One Origin for Everything
Professional anthropology rejected the theory by the 1930s, but it is the direct ancestor of modern lost-civilisation writing. Its underlying premise — that most peoples could not have independently invented their own monuments — is worth naming plainly as the flawed assumption it rests on.
Grafton Elliot Smith, The Migrations of Early Culture (1915); Thor Heyerdahl's Kon-Tiki voyage (1947), reviving contact arguments
An early-twentieth-century theory that all world civilisations descended from a single ancient Egyptian source, since abandoned by scholars.