and 3300, substantial contact took place between the steppe cultures and Mesopotamia via the Maikop culture (3700–3000 BCE), in the northern Caucasus. To the west, Tripolye pottery begins to resemble Sredni Stog pottery, showing a process of assimilation between the Tripolye culture and the steppe cultures and a gradual breakdown of the cultural border between the two. Between 3800 and 3300 BCE, five eneolithic steppe cultures can be discerned, and Proto-Indo-European dialects may have then served as a regional language. Mikhaylovka culture (3600—3000 BCE), on the Black Sea coast between the Dniestr and the Dniepr. Mikhailovka I people looked less like the Suvorovo-Novodanilovka people and may have intermarried more with Tripolye culture people or people from the Danube valley. Mikhailovka II upper level (3300–3000 BCE) imported pottery from the Repin culture (see below) and is regarded as early western Yamna. In the steppes northwest of the Black Sea l, the Mikhailovka culture was replaced by the Usatovo culture after 3300 BCE. The Mikhailovka culture at the Crimea developed into the Kemi Oba culture. Post-Mariupol culture (early phase 3800–3300 BCE, late phase 3300–2800 BCE): around the Dnieper Rapids, near the Donets River. According to Ina Potekhina, the people looked most like the Suvorovo-Novodanilovka people. Late/Phase II Sredny Stog culture (Dniepr-Donets-Don), c. 4000–3500 BCE. Repin culture (Don) and late Khvalynsk culture (lower Volga): the Repin culture developed by contact with the late Maikop-Novosvobodyana culture (Lower Don), which penetrated deeply into the Lower Volga steppe. Anthony also believes that Repin was highly significant to the establishment of the Afanasevo culture in eastern Siberia, c. 3700–3300 BCE. Chapter Thirteen: Wagon Dwellers of the Steppes. The Speakers of Proto-Indo-European The Yamna horizon (3300–2500 BCE) originated in the Don-Volga area, where it was preceded by the Middle Volga's Khvalynsk culture (4700–3800 BCE) and the Don-based Repin culture (ca.3950–3300 BCE), and late pottery from these two cultures can barely be distinguished from early Yamna pottery. The Afanasevo culture, at the western Altai Mountains, at the far eastern end of the steppes, was an offshoot from the Repin culture. The Yamna horizon was an adaptation to a climate change between 3500 and 3000 BCE. The steppes became drier and cooler, herds needed to be moved frequently to feed them sufficiently, which was made possible by the use of wagons and horseback riding, leading to "a new, more mobile form of pastoralism." It was accompanied by new social rules