The popular history of reggae is simple: first there was Bob Marley, but he died. So now we have UB40 instead. Believe it?

THE STORY IS as long as you like. In one sense reggae has just come of age - it was 21 years ago that Toots & the Maytals released 'Do the Reggay'. But in truth it is as old as the ancient cultures of West Africa. The slaves, packed like sardines in the holds of British and Portugese ships, lost everything in the middle passage, yet managed to transport the culture of a continent to the Caribbean. Although African languages, religion and music were officially banned by their European masters, the slaves preserved them in secret. European saints were identified with African deities and plantation work was done to the rhythm of African religious drumming.

But that is all ancient history; switch the scene to 1950s Jamaica. The people want to dance. The dominant music is American R&B (Fats Domino, Louis Jordan) picked up, ionosphere permitting, from AM stations across the water in Miami. Somewhat louder are the "sound systems" set up for Saturday night dances: around 2000 watts of amplification delivering the beat to dancing feet in an outdoor venue. Curried goat is served along with crate after crate of bottled beer, while the DJ spins the latest imports high on his throne.

Rather suddenly, in the late '50s, the US got bored with R&B, and it became difficult to get hold of new music. Competition between sound systems was fierce, each vying for the freshest material. Almost in desperation, sound system bosses like Prince Buster, Duke Reid and Sir Coxsone Dodd began to get local musicians to record homegrown R&B instrumentals. For a time these bluebeat "specials" (recordings exclusive to one sound system) sufficed. But inexorably, a Jamaican style was allowed to emerge. So "ska" was born. The term refers to the off-beat rhythm guitar or horns in a 4/4 bar: 1-ska-3-ska, and so on. The shuffle of R&B, ie. a 6/8 feel in a 4/4 bar, is smoothed out in the JA version. This was the sound pioneered by Don Drummond and the Skatalites.

In 1966, straight ska was superceded by a new dance sound, "rocksteady". As the name suggests, this was a slower, rock steady 4/4 rhythm, the emphasis still on the second and fourth beats of the bar. Legend has it that the hot summer of this year sapped the strength of the frenzied ska crowd, who demanded something cooler to dance to. Whatever the reason, the difference is there: tempo apart, the bass takes centre stage for the first time, playing central, repeated riffs often in unison with a plucked guitar, backed up by drums simplified from the jazz-ride style of ska. The off-beat horns give way to a rhythm guitar, confining themselves to melodic fills. The style quickly became associated with the Rude Boy phenomenon, forerunner of the skinhead style, complete with ten-inch blades, handguns and the ubiquitous CB200 motorbike.

A certain Lee Perry claims to have invented reggae. Fed up with the predictable sound of ska and rocksteady, he plotted a more menacing, rebel rhythm, slower still than rocksteady, and even heavier on the bass. "Reggay" began with a 1968 Perry-produced track called 'People Funny Boy'. But in truth, the chasm between rocksteady and reggae wasn't all that big initially. It would be ludicrous to try to classify every record of the period as one or the other. What we can say is that a new feeling came to the music.

Rasta consciousness was now part of the music. "Locksmen" had been around in Jamaica since Marcus Garvey's teachings of black nationalism and repatriation, and his prophecy of a black Messiah, early in this century. When Haile Selassie (aka Ras Tafari) was made emperor of Ethiopia, the locksmen hailed him as the Messiah. The spirituality of Rasta had been an influence on musicians for a long time, as had the distinctive Rasta drumming, derived from the "Burru" rhythms of West Africa. The late '60s and early 70s, however, saw many established groups and musicians taking Rastafari to their hearts and heads.

The earliest successful Rasta-orientated record was 'Blood and Fire' by Niney the Observer. Dashed off in a hectic hour (it was all he could afford in studio time), it became a hit in Jamaica. But it was Bob Marley & the Wailers who were to bring the new Reggae music and its Rasta influences to the notice of the whole record-buying world. Marley's story is well recorded: his apprenticeship as a struggling solo singer, the coming together of the Wailers, their "discovery" by plantation owner's son Chris Blackwell (founder of Island records), the relentless marketing of the first albums, reggae being packaged for the rock audience... and the ensuing "outernational" success.

Curiously, the success of Bob Marley & the Wailers had the effect of obscuring almost every other Jamaican artist. On the island, reggae continued to develop and diversify, and diversification inevitably meant a split. If you sang songs, you went one way; if you chatted lyrics, you went another.

