win-pop is shaping up to be at least as important a trend and sociological reality in 2006 as tween-confessional, bubblecountry, MySpace, or High School Musical. The term (as I’m using it) encompasses music made by identical twins, fraternal twins, brothers, sisters, and sometimes people with no biological relation at all, provided the overall effect is of one performer and his or her conceptual double. It includes all subgenres of teenpop and is performed by major label artists like the Veronicas as well as MySpacers like Brit and Alex and Sammy & Sasha. Occasionally, it includes triplets. Twin fever was big in Russia, and has since swept through Poland, Israel, and, most recently, Poland again.

The origins of the current wave of twin-pop, sib-pop, and pseudo-twin-pop at least dates back to the mid-90s, when the sitcom Full House completed its eight-season run. The Olsen twins, both of whom starred as Michelle Tanner, were cast in the role simply as a way to circumvent child labor laws. But as the series developed, audiences, fully aware of Michelle’s true dual identity, grew to love the idea of the twins and wanted to see both onscreen at once. It happened twice: in the episode “Greek Week,” Mary-Kate Olsen doubled (tripled?) as the Tanner family’s cousin Melina, and in the series finale the twins appeared together to resolve the episode’s conflict (Michelle gets amnesia after a tumble off of a horse, and one twin restores the other’s memory). In one of their final gestures as “Michelle,” both twins fuse together into one body.

So why do we love twins? On TV it could be seen as a fascination with production coupled with devotion to the star, the same combination that transformed the Olsen twins into an industry. Twin-pop functions in a similar way; twin performers let listeners “inside” the music’s production (listeners hear harmonies in real time, or at least think they do) while positioning themselves as pop stars.

The relationship seems paradoxical—audiences embrace production and performance-oriented “authenticity” standards (of which non-twin Ashlee Simpson was a victim during her SNL and Orange Bowl appearances and has since rebounded—unfortunately, she’s barely getting 50% attendance to her now indisputably “authentic” and kickass live shows…just the sort of final ego blow that might compel her to surgically remedy the few differences between herself and her sister to become Jessica’s twin!) while simultaneously appreciating pop music that is, by those same dubious standards, often marginalized as “inauthentic” by anyone outside the influence of the teenpop star system.

But this explanation doesn’t get to the heart of twin-pop’s unique attraction. In 1999, Marit Larsen and Marion Raven forged a framework for twin-pop that defines “twins” as something more like secret sharers. They witness, and perhaps contribute to, each other’s struggle to define their own identities, but, in struggling together, stuck side by side in isolation, they assume a single multivalent persona: M2M.

“Give a Little Love,” from M2M’s debut Shades of Purple, subtly exposes two distinct personalities from within the pronoun “I.” Both singers have very different reactions to a boyfriend’s mistreatment: Marit Larsen, cautious and patient, understands that she still loves him (“every time I think I’ve had enough of you I take you back again”) even though he acts differently in front of others than he does with her. (A premise that Avril Lavigne would lift wholesale in “Complicated.”)

Marion Raven, here the Hyde to Marit’s Jekyll, commands, “Get down on your knees!” Like Avril, she answers her boyfriend’s own crisis of identity with a blunt kiss-off, contrary to the redemptive chorus (both M’s on vocals) emphasizing love and understanding. So who is referred to in the line “have a little faith in the two of us”? Does M2M seek reconciliation with its boyfriend or with its own apparent division? Should he love M2M or two women?

M2M acknowledges the fragmented self that twin-pop reveals unconsciously. This is one reason why twins maintain a unique position in the currently ebbing tide of confessional teenpop, where automatic identification with an emotionally conflicted figure is crucial. Confronted by a literally fragmented persona—their own secret sharer—conflicted listeners (we? OK, “I”) connect to implicit disconnect.

But this disconnect isn’t limited to a specific style of music or representation. M2M uses the dual “I” to create tension in narratives where a straightforward lyrical reading without context would be incomplete; the Veronicas approach the disconnect self-consciously; Aly and AJ (not twins but close enough) have approached it alternately with confidence (we’re all in this together) and dread (we’re all doomed); even neo-Nazi twin-poppers Prussian Blue approach it in solidarity. The disconnect makes these duos funnier, stronger, scarier. In the case of sister-pop duo Smoosh, possibly indier.

In each of these examples, the attempt to fuse two personalities into the “I,” or to achieve the “Michelle moment,” immediately provides an external layer of meaning often unavailable to solo performers. Kelly Clarkson, among others, manages to convey a fractured identity effectively without the aid of a doppelganger—but not all acts can hope for her songwriting abilities, populist everywoman appeal, or impeccable production.

That might be one reason why Disney has substituted fairly obvious dual identity fusion for character depth in its two most successful projects of the year, High School Musical and Hannah Montana. In HSM, the one-dimensional drama queen antagonist is divided into Sharpay and Ryan Evans (Ashley Tisdale and Lucas Grabeel), presumably fraternal twins, in part to underscore the film’s playful subtext of sexual ambiguity (nearly all of the film’s characters are bi-curious in their gendered extra-curricular activities). Miley Cyrus’ alter ego provides an outlet for one subgenre of teenpop (bubblegum pop country), while her “real” character is allowed a more earnest form of expression—Miley, not Hannah, performed the show’s only ballad to date. Hannah, meanwhile, references her “other side” in almost every song.

But there’s still something immediately satisfying about seeing identity conflict fought out or toyed with between two or more performers before your eyes. One Ashlee Simpson can sing about the “Pieces of Me,” but a thousand Ashlees might actually show them to you—a more impressive feat while they’re all trying to navigate those unruly harmonies.