Sanchez-Quinto et al (1) analyzed shared ancient genome of European farmers 9kya that indicated these hunter-gatherers carried U5 and were in communication from Iberia to Central Europe. These researchers are correct to emphasize the unity between these geographically diverse groups (1).
Sanchez-Quinto et al (1) suggest that the U5 lineage probably originated in Central Europe and evidence a back-to-Africa migration. This hypothesis lacks continuity because the populations with the highest frequencies of the U5 cline are found either in Northwest Africa (NWA) or Sub-Saharan West Africa (SSWA).
A phylodemographic analysis of contemporary Europeans indicate that only 4%-7% Europeans carry the U5 lineage(2). This discontinuity of the European genetic landscape manifest questions on the ancestry of the ancient European hunter-gatherers. The genetic data would make the source of U5 in the western parts of Africa—not Eurasia.
Malyarchuck et al (2) believes that the U5 lineage arrived in Europe with the Aurignacian culture bearers. This seems highly unlikely because the Aurignacians carried mtDNA L3(N) when they crossed the Straits of Gibraltar 40kya (3). As illustrated by Haak et al , ancient mtDNA indicates that hunter-gatherers belonging to the N1a haplogroup was the predominate genome among the Aurignacians up to 9 kya (3). Consequently, the genetic evidence suggest a replacement of the Aurignacians by a populations carrying the U5 clades.
The closest European population to the ancient European hunter-gatherers are the Saami of Scandinavia. The Saami carry the highest frequencies of the U5 lineage (6). The predominate Saami U5 clade is U5b1b1. Whereas only 4% of contemporary Europeans carry U5, 50% of the Saami belong to U5b.
The highest concentration of U5 is found among Berbers in NWA (4). It is also carried by Mande and Fulani Niger-Congo speakers in West Africa (5-8).
The U5 haplogroup carried by the Mande, like other SSWA is characterized by 16189,16192,16270 and 16320. There is a high frequency of U5 among the Fulani who mainly belongs to U5b1b (5-8) and U5a (4-8). Interestingly, U5b1b links the Saami of Scandinavia and the Yakuts to the Fulani and NWA Berbers (6,9).The frequency of U5 in SSWA and NWA suggest demic diffusion of these populations across the Straits of Gibraltar into Iberia and thence Central Europe.
Achilli et al (9) has argued that there was a back migration of the U5 cline across the Straits of Gibraltar. This hypothesis lacks congruence given the early date of U5 in Iberia, in comparison to Central Europe; and the presence of diverse sub-clades of U5 distributed across SSWA among diverse populations which fail to record a history of mating with Berber populations. Moreover it is clear that groups such as the Fulani are of African origin and show no history of admixture with Europeans (10).
Rosa et al (6) claims an autochthonous origin for haplogroup U6 in NWA given the diversity of U6 clades in NWA around 38kya. Using this criterion, the diversity of U5 clades in SSWA and the phylogeography of U5 in this region, support an in situ origin for the U5 clade in the same region as haplogroup U6.
In summary, the genetic data from contemporary European populations fails to support a migration of populations carrying haplogroup U5 into Europe via the Levant. The low frequency of U5 in Europe, except among the Saami, probably indicates a single episode of ancient gene flow from NWA and SSWA into Iberia 9kya. The present phylogeograpical distribution of the U5 cline reflects demographic porcesses involving population replacement, drift and a history of genetic bottlenecks resulting from demic diffussion of neolithic populations from the Levant and Central Asia into Europe.
The temporal and spatial distribution of U5 and U6 clades outside Europe, point to a NWA and SSWA origin for these lineages. The high frequency of U5 in NWA and SSWA suggest the spread of the U5 cline into Iberia across the Straits of Gibraltar 7kya.
Reference:
1. Federico Sánchez-Quinto, Hannes Schroeder, Oscar Ramirez, María C. Ávila-Arcos, Marc Pybus, Iñigo Olalde, Amhed M.V. Velazquez, María Encina Prada Marcos, Julio Manuel Vidal Encinas, Jaume Bertranpetit, Ludovic Orlando, M. Thomas P. Gilbert, Carles Lalueza-Fox.2012. Genomic Affinities of Two 7,000-Year-Old Iberian Hunter-Gatherers. Current Biology ; DOI: 10.1016/j.cub.2012.06.005
2.Malyarchuck B, Derenko M, Grzybowski T, Perlova M, Rogalla U et al.2010. The peopling of Europe from the Mitochodrial Haplogroup U5 Perspective. PlosOne 5(4): http://www.plosone.org/article/info:doi/10.1371/journal.pone.0010285
3. Winters C .2011. The Gibraltar Out of Africa Exit for Anatomically Modern Humans . WebmedCentral BIOLOGY 2(10):WMC002319 . http://www.webmedcentral.com/article_view/2319
4. Rando J.C., Pinto F., Gonzalez A.M., Hernandez M., Larruga J.M., Cabrera V.M. & Bandelt H.J. 1998. Mitochondrial DNA analysis of northwest African populations reveals genetic exchanges with European, near-eastern, and sub-Saharan populations. Ann. Hum. Genet., 62: 531-550.
5. Cerný V., Hajek M., Bromova M., Cmejla R., Diallo I. & Brdicka R. 2006. MtDNA of Fulani nomads and their genetic relationships to neighboring sedentary populations. Hum. Biol., 78: 9-27.
6. Rosa A, Brehem A. 2011. African human mtDNA phylogeography at-a-glance. J. Anthropol. Sci, 89:25-58.
7. Coia V., Destro-Bisol G., Verginelli F., Battaggia C., Boschi I., Cruciani F., Spedini G., Comas D. & Calafell F. 2005. Brief communication: mtDNA variation in North Cameroon: lack of Asian lineages and implications for back migration from Asia to sub-Saharan Africa. Am. J. Phys. Anthropol., 128: 678-681.
8. Ely B., Wilson J.L., Jackson F. & Jackson B.A. 2006. African-American mitochondrial DNAs often match mtDNAs found in multiple African ethnic groups. BMC. Biol., 4: 34.
9.Achilli A, Rengo C, Battaglia V, Pala M, Olivieri A, et al. 2005. Saami and Berbers – an unexpected mitochondrial DNA link. Am J Hum Genet 76: 883–886.
10. Winters C. 2010. The Fulani are not from the Middle East. PNAS . http://www.pnas.org/content/107/34/E132.extract
