James Brown's rhythm's were a huge influence

All of the above had seeped into the consciousness of a young New Yorker who called himself Kool Herc, who during the 1970s began reciting rhymes over the instrumental parts of the records he was spinning.

'Scratching'

With two turntables going and two copies of each record he could play the break over and over while he rapped.

Many feel Kool Herc was the true originator of rap.

Grandmaster Flash's Adventures On The Wheels Of Steel in 1981 added a new element - the exhilarating collage effect of "scratching" different records together to create a new whole.

With disco and rock's new wave starting to sound tired, rap's directness and apparent street authenticity were invigorating.

Like punk before it, rap polarised music fans - but even its proponents would not have predicted that rap would become a 20 year-old fixture on the music scene.

Mythology

This year, rap even overtook country music as Americas' second favourite style - after rock.

Like other styles of pop music, rap had its own dances - breakdancing and bodypopping - its own clothes, and its own mythology.

The mythology of rap became increasingly important, repelling and attracting fans in equal measure.

Rap was proud of its origins in the black ghettos of North America, and spoke of poverty, police brutality and defiance.

It also, some said, celebrated a violent machismo and mindless materialism.

Certainly, once the first wave of rap artists had come and gone - including Afrika Bambaataa, Run DMC and Roxanne - the was a something of a lyrical vacuum in which "gangsta" rap found it easy to get attention.

Nihilism

It was on the West Coast of the US in the late 1980s - far away from rap's origins in New York - that gangsta rap took hold, notably in the work of Ice-T and the group Niggas With Attitude.

Coolio: Gangsta rap with a conscience

As if in response to such nihilism, the group Public Enemy promoted a serious black separatist political agenda - to find themselves with a huge number of white European fans.

At the same time, De La Soul expressed a wry, witty side of rap which many fans found much more user-friendly.

But rap's bad image would not go away - or could not, given the behaviour of some rap artists.

In September 1996 Snoop Doggy Dogg was acquitted on a murder charge, just before another rapper, Tupac Shakur was murdered in a shooting.

In 1997 rap label boss Suge Knight was sentenced to nine years in prison for a range of offences, and in March of that year the Notorious BIG (aka Biggie Smalls) was murdered.

More positively, rap was becoming a medium for the world's youth to express themselves, not only in Anglophone countries but in France (notably with MC Solaar), Germany (Rammstein), Finland (Bomfunk MCs), Japan (Muro) and the Czech Republic (Chaozz).

Established

Even communist Cuba was not immune: the Orishas, based in Paris, took their brand of Salsa rap to Havana earlier this year.

Towards the end of the century rap was clearly established as a force in its own right, no longer a sub-section of black music or dance music.

At the same time it was also noticeable that the lines between rap and other forms of pop music were becoming blurred - who could say where, exactly, rap stopped and RnB or Dancehall began?

The music had also matured to the point where a white rapper, Eminem, could combine authenticity with crossover appeal and become one of the world's major music stars.

The protégée of producer Dr Dre, Eminem has aroused just the same shock and controversy that rap artists have always done in the last two decades.

Congress

But there are now serious shadows on rap's horizon.

Members of the US Congress are talking about legislation to penalise record companies who market obscene records to minors.

And opposition to the imagery of violence and misogyny that characterises at least some rap has widened to include black organisations like the National Political Congress of Black Women.

So it is a sober atmosphere in which this week's hip hop summit has taken place.

And it is not surprising that some speakers have used words rarely heard in the rap world - words like "responsibility".

It remains to be seen whether fine words at the summit are heard where rap and hip hop are actually made - on the street.