“No migrations are required to derive the attested IE distribution from a reconstructed homeland consisting of a locus in western central Asia and a range over the steppe and desert. Sometime in the fourth to early third millennium, PIE spread along the steppe and southern trajectories to occupy the entire reconstructed range: the steppe, the desert of wester central Asia, part of the adjacent mountains, and perhaps some of south- west Asia. At this time its distribution was continuous, and that distribution had been achieved not by migration but by expansion.”
JN