THE BLUES
(circa 1865)
After the civil war, the newly freed people had a whole new kind of trouble to deal with. They were taken from the lives that they had known and thrust into a new world that, while it had freed them, wanted nothing to do with them. The American culture could no longer condone the blight of slavery, but niether was it ready to accept the new free men and women into their society. 
To those who did not find a new kind of slavery in the rentee/landlord arrangement with landowners, this introduced a new kind of transitory lifestyle to many, especially men. It was these men who took up both guitar and harmonica, instruments that were cheap and easy to travel with. It was in this setting of displacement in their own country, that the blues were born from their souls.
What made the Blues so different, beyond the inherent sense of frustration and despair that so many Afro-Americans felt at that time, was the legacy of the worksong. The early blues artists and even the later Jazz musicians used their instruments as extensions of their voice. The rythyms that they made were in the same non-syncopated form as the worksong had been and the sounds were meant to mimic the human voice. It was this way that the blues became even more poignant and even more sucessful in their intent to convey emotion.
Traveling Blues shows, Minstrelsies, began to tour the country. Blues began to be heard everywhere, and it began to influence people if only to prepare them for what came next. It was still primarily black music listened to by black people, but that would change.
JAZZ
(circa 1900)
Around 1914 the great exodus north began. WWI was a major catalyst in producing the modern black man. It was through this internationality that Afro-Americans were able to see the world as more of a whole and their place as Americans within it. They participated in the war (albeit in their own segregated troops) and while they were meant to simply be more bodies to use in the war-machine, they gained an enormous sense of being part of something....that something being America. And so they began to try and step up into the role of American, not just ex-slave.
Afro-Americans were drawn for many reasons to the industrial centers of the north(mainly St. Louis and Chicago). One of the biggest was simply the need to leave behind the south and the slavery it was associated with. There was also the call of work, work that was not simply agricultural. The American dream was drawing these particular Americans forth as much as it did with the early pioneers of the West. Up the river went the Blues and a new kind of music went with it.
During the reign of Napoleon, the military band was all the rage among the French. This translated to the importation of brass band instruments to all the french settlements, New Orleans included. Creoles ("mixed breeds"- usually part black,part french, sometimes part indian) who were usually well educated freemen, and later their newly freed bretheren, became infatuated with these instruments and the sounds they could make. Incorporating the sounds of blues and the same non-western, non-syncopated rythyms that had been brought from Africa, a new breed of music began to grow. At first it was simply a take on traditional marching band music, but it began to metamorphize as blues became more and more prevalent. First Ragtime, and then Jass, or Jazz. Again, the instrument was employed to mimic the human voice in tonality and spirit, and again, something wonderful emerged.
From New Orleans, Jazz moved upriver with the exodus and in the house-parties of the 20' and 30's, it gained momentum. Where the Blues was the "devil's music" to many of the Black middle class, Jazz was acceptable. "Black music" was the rage in the clubs and parties of the 20's. Jazz made it possible for Afro-American music to be imitated for the first time by white musicians...the beginnings of what was to come. The broad emotional meaning of the genre allowed such cross-cultural developments without being 'watered down'. From Jazz grew many different elements within it. Bebop, Swing, Boogie Woogie, Free Jazz and Hard Bop were all examples of the experimentation the musicians of the time were making to elevate the sound. It became more and more mainstream and more and more musicians began to try new things...to take things another step along.
RHYTHM & BLUES
(circa 1940)
Nothing shaped modern day Rock and Roll more than Rhythm & Blues. It was first and foremost a backlash against the direction that Jazz had gone. As with anything adopted by the masses, Jazz had lost its soul in many respects. It was to undergo a revival...looking back to the older blues heart of it, but the musicians of the time were looking for something new. Out of the Hard Bop movement within Jazz itself, the innovators added a new funky backbone..getting harder with the rythyms and the sounds. The soulful feel of Gospel blended in to produce the next step in the evolution of black music. It became again, an almost exclusively black music...but not for very long. The radio began to blare these "shouting blues" and again it was taken up by the mainstream. Now you can listen to almost any modern rock today and you will hear the soul roots of the Rythym & Blues pioneers.
