"The west-to-east gene flow that began after the 4300-4200 BC collapse could have continued into the Yamnayaperiod. Part of the WHG that Wang et al. (2018) detected inYamnaya genomes could have been picked up in the Dniepervalley, where many Dnieper-Donets individuals had WHGancestry, possibly lessening the necessity for mate exchangeswith Globular Amphorae. Probably, late PIE (Yamnaya) evolved in the same part ofthe steppes—the Volga-Caucasus steppes between the lowerDon, the lower and middle Volga, and the North Caucasuspiedmont—where early PIE evolved, and where appropriateEHG/CHG admixtures and Y-chromosome haplogroups wereseen already in the Eneolithic (without Anatolian Farmer).There have always been archaeologists who argued for anorigin of Yamnaya in the Volga steppes, including Gimbutas(1963), Merpert (1974), and recently Morgunova (2014), whoargued that this was where Repin-type ceramics, an importantearly Yamnaya pottery type, first appeared in dated contextsbefore Yamnaya, about 3600 BC. The genetic evidence isconsistent with Yamnaya EHG/CHG origins in the VolgaCaucasus steppes. Also, if contact with the Maikop culture wasa fundamental cause of the innovations in transport andmetallurgy that defined the Yamnaya culture, then the lowerDon-North Caucasus-lower Volga steppes, closest to the NorthCaucasus, would be where the earliest phase is expected."
" I would still guess that the Darkveti-Meshoko culture andits descendant Maikop culture established the linguisticancestor of the Northwest Caucasian languages inapproximately the region where they remained. I also acceptthe general consensus that the appearance of the hierarchicalMaikop culture about 3600 BC had profound effects on preYamnaya and early Yamnaya steppe cultures. Yamnayametallurgy borrowed from the Maikop culture two-sided molds,tanged daggers, cast shaft hole axes with a single blade, andarsenical copper. Wheeled vehicles might have entered thesteppes through Maikop, revolutionizing steppe economies andmaking Yamnaya pastoral nomadism possible after 3300 BC. So it is still possible that steppe people interacted asraiders and traders and perhaps even political clients of theMaikop people, with interaction intense enough to makeleading political figures in the pre-Yamnaya steppes bilingual inthe Maikop (Northwest Caucasian?) language. Some Maikopwomen might also have become the wives of some preYamnaya men. If their speech was copied by others aroundthem, the linguistic exchanges and interferences suggested byBomhard could have occurred and spread without an equallylarge exchange of mates. But if the interpretations presentedhere are supported, mate exchanges between Maikop and preYamnaya or Yamnaya people were few in number, rare infrequency, and when they did happen, involved primarilyMaikop women, not men. If more mating had occurred, wewould see more EHG among the Maikop genomes and moreAnatolian Farmer among Yamnaya steppe genomes than we dosee. Of course another, final, possibility, consistent with thearchaeological and genetic evidence presented here, is thatthere were two phases of interference from Caucasianlanguages in two periods. The first, perhaps responsible forsome of the basic morphological and phonological traitsBomhard detected, could have occurred in the fifth millenniumBC and involved very archaic eastern Caucasian languages thathad moved to the lower Volga steppes with CHG people, wherethey intermarried with Samara-based EHG pre-Uralic people tocreate early PIE and the Khvalynsk culture and a newEHG/CHG genetic admixture; and the second phase, which left a Northwest Caucasian imprint over late PIE, perhaps moresuperficial (lexical) than the earlier interference, could havebeen during the Maikop period, but without a major geneticexchange between Maikop and Yamnaya."