In brief: Rex Harris carefully sets out the following general theory of the origin of "jazz" in his book, Jazz:
Slavery in the US completely erased African culture. "Jazz" originated from the resulting blank slate. It did not originate in other slave holding areas because those areas allowed for more African cultural expression.
This seems like an innocent enough claim, and sounds so familiar as to be nearly aphoristic. But the general thesis also lays the groundwork for Harris's fetishizing of the rough, raw, untutored, masculine, artless, nearly "savage" Black Man, who is the ideal practitioner of the only phase of the music's history Harris acknowledges as "Real Jazz." (Roughly, 1918-1938 or so). It's a double edged sword, because he does a certain justice to the outrage and inhumanity and reality of slavery, yet seems to use this same historical reality to develop an essentially racist (no matter how "positive") musicology.
This seems such a reflection of the history of people writing about the music. One reason I find Harris's book so fascinating is it's more than 50 years old, yet echoes many of the tropes encountered in current and intervening "jazz" writing. "The problem of slavery" is always dealt with in some way or another, as is "the problem of technique" and "the problem of education" and "the problem of improvisation." It's usually a fairly easy matter to uncover the bias behind a theory of the origination of improvisation as an art form born out of ignorance, necessity and a sort of romanticized/fetishized primal stupidity.