FUNK
(circa 1970)
Funk took its name from a black slang expression meaning body odor, but it wouldn't wear off as the '70s wore on. It lasted at least 15 years, leaving a collection of work as durable and as danceable as anything ever produced. Funk referred most to the strong bass line, and it became the movement where R&B's anonymous studio legends of the '60s 
came out from behind the slick vocal groups to become stars. Funk used the upped volume from the late 60s rock bands and turned R&B eclectic. Funk was street music and it was drug music, it was the experiment with R&B that took on its own life. The evolving social climate was not being addressed by many of the major labels and the artists felt the need to express those changing times. Artists like George Clinton, Curtis Mayfield, and James Brown were getting down and dirty. The 70s were as much an effort to take it to the next level as it was a rebellion against the polish of the formulaic '60s R&B. Funk was sex, drugs and Rock n' Roll at its ultimate.
HIP HOP/RAP
(circa 1978)
The nationwide popularity of Rock n' Roll was pervasive and complete. It had permeated every layer of American culture...and not only was it stagnating in some respects, it was also losing the voice of the Afro-American who had created and fueled it. Funk's sound and rythyms did not evolve into Hip Hop, but it did set the stage. There are several elements to Hip Hop, which were defined in the streets during the late '70s... rapping, DJing, break dancing and graffiti writing. Hip Hop was and still is its own sub culture, and that culture had its own voice.
The times were changing again and Afro-Americans had yet another new set of problems to deal with as the nation progressed. The migratory steps that had been taken since the beginning of the century had led many of America's blacks to the citys, and early on, their boundaries in society had been set as surely as any chain around the neck. Confined to certain areas of the city, relegated to jobs with little to no wages, a pattern was set that assured poverty and with it, poor education. Up to this very day, this is the case, and the black man had a new set of blues to sing.
Rap is the closest road that black music has taken back to its original roots in the worksong. The "Call & Response", the rhythmical use of the voice as an instrument, and the deep seated frustration inherent in the environment are all present. Drawing up the R&B rhythyms and "rapping" over it grew out of the house party and the clubs just as Jazz had. In 1979, FatBack released "King Tim III", the SugarHill Gang released "Rapper's Delight"... and a new genre was born.
The evolution of black music is simply the evolution of American music. It is also a definitive paralell with the history of the Afro-American in America. It speaks clearly of the feelings and thoughts of a people who had to exist within a society and yet still be forced to remain seperate from it. When you talk about black music, you are talking about Afro-American history.
Before Rap, before R&B, before Jazz and before Blues... there was the Work Song. None of the musical genres that came after these work songs could have existed without them. The "Call & Response" form of these worksongs came straight out of the Slaves' African heritage. Originally, they were ritualistic in nature and related directly to the religions they had left behind. The only instrument they used was the drum and their own voices. It was 
not long after they arrived in America, however, that they were not allowed to either sing in their native tongue, nor put anything related to their religion in the lyrics. The drums were believed to incite rebellion and they were taken away. And so the slaves began to merge the tone and rhythm of their old language into the chant and the lyrics were derived directly from their everyday life. The voice became used as an instrument and set the scene for what was to come.
Interestingly it was the Quakers who put a twist on the dilema and claimed that converting the slave to Christianity was a justification for slavery. As Afro-Americans were allowed religion, it became a unifying social occasion. Something for them to rally around and believe in. Up until this point, they had not been allowed to practice any kind of religion at all, except furtively. Now they could gather, socialize and in a sense, elevate their spirits. 
Gospel grew out of this as singing became a natural outlet for their pent up frustrations and troubles. The same "Call & Response" of the worksong was utilized and expounded