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Were mtDNA H2a1, I, R1a and W the haplogroups of the Maykop culture ?
The North Caucasus has a very unique genetic landscape. The mitochondrial haplogroups found there, especially in the Northwest Caucasus include a lot of rare lineages that aren't found at higher frequencies almost anywhere else. These include haplogroups H2a1, I (mostly the I1, I2 and I4a subclades), R1a (not to be confused with its Y-DNA homophone), U2e and W. There are also other more common haplogroups that reach unusually high frequencies in parts of the Caucasus, such as K, U3 and X2, although they probably originated in the South Caucasus and the Near East.
What piqued my interest is that haplogroups H2a1, I and W in particular (R1a being so rare anyway) have never been found in Europe nor in the Near East before the Bronze Age. That made me wonder where they could have originated. If they weren't native to Europe, nor from the Near East, and they aren't East Asian or South Asian either, that only leaves the North Caucasus, a small region that was isolated from the South Caucasus, Anatolia and the Fertile Crescent by quasi-impassable mountains: the Greater Caucasus range, a formidable natural barrier of snowy peaks exceeding 4,000 or 5,000 metres on most of its length. It is therefore not surprising that many lineages, and particularly the less mobile ones on the maternal side, should have evolved in relative isolation for many millennia probably since well before the end of the last glaciation.
It could be that the lineages that ended up stuck against the northern edge of the Caucasus once roamed the Eurasian steppes as nomadic hunter-gatherers, and that they were force to migrate south during the Last Glacial Maximum, only to find their way blocked by the Caucasus, and so they settled there. Haplogroups H2a1, I, U2e and W are also quite common in the eastern Baltic, so the traditional territory of these lineages might have spanned between the Baltic and the North Caucasus. Whether the Palaeolithic paternal lineage associated with them is R1a or another (extinct ?) haplogroup is yet to be determined.
What is interesting is that H2a1, I and W are now found dispersed around most of Europe, the Middle East, Central Asia and North Asia. All of them correlate pretty well with the distribution of Y-haplogroup R1a. Yet, none of them were found in Eastern Europe, even in Russia, before the Bronze Age. This may just be due to the scarcity of ancient DNA samples. But there are over 30 Mesolithic Russian samples and all of them belonged to H, T, U2, U4 or U5.
H2a1, I and W then all suddenly show up in both the Corded Ware and the Unetice culture in Central Europe during the Bronze Age. This makes me wonder whether they were original R1a lineages from the forest-steppe, or if they represent an ingression of Northwest Caucasian people (Maykop culture) into the R1a steppe population.