started in the early '70s on the streets of the West Bronx, it was a combination of doing "dozens"
and speaking the lyrics of reggae
songs over the beats (a few early rappers were Jamaican
immigrants, and this was a bit before reggae had spread to the US).
At parties the djs began rapping and spinning records
. From Davey D's History of Hip Hop
"In those early days, young party goers initially recited popular phrases and used the slang of the day. For example, it was fashionable for dj to acknowledge people who were in attendance at a party.
Criticizing rap music
As this phenomenon evolved, the party shouts became more elaborate as dj in an effort to be different, began to incorporate little rhymes-'Davey D is in the house/An he'll turn it out without a doubt.' It wasn't long before people began drawing upon outdated dozens and school yard rhymes. Many would add a little twist and customize these rhymes to make them suitable for the party environment. At that time rap was not yet known as 'rap' but called 'emceeing'."
for being self referential
is like criticizing European classical music
for using violins