypriots and Armenians might suggest that its spread to the Levant could also represent an earlier event. A separate study by Iosif Lazarides and colleagues published in the same year, correlated this component with Epipaleolithic Natufians from the Levant. This study produced genome-wide ancient DNA from 44 ancient Near Easterners between ~12,000 and 1,400 BCE, including Natufian hunter–gatherers, and suggested an earlier spread of Natufian ancestry to populations of the Levant and the Eastern Mediterranean. Natufians were found to be of exclusive West-Eurasian origin, most closely related to modern Arabs, followed by Berber peoples. A 2018 re-analysis of Natufian samples, including 279 modern populations as a reference, found that the Natufians were largely of local West-Eurasian origin, but harbored 6.8% Eastern African-related ancestry, specifically an Omotic component, which peaks among the Aari people. It is suggested that this Omotic component may have been introduced into the Levant along with the specific Y-haplogroup sublineage E-M215, also known as "E1b1b", to Western Eurasia.


 * The Levantine component is the main autosomal element in the Near East and Caucasus. It peaks among Druze populations in the Levant. The Levantine component diverged from the Arabian component about 15,500-23,700 ypb. It is present in Levantines at 42–68%, and at lower frequencies in Europe and Central Asia.


 * The Coptic component peaks among Egyptian Copts in Sudan.


 * The Maghrebi component is the main autosomal element in the Maghreb. It peaks among the non-Arabized Berber populations in the region. Divergence between Maghrebi peoples and Near Eastern/Europeans likely precedes the Holocene (>12,000 ya). The modern Northern African (Berber) populations have been described as a mosaic of Northern African (Maghrebi), Middle Eastern, European, and Sub-Saharan African-related ancestries.

The Ancient North African Taforalt individuals were found to have harbored ~65% West-Eurasian-like ancestry and also shows affinity to the hypothetical "Basal Eurasian" lineage. However they were shown to be genetically closer to Holocene-era Iranians and Levantine populations, which already harbored increased archaic (Neanderthal) admixture.

According to Jones et al. (2015) and Haak et al. (2015), autosomal tests indicate that the Yamnaya people are a mix of Eastern Hunter-Gatherers and a population of Caucasus Hunter Gatherers who probably arrived from the Caucasus or Iran. Each of those two populations contributed about half the Yamnaya DNA. This admixture is referred to in archaeogenetics as Western Steppe Herder (WSH) ancestry.

Modern Europeans are descended from a mix of Western Hunter-Gatherers, Early European Farmers, and Western Steppe Herders.

South Asians
Genetically, South Asians are a composite of West-Eurasian and East-Eurasian components. The first people in South Asia were an East-Eurasian population, dubbed "Ancient Ancestral South Indian". Then several waves of West-Eurasian but also some other East-Eurasian populations entered the subcontinent, mixing with them to form modern-day South Asians. Earliest West-Eurasian ancestry is proposed to have perhaps arrived already during the Paleolithic, about ~40,000 BC and may be linked to expanding Aurignacian groups of the Levant. Genetic data shows that the main West-Eurasian wave, happened during the Neolithic period, or already during the Holocene. According to an international research team led by palaeogeneticists of the Johannes Gutenberg University Mainz (JGU), one of the most important ancestry components of South Asians is derived from a population related to Neolithic farmers from the eastern Fertile Crescent and Iran. They concluded "that the Iranian genomes represent the main ancestors of modern-day South Asians".

Horn of Africa
Horn Africans are a mix of a population indigenous to Ethiopia, dubbed "Ethiopic" ancestry, and ancient West Eurasian ancestry from a back-migration to Africa, dubbed "Ethio-Somali" ancestry.

Native Americans
A genome sequencing of the arm bone of a 24,000 year-old youth from the Mal'ta site suggests that Native Americans derive nearly a third of their ancestry from West-Eurasians, rather than being entirely descended from East-Eurasians as previously thought.

According to Moreno-Mayar et al. 2018 between 14% and 38% of Native American ancestry may originate from gene flow from the Mal'ta–Buret' people (Ancient North Eurasian). This difference is caused by the penetration of posterior Siberian migrations into the Americas, with the lowest percentages of Ancient North Eurasian ancestry found in Eskimos and Alaskan Natives, as these groups are the result of migrations into the Americas roughly 5,000 years ago. Estimates for Ancient North Eurasian ancestry among first wave Native Americans show higher percentages, such as 42% for those belonging to the Andean region in South America. The other gene flow in Native Americans (the remainder of their ancestry) was of East Asian origin.