The singers also fell into two categories. First there was the reggae group which, like the Wailers, was influenced by Rasta culture (hence the name "roots" music), and for whom live performance was as important as recording. Of the Jamaican groups, Burning Spear, Toots & the Maytals and the Mighty Diamonds created the strongest reputations. World class reggae groups emerged from the UK too, in the shape of Steel Pulse, Aswad and Misty in Roots, and the little-known but outstanding Cimarons.

Alongside the groups there emerged a culture of solo singers, centred around studios. Two studios in particular deserve attention for their impact in the late '60s and early 70s. Duke Reid's Treasure Isle and Coxsone Dodd's Studio One used house bands to create unique sounds. In this environment, stars like Alton Ellis, Denis Brown, Bob Andy, Marcia Griffiths, John Holt and Delroy Wilson sang of love, freedom, bitterness and pride to the most beautifully crafted backing reggae can boast. These classics are treasured today in the same way as early 70s "rare groove" soul, and it's often the rarest tracks by the least-known artists which fetch the highest bids. The "Lovers' Rock" of later years, featuring many of the same artists, is the direct descendant (or bastard child, depending on your point of view) of that enchanted period.

Meanwhile, a radical new style was beginning to evolve: the art of the talkover. Back in the '60s, sound system operators used to shout favourite phrases of encouragement to the sweating dancers, giving the dance instrumentals that little extra spice. A DJ for King Tubby's system who called himself U Roy started to perform monologues over the records he played. He would shout, scream, woop, chatter - anything that sounded good. His unique style became popular, so much so that around 1970 he actually started chatting on record. He had a host of followers and imitators, among them I Roy, Big Youth, Tapper Zukie and Prince Far-I. This was no transient craze, but the start of the most enduring reggae style: that of the "MC" (originally "Master of Ceremonies", but now glossed as "Mike Chanter").

The second, and present, phase of MC development began in 1985 with the introduction of wholly synthesized rhythms. Jamaica again took the initiative as the cult of the "ragamuffin" spread. Ragamuffin is variously explained either as the '80s rude boy craze or as the new collective confidence of black urban youth. Whichever, it was as if the latest studio technology released a new creative energy in the musicians who built the rhythms, and a new self-confident expression in the young people who bought the records (or taped them from pirate stations) and improvised their own versions over the rhythm. And youth really means youth in this case: Little Kirk was only 15 when he voiced his brilliant hits, 'Screechy Cross the Border' and 'Ghetto People Broke'.

Roots bores who wanted to strangle ragamuffin at birth were mistaken in their assessment of the music as shallow - as much as the ragamuffin MC deals with the local, the domestic and the everyday, he or she speaks with the inspiration of the Rasta spirit. If you've missed out on the hi-tech reggae explosion, catch up before it catches up with you.

Like the digital samplers of today, DJs and MCs have been less than popular with the musicians' union in Jamaica. When an MC talks over the instrumental "version" of a song, the musicians receive no extra royalties. Yet in fact "versioning" is an element in the creative process of reggae. If the rhythmic pattern, bassline or even tune of a record is well liked, it's copied and recycled as a matter of course. It's less a question of theft than of admiration - a different attitude to intellectual property.

MCs have continued in an unbroken line from U Roy. But the tradition has been far from uncomplicated. Just like sound systems, MCs thrive on competition and rivalry. And, as in rap music, the rivalry and boasting inevitably takes over. The logical extension of this was the style of "slackness" typified by Yellowman. Characterized by self-satisfied monologues on the themes of women and money, slackness was seen as the moral bankruptcy brought on by the death of Bob Marley, and by the American influence courted by Jamaican Prime Minister Edward Seaga in the years following his victory in the violent election of 1980.

Since that low point, the development of the DJ/MC in this decade has been exciting and fast-moving. The first phase came with Yellowman's contemporaries: Barrington Levy, Charlie Chaplin, Little Billy Boyo, and Josey Wales. Their output was phenomenally high and erratically brilliant.

For a brief period, in 1984-5, it seemed as if the crown had passed to British MCs, particularly the excellent Saxon posse. Putting their own mark on MC history with the "fast-style" delivery, Tippa Irie, Asher Senator, Phillip (Papa) Levi and friends presented a smart, witty image of the streetwise young black Briton. Smiley Culture's 'Cockney Translation' and 'Police Officer' became national chart hits, while Papa Levi produced the ultimate cultural odyssey in the classic 'Mi God Mi King'.