When One Direction rolls into town Thursday, the collective sighs of Midwest tween and teen girls will pack enough oomph to inflate several Metrodomes. The British quintet of fluffy, sugar-dusted pastries with adorable haircuts are better known as Harry, Niall, Louis, Zayn and Liam to their fans, most of whom would just fall down and die — literally, die — if the objects of their extremely intense affection sidled up next to them and said "Hallo."

They wouldn't expect their mothers, or even anyone over 15, to understand why 1D (that's fan shorthand) are simply the best, the cutest, the sweetest, the most talented singing group ever born.

Sorry, girls, but this particular phenom's not new. Your mom, and maybe even your granny, went through her own version of the contained hysteria gripping your heart at the moment. It's been cycling around every several years since Beatlemania first hit the tarmac in 1964.

For proof, you need only check out New Kids on the Block, swinging through Saturday night on another reunion tour. They might be too long in the tooth and thin on the top for today's 12-year-olds to crush on, but about 25 years ago, they attracted as many high-decibel squeals and fevered mash notes as 1D does now (though in 1D's case, it's tweets and posts).

Whether they form organically or are manufactured in a pop-cultural petri dish, boy bands serve a very important purpose in the lives of girls of a certain age. Hint: It's not making music.

From the Monkees to Menudo, the Jackson 5 to the Jonas Brothers, the Bay City Rollers to the Backstreet Boys, boy bands are who you and your friends practice your fantasies on in order to prepare for real-life interaction. They're the transition between imaginary friends of your childhood and actual boys you know and might, like, go out with someday. And though musical styles may evolve, the essential ingredients to a successful boy band never change.

1. The more, the merrier. Justin Bieber has his beliebers, as did early-1970s dreamboat David Cassidy and other pretty-boy solo pop stars targeted at tweens and teens, but a whole group gives a pack of girlfriends more options, so they're not competing with their BFFs over the same star.

With 1D, Liam is "the smart one," Harry "the flirty one," Niall "the cute one." How it's determined that any one of these be-gelled cherubs is more attractive than the others is a matter of fiercely friendly debate. You like Harry, I'll take Niall. We don't have time for conflict because we have to tweet about them for the 29th time today.

2. Baby-faced is better. Soulfully blue-eyed Niall Horan and Harry Styles, whose neck seems ready to snap from the weight of his gorgeous brunet moptop, are the most popular members of One Direction. Same thing happened with Paul McCartney of the Beatles, Davy Jones of the Monkees, Donny Osmond of the Osmonds and Ricky Martin of Menudo. Why? They all have (or had) faces that are at most gender-neutral, some of them downright girlish, and they sing tenor, or even falsetto.

Boy bands are about as sexually suggestive as a teddy bear, and thus just as non-threatening, safely dreamy objects upon which to hurl unbridled — and unconsummated — affection. No 11-year-old wants to daydream about some bearded, cursing, pelvis-thrusting rocker — and her parents want that even less.

The members of 1D are all under 21, making them legit boys, but most boy-band idols are a bit older, so they have to look to Peter Pan for grooming tips to avoid alienating their target market with gross man stuff like too much hair anywhere but on top. That's why most are clean-shaven, and keep the number of scary tattoos to a minimum. For girls this age, nice beats nasty any day.

3. Singin' my life with his words. Fans will bristle at the mere suggestion that their crushes might not be the most musically original or talented pop stars to sell out an arena, but talent takes a back seat to personalities and lyrics. The successful boy band's songs must be easy for anyone with braces and a pink diary to personalize. One Direction's biggest hit to date, "What Makes You Beautiful," is brilliant for the way it taps into the psyche of adolescence with all its insecurities and vanities. Ditto for "Please Don't Go Girl," the 1988 NKOTB ballad, sung high and plaintively by then-bundle-of-squee Joey McIntyre (still pretty darn cute, at 40). There's nothing a young girl dipping a toe into the rejection-fraught world of romance finds more reassuring than being begged by a guy to stay forever and ever.

4. Gotta have a guru. Of marketing, that is. One Direction is the creation of TV talent-contest impresario Simon Cowell, who knows a thing or two about promotion. In the 1990s, Lou Pearlman was the mastermind behind both the Backstreet Boys and 'N Sync (in 2008, he was convicted of a far-reaching financial scam). As far back as 1966, the Monkees were pre-molded as America's answer to the Beatles — on a weekly TV show, no less.

Boy bands are packaged as a product to be gobbled like candy, by profiteers engaged in the pop-music equivalent of the smash-and-grab, cashing in before their stars' five o'clock shadow gets too dark.

While the formula still stands, one very significant modern twist affects both the perception and marketing of today's boy bands. In the old days, the only outlets were Tiger Beat, 16 and a couple of other fan mags from which to tear out a poster or six. Now YouTube and social media, plus a juggernaut of tie-in merchandise, have made nearly instant, worldwide adoration possible, with One Direction's more than 6 million Twitter followers as Exhibit A. The downside: Internet saturation can shorten shelf lives. Maybe that's why One Direction's 1D World pop-up store at Mall of America was shrewdly open for only six weeks last spring.

In the essay "Please Don't Go Girl" in Rookiemag.com last month, pop critic and former NKOTB fangirl Julianne Escobedo Shepherd summed up the essence of boy-band fandom:

"People who don't understand the process of crushing on someone you haven't met — and will never meet — might look at this as weird or antisocial, possibly even stalker-ish, behavior. But those of us who have been there know better: It can be a very useful way to figure out how you feel about dating, love and sex before you even want to consider it in real life. … Your fantasy relationship with Harry Styles is something you made up; you have all the control in this relationship. He's a mirage, a product of your own mind. You can make him whatever you want him to be."

Kristin Tillotson • 612-673-7046