It looks like the current learned opinion is that
"blues scale(s)" are an African-American innovation. Acc. to James Lincoln Collier in the New Grove Dictionary of Jazz, 2nd ed.:

"[West African music] used scales roughly similar to European ones, but they tended to be pentatonic and seem to have avoided half-steps, either by skipping over them or by the raising or lowering of one of the pitches to widen the interval; pitches were frequently inexact by the standards of European music....

"[J]ust as some African tribal musicians seem to have avoided half-steps, so the slaves tended to adjust the diatonic scale to similar effect by lowering the third, seventh, and sometimes fifth scale degrees microtonally, thereby creating the so-called blue note...."

I assume this means that nobody found blue notes in Africa before the advent of commercial blues-playing radio. That would have been well into the anthropologically sophisticated 20th C., so if nobody noticed them it would be strong, though not conclusive, evidence for an American origin.