Eurasian backflow

The term Eurasian backflow, or Eurasian back-migrations, has been used to describe several pre-Neolithic and Neolithic migration events of humans from western Eurasia back to Africa.^[1]

Pre-Neolithic and Neolithic migration events in Africa.^[2]

Homo sapiens had left Africa about 70-50,000 years ago,^[3][4][5] and between 30,000-15,000 years ago migrated back from the Middle East into Northern Africa. About 3,000 years ago,^[6][7] or already earlier between 6,000-5,000 years ago,^[8] farmers from Anatolia and the Near East migrated into the Horn of Africa. Signs of this migration can be found in the genomes of contemporary peoples from all over East Africa.^[1][9] Moreover, analysis has also recognized that some of the Eurasian ancestry in Northeast Africa could possibly pre-date agriculture, from around ~12-23 ka.^[10] Next to Eastern Africa, significant Eurasian ancestry is found in Northern Africa, and among specific ethnic groups of the Horn of Africa, Northern Sudan, the Sahel region, as well as among the Malagasy people of Madagascar. Various genome studies found also evidence for multiple pre-historic back-migrations from various Eurasian populations and subsequent admixture with native groups.^[11] West-Eurasian geneflow arrived to Northern Africa during the Paleolithic, followed by other Neolithic migration events.^[6] Genetic data on the Taforalt samples "demonstrated that Northern Africa received significant amounts of gene-flow from Eurasia predating the Holocene and development of farming practices".^[12] Medieval geneflow events, such as the Arab expansion also left traces in various African populations,^[13] but with Neolithization having a much larger demographic impact than Arabization.^[14][15]

Map of major prefarming population stratification across the African continent.^[16]

The people migrating back to Africa were closely related to the Neolithic farmers who had brought agriculture from the Near East to Europe about 7,000 years ago. This population is also closely related to present-day Sardinians,^[1] although studies have made distinctions between the population that brought farming into Europe and Maghreb, and the Levantine related groups that spread southward into East Africa.^[17][18] A study from 2020 inferred two sources for the spread of Eurasian admixture in Northeastern Africa, with one associated with pastoralism. The initial phase involved groups originating from the Levant and North Africa that gave rise to the Pastoral Neolithic.^[19] Further research has shown that the back-migration into the region was a complex process, identifying multiple origins for the Eurasian component in Northeast African groups today.^[20][21]

A report in November 2015 on a 4,500-year-old Ethiopian genome^[22][23] had originally overestimated the genetic influence of the Eurasian backflow, claiming that signs of the migration could be found in genomes all over Africa. This mistaken claim was based on a data-processing error and was corrected in February 2016. The West Asian admixture was only predominant in the populations of the Horn of Africa, in particular Ethiopian highlanders, and less relevant or absent in the genetic makeup of West and Central Africans.^[9] In addition to intrinsic diversity within the continent borne by population structure and isolation, influxes of Eurasian populations into Africa has been seen as a critical contributor to the existing genetic diversity.^[24]

Neanderthal admixture and Eurasian ancestry

An investigation in 2012 discovered that unlike most sub-Saharan Africans, North Africans have similar levels of Neanderthal DNA to South Europeans and West Asians, which is pre-Neolithic in origin, rather than via any recent admixture, as the Neanderthal's genetic signals were higher in populations with an autochthonous 'back-to-Africa' genomic component that arrived 12,000 years ago. These Neanderthal genomic traces do not mark a division between Africans and non-Africans, but rather a division between sub-Saharan Africans and the rest of the modern human groups, including those from North Africa.^[25]

In 2016, researchers recognized that the Neanderthal ancestry in African populations, strongly corresponds with the levels of Western Eurasian ancestry. The geneticists elaborated that: "Neanderthal ancestry is not expected in Africa, yet today many Africans carry Neanderthal-derived alleles. The plot shows that the Neanderthal ancestry proportion in Africans is correlated with gene flow from Eurasians. For example, knowing that today Eurasians carry ~2% of Neanderthal ancestry, we observed that East Africans (Ethiopians) had ~1% Neanderthal ancestry and ~50% Eurasian ancestry. Correspondingly, Near Easterners showed a decline in Neanderthal ancestry proportional to their levels of African ancestry."^[26]

Human dispersals within Africa

Chen, Lu's publication found back-migrations contributed to the signal of Neanderthal ancestry in Africans. Data indicated that back-migrations giving Neanderthal sequences came after the split of Europeans and East Asians, from populations related to the European lineage. The overlap of this ancestral European ancestry and Neanderthal segments was highly significant.^[27]

