In the times of slavery slaves would sing call and response songs in the slave pens which turned into Blues, Jazz Swing, and R&B such as Louis Armstrong and Ray Charles. Louis Armstrong made Jazz more of a solo kind of style instead of in orchestras. The blues music was from bad happenings in their lives and from the slavery. Jazz was a style with a rythm that moved more and swing was more crazy and out of control. Scat singing was a wordless singing style which was for rythm. In the ghetto after the slavery but during the descrimination people only had their voices and objects around them for making music. Rap was a spoken type of music influenced by scat singing. Rap was poetry syncronized with an instrument with a quick, short sound to give it sync with the syllables of words. In the ghetto they probably used trashcans. In the 70's people had used the technique of "scratching" with records. In the 80's came Run-D.M.C. who used scratching, drums, and used guitarists in some songs came and pretty much created rap for what it was by definition: poetry in motion, and poetry has rhyme scheme or meter but rap follows both of those. In the 90's there were rappers like Tupac and Notorious B.I.G. who would rap about the streets. These rappers used beatboxes, and beatboxes still had the quick, short beat that fit rap.
At the turn of the millenium, after Tupac and Notorious B.I.G.'s deaths. Rappers were following the theme that they set, the problem with these rappers were: they acted too egotistic and rap became all about money and image. And to look richer more rappers used synthesizers in their music. Synthesizers, have a more constant beat, not the quick short one that fits rap. Also the poetry was dropping too, and rap is "poetry in motion" so what is called rap these days isn't even rap.
My opinion on modern rap and modern rappers
Modern rap sucks ass! Half the modern rappers aren't from the streets and to make it look like they are, they have to rap about the streets which they know nothing about. Modern rappers also rap about image. A modern rap song sounds like "everybody likes me, look at my shoes" and shit like that. The thing is nobody likes them. There aren't as many rap fans as there used to be, even the wiggers don't listen much to modern rap. Some rapper/rap group better come along with poetic meter and rhyme and the good sync of drums with syllables. And not sound like a repetetive dipshit(s) that only know(s) two words.
intelligent person: I prefer to listen to good rap like Run-D.M.C., not dumbasses like chamillionare who mispronounce words to try and make them rhyme because they don't know how to rhyme.