Ten years ago in 2015 the first ancient DNA from Yamnaya archaeological culture was published in Haak et al. study. The discovery of R1b-Z2103 in Yamnaya was a big sensation given that many commentators were expecting a R1a there, who's correlation with IE languages spread was self evident back then.
Last year Lazaridis et al. 2024 has virtually solved the origins of Yamnaya autosomes. Yet the exact origin of it's main Y DNA, the Z2103 remains unsolved. Yediay 2024 addressed this issue ( picture 2) noting that virtually all known cases of Z2103 found in Eurasian steppe are Z2106+ while all known cases of Z2103+ are found in ancient South Caucasus.
How to solve this contradiction?
In the current stage of our knowledge we know that Z2103 had a dramatic founder effect with the spread of Yamnaya culture and was practically absent in Pontic Caspian steppe before the advent of that culture at 3300BC. As consequence of this 41 out of 51 Y DNA extracted from Yamnaya are Z2103 positive (more than 80 percent) . So the real homeland of Z2103 must be in the same place as the start of Yamnaya. Yamnaya autosomes are largely derived from the preceding CLV (Caucasus Lower Volga) cline, genetically the closest sample was from near Azov region (Krivianskiy). But in addition to CLV they had also extra Ukraine Neolithic Hunter Gatherer ancestry and some Caucasian farmer related ancestry. This two facts are restricting the potential homelands drastically. Previously we have seen an infiltration of of UNHG in to Krasnodar region of Russia while the extra Caucasian farmer related ancestry was present in the same region also. Based on this it's safe to assume that Z2103 started it's expansion somewhere between Azov and Caucasus regions. This homeland explains multiple issues.
+ The reason why all three Z2103* branches (Y4362, L584, PF331) are found in West Asia. The proximity to Caucasus resulted to their migration to south.
+ Z2106 also might have formed near Caucasus. It's main subbranch R-Y503415 was found both in south Caucasus and north of it.
+ An initial spread from west to east also explain why the Afanasievo culture appears practically simultaneously with Yamnaya in Altai region. Most of Afanasievo culture males are positive to Z2108, a rare subclade found today in China. Some of Z2108 remain in Pontic Caspian steppe where a subclade KMS67 expands.
+ And finally after filling all the Pontic Caspian steppe with their settlements Yamnaya move to Balkans where the subbranch Z2110 is found. Despite this in Balkans the most successful founder effect is attested in J2b2a-L283 another minor Yamnaya lineage originated from south Caucasian farmers.
Even though this rule is not universal but a potential homeland must be also the source of more diverse cultures. Near Krasnodar region we see two other archaeological cultures related to Yamnaya. The Novotitorovka and North Caucasus. The Novotitorovka is remarkable because it yielded numerous wagons similar to those found in Lchashen in Armenia. Which further raises the probability that its exactly in that region that we must expect to find Y DNA ancestral to those found in West Asia, including the elusive I2a2b.
