Do we know how this region was populated and the movements it has seen?

This region has a lot of steppe admixture in most models. Do we know if this was mediated by Yamnaya, Catacomb, Steppe Iranians, Slavs? They also have appreciable frequencies of y I, R1a and R1b. Some groups are bottlenecked with G and some groups with high steppe have little R1. Was this region mostly CHG before the admixture of EHG? Did they receive any Iran_N, Anatolia_N, Levant_N admixture?