Scythians emerged from substantial genetic turnovers replacing homogeneous Bronze Age herders. Iron Age nomads drew from eastern Altai source spreading west into Saka, Tasmola, Pazyryk cultures. Western Ural Sauromatian-Sarmatian groups stemmed from separate simultaneous source and stayed consistent during westward expansion. Scythian decline coincided with new far eastern Eurasian influx from Xiongnu and Xianbei. Minor Iranian influxes linked to Persian expansions contributed to Scythian replacement. At least two main origins for nomadic Iron Age steppe groups. Admixture from east, west, south formed new gene pools around first millennium BCE. Earliest Scythian burials in Altai match genetic expansion timing. Populations of Eurasia repeatedly changed and intermixed over time. Study analyzed 111 ancient genomes from Central Asian steppe cultures.