The Yamnaya Steppe Herders from Russia Jan 14, 2017 20:35:37 GMT
Post by Admin on Jan 14, 2017 20:35:37 GMT
Climate shifts dramatically influenced the occupation of Southwest Asia by anatomically modern humans since their first occupation at the sites of Skhul and Qafzeh in Israel some 80 to 130 ka1. These first archaeologically identified modern humans outside of Africa appear to have left no genetic impact, with the next modern human remains in the Levant dating to around 45–50 ka1. Climate change impacts on population mobility and cultural developments have been hotly debated2. Aridity restricted larger human populations to refugia sited around the Mediterranean3, the Black Sea4, and possibly the southern Arabian Peninsula5, that were distinguished by tool cultures in the archaeological record6,7, during the Last Glacial Period (LGP) ending some 12 ka. Post-glacial warming, and later, agriculture, allowed expansions of these populations within SW Asia8. Archaeological evidence shows post-LGP population expansions shifting from mobile foraging to a more sedentary lifestyle4,9 with permanent settlements, early cultivation of wild plants10,11, stored goods, and emerging trade and exchange networks12,13. The Fertile Crescent based “Neolithic Revolution” replaced most cultures across the region, spreading Indo-European languages from an Anatolian homeland14, both westward to Europe, northward to the steppes, and eastward to the Iranian plateau and beyond.
Autosomal analyses have identified a cryptic population, “Basal Eurasians,” that injected significant genetics into the European population distinct from the Southwest Asian agricultural revolution signature15. Subsequent work16,17 has suggested that Yamnaya aDNA appears to have been a source of the genetics associated with corded ware culture, and provides further evidence for a late Neolithic through early Bronze Age wave introducing Indo-European languages.
Lineages that evolved in relatively isolated refugia populations could carry genetic evidence of that isolation and subsequent expansion. Such signals identified source populations for admixture events marking European settlement15,16,18,19. However, specific associations between Southwest Asian post-LGP expansion genetics and their original refugia, and the identification of the timing and directions of their various dispersal events, are still being determined. Most recently, analyses of complete mitochondrial genomes have identified a possible Arabian refugia in the LGP, within which several mtDNA haplogroups including R0a emerged and from which they dispersed to the Fertile Crescent, the Levant and the Horn of Africa20. Y-chromosome analysis has identified highest frequencies for J1 haplogroup to be most common in the Saudi Peninsula21 marking the Muslim expansion22 with J2 being common in the coastal Levant23, and identified early on as a possible marker of the European expansion of the post-Neolithic expansion8,24, while their origins have been identified roughly within Iran, Armenia, Georgia, and/or Eastern Turkey. However, even though J2 appeared to mark a post-Neolithic expansion, this haplogroup has been identified in ancient DNA analysis of remains archaeologically associated with the late Bronze Era25. Both Haplogroups origins have been identified roughly within Iran, Armenia, Georgia, and/or Eastern Turkey.
Here, we take the approach of identifying and dating population isolation prior to expansion, and tracing routes of dispersal throughout Southwest Asia and into Europe and Africa. We analyzed a comprehensive autosomal and Y-chromosome dataset of Eurasian and African populations identifying genetic signals of regional LGP population isolation, and contrasted expansion time estimates and dispersal routes in the region with archaeological4,9, palaeontological26, palaeobotanical27, and climate4,27 data.