Basal Eurasian is a proposed lineage of anatomically modern humans with reduced, or zero, archaic hominin (Neanderthal) admixture 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]

Description

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).[2] 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.[3][4][5][6][7]

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.[4]

Possible geographic origins

Basal Eurasians may have originated in a region stretching from North Africa to the Middle East, before admixing with West-Eurasian populations.[3][4][5][6][7] North Africa has been described as a strong candidate for the location of the emergence of Basal Eurasians by Loosdrecht et al. in 2018.[8] 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.[6]

Estimated Basal Eurasian ancestry in ancient and modern populations

Admixture graph model showing Basal Eurasian branch according to Wang et al. 2019

An estimation for Holocene-era Near Easterners (e.g., Mesolithic Caucasus hunter-gatherers, Mesolithic and Neolithic Iranians, and Natufians) suggests that they formed from up to 70% Basal Eurasian ancestry (mean average 50% Basal and 50% 'unknown hunter-gatherer'), with the remainder being closer to Western Hunter-Gatherers (WHG) and or Ancient North Eurasians (ANE).[8] The Mesolithic and Neolithic Iranian lineage is inferred to derived around 66% (66±13%) and 62% 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 between 60-70% ancestry from Basal Eurasians, with the remainder ancestry being closer to Western Hunter-Gatherers (WHG).[9][10]

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.[8]

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.[2][11]

Among modern populations, Basal Eurasian 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 20% ancestry from Basal Eurasians.[6] Modern Bedouins and Yemenis are considered to represent direct descedants 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".[12]

References

  1. ↑ Quilodrán, Claudio S.; Rio, Jérémy; Tsoupas, Alexandros; Currat, Mathias (2023-10-20). "Past human expansions shaped the spatial pattern of Neanderthal ancestry". Science Advances. 9 (42). doi:10.1126/sciadv.adg9817. ISSN 2375-2548. PMC 10584333. PMID 37851812.
  2. 1 2 Lazaridis et al. 2014.
  3. 1 2 Kamm et al. 2020.
  4. 1 2 3 Bergström et al. 2021.
  5. 1 2 Vallini & Pagani 2022.
  6. 1 2 3 4 Ferreira et al. 2021.
  7. 1 2 Lazaridis et al. 2016.
  8. 1 2 3 van de Loosdrecht et al. 2018.
  9. ↑ Lazaridis, Iosif; Nadel, Dani; Rollefson, Gary; Merrett, Deborah C.; Rohland, Nadin; Mallick, Swapan; Fernandes, Daniel; Novak, Mario; Gamarra, Beatriz; Sirak, Kendra; Connell, Sarah; Stewardson, Kristin; Harney, Eadaoin; Fu, Qiaomei; Gonzalez-Fortes, Gloria (August 2016). "Genomic insights into the origin of farming in the ancient Near East". Nature. 536 (7617): 419–424. doi:10.1038/nature19310. ISSN 1476-4687. PMC 5003663. Neolithic Iran and Natufians could be derived from the same Basal Eurasian population but are genetically closer to EHG and WHG respectively. We take the model of Fig. S4.9 and attempt to fit Natufians as a mixture of the same Basal Eurasian population that contributes to Iran_N and any other population of the tree. Several solutions are feasible, and we show the best one (lowest ADMIXTUREGRAPH score) in Fig. S4.10. We can add both EHG and MA1 as simple branches to the model structure of Fig. S4.10 and show the results in Fig. S4.11. An interesting aspect of this model is that it derives both Natufians and Iran_N from Basal Eurasians but Natufians have ancestry from a population related to WHG, while Iran_N has ancestry related to EHG. Natufians and Iran_N may themselves reside on clines of WHG-related/EHG-related admixture.
  10. ↑ Ferreira, Joana C; Alshamali, Farida; Montinaro, Francesco; Cavadas, Bruno; Torroni, Antonio; Pereira, Luisa; Raveane, Alessandro; Fernandes, Veronica (2021-09-04). "Projecting Ancient Ancestry in Modern-Day Arabians and Iranians: A Key Role of the Past Exposed Arabo-Persian Gulf on Human Migrations". Genome Biology and Evolution. 13 (9): evab194. doi:10.1093/gbe/evab194. ISSN 1759-6653. PMC 8435661. PMID 34480555. It has been previously speculated that isolated basal Eurasian lineage descendants in the central Zagros Mountains of Iran, who were the first goatherds, spread afterwards into the Eurasian steppe (Broushaki et al. 2016; Lazaridis et al. 2016). Also the ancient Iberomaurusian specimens could be in part descendants of basal Eurasians (van de Loosdrecht et al. 2018)
  11. ↑ Lipson, Mark; Szécsényi-Nagy, Anna; Mallick, Swapan; Pósa, Annamária; Stégmár, Balázs; Keerl, Victoria; Rohland, Nadin; Stewardson, Kristin; Ferry, Matthew; Michel, Megan; Oppenheimer, Jonas; Broomandkhoshbacht, Nasreen; Harney, Eadaoin; Nordenfelt, Susanne; Llamas, Bastien (November 2017). "Parallel palaeogenomic transects reveal complex genetic history of early European farmers". Nature. 551 (7680): 368–372. doi:10.1038/nature24476. ISSN 1476-4687. PMC 5973800.
  12. ↑ Rodriguez-Flores, Juan L.; Fakhro, Khalid; Agosto-Perez, Francisco; Ramstetter, Monica D.; Arbiza, Leonardo; Vincent, Thomas L.; Robay, Amal; Malek, Joel A.; Suhre, Karsten; Chouchane, Lotfi; Badii, Ramin; Al-Marri, Ajayeb Al-Nabet; Khalil, Charbel Abi; Zirie, Mahmoud; Jayyousi, Amin (2016-02-01). "Indigenous Arabs are descendants of the earliest split from ancient Eurasian populations". Genome Research. 26 (2): 151–162. doi:10.1101/gr.191478.115. ISSN 1088-9051. PMC 4728368. PMID 26728717. Given that the Q1 (Bedouin) have the greatest proportion of Arab genetic ancestry measured in contemporary populations (Hodgson et al. 2014; Shriner et al. 2014) and are among the best genetic representatives of the autochthonous population on the Arabian Peninsula, these two conclusions therefore point to the Bedouins being direct descendants of the earliest split after the out-of-Africa migration events that established a basal Eurasian population (Lazaridis et al. 2014). This is also consistent with the majority of Q1 (Bedouin) being able to trace a significant portion of their autosomal ancestry through lineages that never left the peninsula after the out-of-Africa migration events since such deep ancestry would not be expected if the entire Arabian Peninsula population had been reestablished from Africa or a non-African population at a later point.

Sources

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