When Take That - the five-piece pop group first thrown together in 1989 to cash in on the popularity of late-1980s über-stars New Kids on the Block - announced they would be touring in 2011 for the first time with their original line-up in 15 years, sales went ballistic. Ticket lines crashed due to demand, the UK telephone network itself was threatened, and more than a million seats were sold in a single day.
Not bad for a bunch of dudes approaching middle age, whose first single reached a paltry number 82 on the British charts - any group that underperformed that badly today would be back working at the supermarket till sharpish.
So what is it about the formula of a handful of over-styled guys, vocal harmonies and clean-cut grins that still makes pop fans weak at the knees? And is nothing different since Robbie, Gary, Howard, Jason and Mark made their first music video back in 1991?
For a start, the market wasn't as crowded with pop acts back then, meaning that groups could take their sweet time crawling up the charts and establishing themselves - it took Take That eight tries before their first number one. New Kids didn't even chart with their first couple of songs, when they were put together by their manager Maurice Starr as a white version of his Jackson 5-ish singing-and-dancing group New Edition. But when they hit the big time in 1988 with Hanging Tough, other producers tried to get in on the act. And so, the golden age of the boy band was born, when you could get away with crooning to an audience of pre-teen girls, while wearing baggy jeans, chunky knit sweaters, floppy hair in a centre parting, or all three.
The 1990s saw a parade of unthreatening boy bands with choreographed moves, music that borrowed from R&B, and a selection of personality types within each band that ensured every 14-year-old girl could find a favourite to match her type, whether it be "the sensitive one", "the joker", or "the bad boy". The US had the Backstreet Boys, 'N Sync and Boyz II Men; the UK boasted East 17, Boyzone and Westlife. Millions of records were sold, huge tours were mounted, and hummable tunes were etched deep into the psyches of women now in their 30s and 40s, who - if ticket sales are anything to go by - are still overwhelmed by a hormonal rush when they hear that the heroes of their teenage years are back together and back on tour.
The noughties saw a few new extensions of the basic boy-band template: Busted and McFly borrowed from guitar pop and claimed to write or co-write their own material while sticking to the genre's basic conventions. Meanwhile, the arrival of televised singing competition The X Factor, which launched in Britain and has been franchised and copied around the world (pan Arab versions include XSeer Al Najah, and the Lebanese programme Star Academy, based on the Endemol show of the same name that was first broadcast in France), has ushered in a new era for boy bands. Not only has it created one of the UK's biggest current boy bands, JLS, and provided promo spots for the likes of Westlife and Take That, it also changed the way vocal groups are marketed.
Why spend years building a fan base at the bottom end of the charts, as Take That did, when you can cull your group's members directly from TV, ensuring an audience that has already fallen for them? The suits behind America's newest generation of singing heartthrobs, the Jonas Brothers, made good use of this principle, finding their protégés a prime-time spot on the Disney Channel's Hannah Montana, a performance in the Disney Channel Games, and starring roles in Disney movies Camp Rock and Camp Rock 2; they've now got their own TV series. Combined with their family-friendly, good-guy image, it's a winning formula: they've got three platinum albums and 14 Teen Choice awards to their name.
With cute, clean-cut brothers, hip-hop-flavoured boy bands such as JLS, and a new crop of emo rock acts for fans of male vocal groups to choose from, why are people still buying millions of tickets to see ageing groups such as Take That, or Backstreet Boys, who have been touring successfully every couple of years since their 1990s heyday? The answer is nostalgia: "man bands" don't need to worry about hooking young fans when their original ones are so loyal. It's just been confirmed that New Kids on the Block and Backstreet Boys will be touring together next year: let's hope America's telephone grid can withstand the stampede for tickets.