Hancock does not posit globespanning civilizations, but rather far-flung refugees. Any actual globe-spanning civilization would have left plentiful traces where

Hancock does not posit globespanning civilizations, but rather far-flung refugees. Any actual globe-spanning civilization would have left plentiful traces where they could still be seen, so that seems ruled out. Washing up in Iraq, India, Mexico, and Peru would be more consistent with a single origin in southeast Asia than in the Atlantic, but a global cataclysm ought to produce refugees from multiple places. Any genetic signal of scattered refugees would be faint.