The end of the last Ice Age ca. 14000-12000 BC brought instability to the Pontic-Caspian zone: meltwater flew torrentially from the northern glaciers and the permafrost into the Khvalynian Sea (the Caspian Sea is a small remaining part of it), and a shoreline between the middle Volga and the Ural River restricted east-west movements south of the Ural Mountains[Anthony 2007].
By 11000-9000 BC water may have poured into the Black Sea[Major et al. 2006][Ryan 2007], enlarging it and creating the Sea of Azov. Although the magnitude and rapidity of this flow remains controversial[Yanko-Hombach, Gilbert, and Dolukhanov 2007], it is agreed that meltwater created unstable shores in this area.
Deglaciation and palaeoclimatic changes were probably more important in their potential for environmental, cultural, social and historical changes of this region, though. A significant deterioration is found during the Younger Dryas – Pre-Boreal period caused by climate aridization and reduction of overall biomass density in the region, with large group segmentation, local population dispersion, increase in population mobility, and decrease in population density[Smyntina 2016].
In the Boreal period, the Pontic-Caspian steppe became stable with an increase in climatic humidity, and a growth of biomass density. Hunters – probably from eastern and western regions – settled there and population density increased. The different migration times and paths of R1a-M420 and R1b-M343 lineages puts the Ural-Caspian frontier as a linguistic and cultural barrier that might have been crossed around this time period.
R1b1a1a-P297 formation (ca. 14800 BC) and TMRCA (ca. 11300 BC), and the formation of R1b1a1a2-M269 (ca. 11300 BC) compared to its quite late TMRCA (ca. 4300 BC) point to a slow spread of hunter-gatherer groups of R1b1a1a-P297 lineages in east Europe coinciding with the geographic changes associated with the last deglaciation.
To the north, the population of the final Palaeolithic Swiderian culture, which developed in Poland on the sand dunes left behind by retreating glaciers, migrated during the Palaeolithic-Mesolithic transition (ca. 9500 BC) to the north-east following the retreating tundra, which is evidenced by a 300-year-long settlement break before a new population arrived[Kobusiewicz 2002]. Post-Swiderian cultures developed in the Baltic and in the Forest Zone north of the unstable Pontic-Caspian zone, and it seems reasonable to assume an eastern and south-eastern migration of hunters into the now open areas.
Samples of R1b1a1a-P297 (xR1b1a1a2-M269) have been found in Latvian hunter-gatherers continuously in different periods, dated from the end of the 9th millennium BC to the end of the 4th millennium BC, including Kunda and Narva cultures[Jones et al. 2017][Mathieson et al. 2017].
Old traditions from the northern Black Sea region that survived the Younger Dryas migrated into new areas: the Anetivka tradition from the west expanded to the north of the Dniester, to the east in the Dnieper, and to the south penetrating the Crimean Peninsula; and the Grebenniki culture (derived from the Tsarinka flint knapping tradition) expanded west from the Lower Volga, sharing the same areas as Anetivka settlements. To the east, new traditions appeared[Smyntina 2016].
The oldest aDNA sample of R1a-M420 lineage found in east Europe was at Vasylivka, dated ca. 8690 BC, at the same site where a sample dated ca. 7250 BC was found of haplogroup R1b1a2-V88[Mathieson et al. 2017].
Diachronic map of Palaeolithic migrations.
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