R1a-M420 and East Hunter-Gatherers
Haplogroup R1a-M420 originated ca. 25000 BC, and was proposed to diverge initially in the vicinity of present-day Iran based on a study of modern populations[Underhill et al. 2015].
Eastern Hunter-Gatherer (EHG) ancestry is represented by two individuals from Karelia – one of haplogroup R1a1a1-M417 (ca. 6425 BC) and the other of haplogroup J (ca. 5250 BC) – and one individual from Samara (ca. 5600 BC), of haplogroup R1b1a1a-P297[Mathieson et al. 2017]. It has more ANE ancestry than any other ancient or modern population[Haak et al. 2015], being close to the sample from Afontova Gora (ca. 15980 BC), to the west of Lake Baikal.
The oldest aDNA sample of R1a-M420 lineage found in east Europe was at Vasylivka, dated ca. 8690 BC, at the same site of a later sample of haplogroup R1b1a2-V88, dated ca. 7250 BC[Mathieson et al. 2017]. These and other three Mesolithic samples from Ukraine show an intermediate situation between EHG and Scandinavian Hunter-Gatherer ancestry. Later, during the transition of the Mesolithic to Neolithic, a decrease in ANE ancestry and an increase in WHG ancestry is observed.
We have seen that the Villabruna cluster (and associated Mesolithic R1b-M343 lineages found from west to east Europe) might be the representatives of the expansion of West Hunter-Gatherer ancestry, displacing or admixing with the existing population of western Europe. On the other hand, hunter-gatherers from the Iron Gates show WHG (87%) and EHG (13%), and mtDNA haplogroups that contrast with the prevalent haplogroups U5 or U2 of WHG, EHG, and Scandinavian hunter-gatherers[Mathieson et al. 2017].
R1b-M343 lineages may have thus brought WHG ancestry to the north Pontic steppe during the Mesolithic, either from south-eastern Europe or from the Swiderian culture (see above). Supporting this eastern migration, samples of R1b1a1a-P297 (xR1b1a1a2-M269) lineage 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].
These Baltic samples show an intermediate ancestry between western and eastern hunter-gatherers, of ca. 70% WHG and 30% EHG, before an increase in EHG is seen during the Neolithic Comb Ware culture expansion (see Forest Zone). The sample from Afontova Gora 3 (ca. 15980 BC) of the Late Palaeolithic Siberian complex (with cultural and genetic links to the people from Mal’ta Buret’), shows a common cluster in PCA analysis with samples from the eastern steppe of the Mesolithic, Neolithic, and Chalcolithic[Mathieson et al. 2017] .
Haplogroup R1a1a1-M417 (formed ca. 6500 BC, TMRCA ca. 3500 BC) is first found in the Karelian hunter-gatherer dated ca. 6425 BC. Two samples of R1a1a1-M417, dated ca. 5250 BC, have also been found in Early Neolithic Baikalic cultures near the zone where the ancient Mal’ta-Buret’ culture was located. Strontium isotope ratios confirm their local origin, with high paternal heterogeneity, with a trend to replacement by east Eurasian lineages during the Late Neolithic[Moussa et al. 2016].
A migration of R1a-M420 lineages from the Iranian area to the forests of Eastern Europe has been previously proposed[Horvath 2015].
Given the Eurasian origin of the eastern European pottery (see Mesolithic-Neolithic transition) and its westward expansion into Europe, the likely eastern origin of EHG ancestry and R1a1a1-M417 lineages, it seems logical to find a common origin of both populations (from eastern Europe and the Baikal region) in an expansion from Eurasian territory, dated around the subclade’s formation date.
The traditional association of Forest Zone hunter-gatherers’ expansion with hunters of the Kelteminar culture, would imply a date ca. 5500 BC, which is too late for the attested samples. Ancestors of this population are supposed to have originally migrated from the Hissar range ca. 6000 BC, though, with an earlier expansion from a neighbouring area potentially fitting the available data.
Because of the early sample of R1a-M420 found in the Mesolithic north Pontic area, and maybe also the rare subclade R1a5-Z645 found in Estonia[Saag et al. 2017], it could be proposed that the migration of R1a-M420 subclades (including R1a1a1-M417) happened from the north-west Pontic area, with a back-migration of these lineages to the Baikal region. However, given the available archaeological data, it does not seem reasonable today to propose that only pottery was adopted from Eurasia, while population was exported.
Also, EHG ancestry appears between ANE and WHG in PCA, and has been thought to be a mixture of them – although this model does not fit with the current data[Haak et al. 2015]. If EHG was in fact a combination of both WHG and ANE components, the EHG > ANE cline observed in eastern European samples in the transition from the Mesolithic to the Eneolithic may be explained by multiple contributions of populations with high ANE component. That would account for different Mesolithic invasions of R1a-M420 subclades (of ANE ancestry) from central Eurasia into an eastern Europe dominated by R1b-M343 lineages of WHG ancestry.
Diachronic map of Palaeolithic migrations.
Diachronic map of Mesolithic migrations in Europe ca. 6500-5000 BC [Anthony 2007][Piezonka 2015], Uni-Köln.
Diachronic map of Mesolithic migrations in Asia ca. 6500-5000 BC.
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