The handful of viewers who watched the BBC's earliest public television broadcasts in 1936 would have seen little of the diversity we now expect from the medium. The short transmissions, following patterns established by radio and the music hall, offered a variety of light music, dance, comedy turns and conversation - almost all of it transmitted live, as it continued to be well into the 1950s. The genres and formats we know today emerged later.

The arrival of ITV in 1955 ended the BBC monopoly, and many new formats are the result of the rivalry between the two broadcasters. Light Entertainment became a big draw, with Rediffusion's Sunday Night at the London Palladium winning huge audiences away from the complacent BBC. The newly-formed ITN reinvigorated news broadcasting, while This Week was Britain's first modern-style current affairs programme, introducing a previously unknown critical edge to political reporting.

In 1956, the BBC transplanted Tony Hancock's successful radio show Hancock's Half Hour to television and in the process created Britain's first recognisably home-grown situation comedy. Over the next few years, the sitcom became the form by which the BBC reasserted its strength, with shows like Steptoe and Son (1963-65; 1970-74) and Till Death Us Do Part (1966-75) winning huge audiences. The 1960s also saw a new 'satire boom', heralded by the success of TW3 (BBC, 1962-63). Comedians like Spike Milligan and the Monty Python team took the sketch show into new territory.

Although the earliest TV soap operas - like The Grove Family (1954-57) - appeared on BBC, it was Granada's Coronation Street (1960-) which defined British soap. The show led its field, shrugging off challenges by the likes of ITV rival Crossroads, until the mid-1980s, when Channel 4's Brookside (1982-2003) and the BBC's EastEnders (1985-) reintroduced the 'gritty realism' that had been a feature of Coronation Street's early days, but which the show had since abandoned for acute social comedy.

In drama series, TV's fondness for police and medical settings dates back to at least the 1950s, although there is a world of difference between Z Cars (BBC, 1962-78) and The Bill (ITV, 1984-), or between Dr Finlay's Casebook (BBC, 1962-71) and Casualty (BBC, 1986-). Meanwhile, the appetite for adaptations of classic literary works has ebbed and flowed, although there is less demand for swashbuckling adventures than there once was.The single drama reached a peak in the 1960s and 70s, before declining in the 1980s, although it has never quite gone away.

In documentary, the period since the 1960s has seen the rise of the 'authored' documentary, as exemplified by Civilisation (BBC, 1969) and The Ascent of Man (1973), as well as the 'fly on the wall' genre. Meanwhile, filmmakers like Nick Broomfield began to examine the myths of documentary objectivity, exposing the process of filmmaking to public scrutiny.

The form and style of presentation in news, sport, documentary, music and children's programmes have changed a great deal over the decades, just as they have in drama and comedy. Some forms, like breakfast television or 'confessional' TV, are relatively new, while others date back to the medium's earliest days.

If one thing is certain in today's multichannel age, it's that television formats will continue to adapt, mutate and multiply, in an accelerated version of the evolutionary process that one TV genre - the natural history documentary - is so good at explaining to us.