The blues is widely misunderstood.

This is partly because a lot of people, for a long time, have wanted to believe that there was something very authentic and pure about rural Southern blues forms, that they reflected a pre-modern time period before the world was tainted by consumerism and modern capitalism. They have wanted to believe that these rural Southern blues forms are the forms that jazz ultimately derives from. This is the story told, for example, in the influential 1938 John Hammond-curated concert From Spirituals To Swing, which presented a chronological history of African-American musical forms, from spirituals to blues to ragtime to swing. Hammond enthusiastically reviewed the Delta blues musician Robert Johnson in the lefty press, and was very disappointed to find out, when trying to book Robert Johnson for the concert, that he had died relatively recently.

In the 1960s, the white rock'n'rollers who wanted to find the purest form of the music they loved, making some problematic assumptions about the music and the black musicians who originally made it. They gravitated first to the Chicago blues style of Muddy Waters, B.B. King, John Lee Hooker and Howlin' Wolf. Before long, they then found one of the major influences on much of the Chicago blues style, the Delta blues of the 1920s-1930s (where many of the Chicago blues musicians had grown up before moving North as part of the Great Migration.) Musicians like Bob Dylan or Keith Richards of the Rolling Stones in their biographies recall being spellbound hearing the acoustic blues of Robert Johnson for the first time - they felt like they had hit the source of their music, the sound they were searching for in its purest form.

This idea of the purity and the authenticity and the historical important of the blues is deeply engrained in much of the discourse around the blues, and is partly why many jazz histories feel obligated to include a section on the blues early on, which they also use to demonstrate the African-American authenticity of jazz (a genre which has always been profoundly uneasy about the role of race in its meta-story, given the troubled race relations in the US).

There is a specific story told by W.C. Handy, a (black) musician, and author of 'Beale Street Blues', 'St. Louis Blues', and 'Memphis Blues' about hearing a black musician playing a guitar in the Mississippi Delta, and how that inspired the 'St. Louis Blues' and his subsequent musical direction. However, W.C. Handy, when he heard this mysterious black musician, was a classically trained ragtime musician who played in minstrel shows, and his compositions sound like it to modern ears. And there's suggestions the story was apocryphal anyway, and that Handy was merely following pre-existing trends. But given Handy's prominence and his role in early jazz (many of the New Orleans jazz groups played his compositions, turning them into jazz standards), the link between the Delta blues and subsequent African-American musical forms was established.

However, the idea that the Delta blues represents a sort of living fossil that has survived as the music evolved from slave songs to jazz and rock'n'roll...it's a very problematic idea. It may well be that the Delta blues of the 1920s was radically different from the music that W.C. Handy heard around the turn of the century. 20 years is a long time, and this was plenty of time for music to fall in and out of fashion - after all, to use a more modern example, there's been some major changes in sound between Public Enemy and Drake, but both are apparently hip-hop. Just because the music that happened in between was not recorded doesn't mean that it wasn't subject to fashion - these were people who lived in a dynamic, competitive capitalist world, not some unchanging rural utopia.

Firstly, one big problem with the argument that the blues genre has 'its origin in American slave songs' is the fact that there were no American slaves after the 1860s, what with their emancipation (though, sadly, in some ways the lives of many African Americans did not change very much after emancipation, thanks to Jim Crow laws and the sharecropping system that replaced slavery). Additionally, descriptions of American slave songs from before the 1860s are almost uniformly descriptions made by white people - visitors to plantations, or children of plantations. Those who enslaved them were almost wholly uninterested in the musical features of slave work songs, and usually did not have the technical musicological skill to describe the music very accurately, almost always focusing on the words or the impression it left them with. Furthermore, slaves were not permitted freedom of movement, and came from a great many different cultural backgrounds; it might be that slave songs differed very greatly on different plantations. All of this means that we really don't know much about slave songs. We might perhaps see something closer to slave songs in the minstrel songs of the 19th century, where white people put on blackface, and gleefully enacted particularly offensive stereotypes. But it's impossible to figure out how much of minstrelsy was based on relatively accurate mimicry of what white people heard as they idly looked out on black people doing backbreaking work, and to what extent minstrelsy transplanted some tokenistic musical features from African-American music onto pre-existing white folk forms.

In addition, even after the advent of recordings around the turn of the 20th century, basically nobody bothered to make recordings the 'ethnic music' of rural Southern African-Americans until the mid-1920s, over half a century since the end of slavery. While there may well be influences of slave songs on the acoustic blues music that did start to get recorded in this period, the people playing that music in the 1920s lived in a changing world, and their music very much reflected this. One indication of this, for example, was that the rural music recorded in the 1920s is largely played on acoustic guitars in a Spanish style, an instrument that had permeated the rural South thanks to, for example, the Sears catalogue; this was a relatively new development in the music, seemingly, displacing more African-influenced instruments like the banjo.

Additionally, there is every indication that the musicians of the rural South who were recorded by the record companies of the 1920s had a much broader repertoire than what they were recorded as playing. Many of them were working musicians who played an assortment of music that would please a diverse set of audiences, and that included everything from ragtime, to minstrel songs, to the popular songs of the day, to what we'd now recognise as 'the Delta blues'. There's also lots of indications that a lot of blues songs were made up on the spot, more or less, by the musicians - those recording the music wanted novelty - new things they could sell that were unlike the old things that consumers didn't want any more. And so the easiest way to give the record companies what they wanted (and thus make more money) was to make up something new; so many blues songs were indeed something new, rather than salvos from a pre-consumerist era. And so the desires of the recording companies shaped what came to be known as the rural blues just as much as the repertoires of the rural folk musicians they recorded. All of this, for better or worse, profoundly informs the seemingly 'primitive' rural acoustic blues of the Mississippi Delta that is often seen as the exemplar of the earliest form of the blues.

All of this also means that the blues is intrinsically an American music, rather than a lightly changed native African music. African cultures have different scales of notes; the 'blue note' of blues music and jazz, bent or slurred on instruments or singing so that it sits somewhere between a major and a minor third, perhaps reflects attempts to express African musical features on European instruments. As such, the act of playing a blues note on a European instrument like a guitar transforms the meaning of the note.

In addition, it is profoundly difficult to identify cultural traditions from modern west African cultures which 'map onto' the blues. West African cultures were just as profoundly changed by the slave trade as the African-American culture that developed on the other side of the Atlantic, and they are not unchanging monoliths where you can directly detect cultural influence.

With all of that said, as the example of the blue note above suggests, there are certainly features of blues and jazz which are profoundly unusual in the context of other American musics, and for which you would have to assume some sort of African origin - the blue note, the way that syncopation is used within the music, the focus on rhythm. Many of these musical features are perhaps best seen as amalgamations of the musical features of a variety of African cultures as people from different cultures found themselves together, attempting to communicate, in between being whipped by white people who didn't really want them communicating.

Sources: Elijah Wald's Escaping The Delta, Marybeth Hamilton's In Search of The Blues, Ted Gioia's Delta Blues, Jack Hamilton's Just Around Midnight, etc