Over the recent decade, abstracts of many thousands of folktales recorded in Europe and Asia have been added to our Electronic Catalogue of World Mythology and Folklore. Their analysis reveals systematic parallels between the traditions of Western Eurasia and America, those of the Plains Indians in particular. Such motifs are especially apparent in Ancient Greek mythology (Phaethon’s fall, Pasiphae and the bull, cranes attacking dwarfs, etc.). Although they have been known since the 19th century, no explanation for them could be proposed for a long time. The situation changed thanks to recent advances in Siberian paleogenetics. Before the peak of the Last Glacial Maximum, Eastern Siberian populations (Yana RHS and Malta) exhibited European affinities. By the mid-Holocene, population replacement occurred. It was not abrupt, but eventually resulted in a breakup of the initial cultural continuum spanning the Eurasian boreal zone and later extending to the New World. Many of the Western Eurasian–American motifs are episodes from stories of adventures. On the other hand, parallels between traditions of the Indo-Pacific rim of Asia and America mostly relate to motifs that are mythological in the narrow sense (etiological and cosmological), including early ones, evidently stemming from Africa. From the Hunno-Sarmatian, if not Scythian age onward, Southern Siberian and Central Asian motifs had been transferred to Western Eurasia on a large scale. Classical sources mirror an earlier stage of European mythology, hence the difference between the Ancient Greek set of motifs and that peculiar to later European traditions.