The modern theory of migration, or borrowing, according to which the individual myths originate from definite peoples [especially the Babylonians], and are accepted by other peoples through oral tradition [commerce and traffic], or through literary influences.
Rank identifies and critiques the diffusionist ‘migration and borrowing’ theory of myth distribution, arguing it is merely a modification of earlier source-theorizing inadequate to the universality of mythic structures.
, The Myth of the Birth of the Hero, 1909thesis