E
elmanito
Wind can indeed explain expansion, but let's not forget birds and why not also hunters-gatherers who, we can imagine, would have collected and stored the seeds for food use during their nomadism, sometimes unwillingly (or not ?) sowing a few seeds here and there, migration after migration, generations after generations. This is only a supposition of mine, but I don't think it is eccentric.
Its possible especially birds, but so far as i know humans began to eat seeds when they started to grow crops.We do know that we gathered berries,mushrooms, caught fish and wild animals like mammoths, but no seeds.Archaeologists have found hemp seeds in graves in the Altai-mountains and not in graves in Europe.
Namaste