# 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.
Homo sapiens had left Africa about 70-50,000 years ago, and between 30,000-15,000 years ago migrated back from the Middle East into Northern Africa. About 3,000 years ago, or already earlier between 6,000-5,000 years ago, 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. Moreover, analysis has also recognized that some of the Eurasian ancestry in Northeast Africa could possibly pre-date agriculture, from around ~12-23 ka.
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. West-Eurasian geneflow arrived to Northern Africa during the Paleolithic, followed by other Neolithic migration events. 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". Medieval geneflow events, such as the Arab expansion also left traces in various African populations, but with Neolithization having a much larger demographic impact than Arabization.
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, 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. 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. 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.
A report in November 2015 on a 4,500-year-old Ethiopian genome 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. 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.

## 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.
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."
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.

## Average Eurasian frequencies in African populations

Estimates in Modern Africans :
| African Population Group | Linguistic Affiliation | Proportions of Ancestry |
| Afrikaaner | Indo-European | 97.9% |
| Rashaida Arab | Semitic | 97.92% |
| Canarian | Indo-European | 97.4% |
| Tunisian Jew | Semitic | 96.49% |
| Moroccan Jew | Semitic | 96.05% |
| Libyan Jew | Semitic | 95.76% |
| Chaoui | Berber | 85.12 - 87.51% |
| Moroccan | Semitic | 80% |
| Tunisian | Semitic | 79.37 - 81% |
| Egyptian | Semitic | 79 - 86% |
| Figuig Berber | Berber | 78.98% |
| Bouhria Berber | Berber | 78.68% |
| Mozabite | Berber | 77.33 - 82.39% |
| Asni Berber | Berber | 76.99% |
| Algerian | Semitic | 76.86 - 82.45% |
| Libyan | Semitic | 76% |
| Saharawi | Semitic | 74.32 - 84.9% |
| Tigrayan | Ethio-Semitic | 50 - 50.4% |
| Beja | Cushitic | 50% |
| Amhara | Ethio-Semitic | 49.2 - 54% |
| Ethiopian Jew | Semitic | 46.4 - 55.12% |
| Afar | Cushitic | 46.0% |
| Kababish Arab | Semitic | 45.99% |
| Oromo | Cushitic | 41.6 - 51% |
| Agaw | Cushitic | 41 - 50% |
| Sudanese Arab | Semitic | 40 - 52.73% |
| Nubian | Nilo-Saharan | 39.41 - 54.74% |
| Somali | Cushitic | 38.4 - 44% |
| Cape Verdean | Indo-European | 36 - 54% |
| Wolayta | Omotic | 34.1 - 43% |
| Samburu | Nilo-Saharan | 32.19% |
| Datooga | Nilo-Saharan | 32.17% |
| Malagasy | Austronesian | 30 - 68% |
| Baggara Arab | Semitic | 25.57 - 33.6% |
| Fulani | Niger-Congo | 21.4 - 29% |
| Toubou | Nilo-Saharan | 20 - 31.4% |
| Maasai | Nilo-Saharan | 18.9 - 26.06% |
| Turkana | Nilo-Saharan | 18.33% |
| Aari | Omotic | 15.7 - 18.2% |
| Sandawe | Khoisan | 15.4% |
| Nama | Khoisan | 14% |
| Kikuyu | Niger-Congo | 13.89 - 18.33% |
| Zaghawa | Nilo-Saharan | 12.58% |
| Kalenjin | Nilo-Saharan | 10.99 - 12.86% |
| Kanembu | Nilo-Saharan | 10.97% |
| Hadza | Khoisan | 6.4 - 12.71% |
Estimates in Ancient African Samples :
| African Population | Time Period | Number | Proportions of Ancestry |
| Egypt, Nuerat Egyptian | 2,868 - 2,492 BC | N=1 | 90% |
| Canary Islands, Guanche | 3rd - 16th Century CE | N=40 | 89.4% |
| Morocco, SKH (Skhirat-Rouazi) | 6733 - 6121 BP | N=3 | 87% |
| Morocco, KTG (Kaf Taht el-Ghar) | 7429 - 6945 BP | N=4 | 86% |
| Algeria, Numidian | 1 - 700 CE | N=1 | 85.87% |
| Egypt, Abusir-el-Meleq Egyptian | 1388 BCE - 426 CE | N=3 | 85 - 94% |
| Morocco, KEB (Khef el-Baroud) | 3000 BCE | N=8 | 81.75% |
| Tunisia, Hergla | 5900 BP | N=1 | |
| Tunisia, Carthaginian | 650 - 250 BCE | N=12 | 77.33 - 97.3% |
| Tunisia, DEK (Doukanet el Khoutifa) | 7000 - 6600 BP | N=5 | |
| Sudan, Kulubnarti Nubian | 650 -1000 CE | N=66 | 46 - 64% |
| Morocco, IAM (Ifri n'Amar) | 5000 BCE | N=7 | |
| Tunisia, Djebba | 8000 BP | N=2 | |
| Morocco, OUB (Ifri Ouberrid) | 7660 - 7506 BP | N=1 | |
| Algeria, ABR (Afalou Bou Rhummel) | 10,000 BP | N=1 | |
| Morocco, Iberomaurusian | 15,100 - 13,900 YBP | N=7 | 46 - 63.5% |
| Sudan, Kadruka Nubian | 4033 BP | N=1 | 45.2% |
| Tanzania, Luxmanda | 3141 - 2890 BP | N=1 | 37.2 - 39% |
| Kenya, Pastoral Neolithic | 3500 - 1500 BP | N=41 | 30 - 40% |
| Tanzania, Swahili | 1250 - 1800 AD | N=80 | 26 - 68% |
| Libya, Takarkori | 7,000 YA | N=2 | 20 - 30% |