Average Eurasian frequencies in African populations

Estimates in Modern Africans

African Population Group	Linguistic Affiliation	Proportions of Ancestry
Afrikaaner	Indo-European	97.9%[28]
Rashaida Arab	Semitic	97.92%[29]
Canarian	Indo-European	97.4%[30]
Tunisian Jew	Semitic	96.49%[31]
Moroccan Jew	Semitic	96.05%[31]
Libyan Jew	Semitic	95.76%[31]
Chaoui	Berber	85.12 - 87.51%[32]
Moroccan	Semitic	80%[33]
Tunisian	Semitic	79.37 - 81%[31][34]
Egyptian	Semitic	79 - 86%[33][35][36]
Figuig Berber	Berber	78.98%[29]
Bouhria Berber	Berber	78.68%[29]
Mozabite	Berber	77.33 - 82.39%[31][33][32]
Asni Berber	Berber	76.99%[29]
Algerian	Semitic	76.86 - 82.45%[31][32]
Libyan	Semitic	76%[37]
Saharawi	Semitic	74.32 - 84.9%[31][37]
Tigrayan	Ethio-Semitic	50 - 50.4%[38][39]
Beja	Cushitic	50%[40]
Amhara	Ethio-Semitic	49.2 - 54%[39][35][41]
Ethiopian Jew	Semitic	46.4 - 55.12%[42][31]
Afar	Cushitic	46.0%[39]
Kababish Arab	Semitic	45.99%[29]
Oromo	Cushitic	41.6 - 51%[39][41]
Agaw	Cushitic	41 - 50%[43]
Sudanese Arab	Semitic	40 - 52.73%[13][29]
Nubian	Nilo-Saharan	39.41 - 54.74%[13][29]
Somali	Cushitic	38.4 - 44%[39][44][31][41]
Cape Verdean	Indo-European	36 - 54%[45][46]
Wolayta	Omotic	34.1 - 43%[39][41]
Samburu	Nilo-Saharan	32.19%[29]
Datooga	Nilo-Saharan	32.17%[31]
Malagasy	Austronesian	30 - 68%[47][48]
Baggara Arab	Semitic	25.57 - 33.6%[29]
Fulani	Niger-Congo	21.4 - 29%[49][50]
Toubou	Nilo-Saharan	20 - 31.4%[51][37]
Maasai	Nilo-Saharan	18.9 - 26.06%[39][31]
Turkana	Nilo-Saharan	18.33%[29]
Aari	Omotic	15.7 - 18.2%[39]
Sandawe	Khoisan	15.4%[39]
Nama	Khoisan	14%[39]
Kikuyu	Niger-Congo	13.89 - 18.33%[42][31]
Zaghawa	Nilo-Saharan	12.58%[29]
Kalenjin	Nilo-Saharan	10.99 - 12.86%[42][29]
Kanembu	Nilo-Saharan	10.97%[29]
Hadza	Khoisan	6.4 - 12.71%[39][31]

Estimates in Ancient African Samples

African Population	Time Period	Number	Proportions of Ancestry
Egypt, Nuerat Egyptian	2,868 - 2,492 BC	N=1	90%[52]
Canary Islands, Guanche	3rd - 16th Century CE	N=40	89.4%[30]
Morocco, SKH (Skhirat-Rouazi)	6733 - 6121 BP	N=3	87%[53][54]
Morocco, KTG (Kaf Taht el-Ghar)	7429 - 6945 BP	N=4	86%[53][54]
Algeria, Numidian	1 - 700 CE	N=1	85.87%[55]
Egypt, Abusir-el-Meleq Egyptian	1388 BCE - 426 CE	N=3	85 - 94%[36]
Morocco, KEB (Khef el-Baroud)	3000 BCE	N=8	81.75%[56]
Tunisia, Carthaginian	650 - 250 BCE	N=12	77.33 - 97.3%[57][58]
Sudan, Kulubnarti Nubian	650-1000 CE	N=66	46 - 64%[59]
Morocco, IAM (Ifri n'Amar)	5000 BCE	N=7	[56]
Morocco, OUB (Ifri Ouberrid)	7660 - 7506 BP	N=1	[53]
Morocco, Iberomaurusian	15,100 - 13,900 YBP	N=7	46 - 63.5%[43][60]
Sudan, Kadruka Nubian	4033 BP	N=1	45.2%[61]
Tanzania, Luxmanda	3141 - 2890 BP	N=1	37.2 - 39%[62]
Kenya, Pastoral Neolithic	3500 - 1500 BP	N=41	30 - 40%[63][64]
Tanzania, Swahili	1250 - 1800 AD	N=80	26 - 68%[65]
Libya, Takarkori	7,000 YA	N=2	20 - 30%[66]

See also

• African admixture in Europe
• Genetic history of Africa
• Genetic history of North Africa
• Genetic history of the African diaspora
• Neolithic Revolution