Generally, the life cycle of a boy band can be measured with scientific precision. A couple hit albums; stadium tours; crazed fans; album quality drops; one guy goes solo; tween fans grow up; you’re done.

So in scientific terms, One Direction might be a modern miracle.

Instead of fading away, as most boy bands tend to do after several years, the group appears to be stronger than ever. The guys just released their fourth album — the uncreatively-titled “Four” — this week. As critics noted, the fact that the band simply got to album No. 4 makes them an anomaly.

Just look at the numbers: So far, each album the group released has outperformed the one before it in the debut week. The third, last year’s “Midnight Memories,” may have settled for less total sales than the previous two, but it still sold 564,000 copies its first week: It was a record-setting accomplishment, making One Direction the first group in history to debut with three No. 1 albums in a row.

Billboard assistant editor Jason Lipshutz said it’s tempting (but still difficult in a fickle music industry) to forecast how long One Direction’s unusual dominance is going last. Still, it’s undeniable that the band has had an incredible run so far — and One Direction is squeezing in an unusual amount of hit music, Lipshutz said. Typically, the third album begins the decline, as with groups including NSYNC and Backstreet Boys. While they still had hits, they weren’t nearly as big as when album No. 2 came out.

“One Direction proved to be the exception to the rule,” Lipshutz said. “They still put out a ton of successful music — part of that is releasing so much in such a little time frame.”

In fact, “Four” is the fourth album in just as many years, following up “Up All Night” (2011), “Take Me Home” (2012) and “Midnight Memories” (2013). The flurry of releases is strategic, as you never know when, say, Harry Styles will want to go solo. After all, the typical boy band apex of popularity clocks in at about five years or less (NSYNC, for example, was 1997 to 2001.) So it’s best to pump out as much music as humanly possible in the golden window when they’re still hot.

Lipshutz calls that “super-serving fans.” In other words, “Making sure they have a new album to buy, new songs to hear on the radio, new songs to sing along to on stadium tours,” he said, adding that the sheer volume of One Direction material available “is pretty remarkable.”

One Direction also has the advantage of being a boy band in the digital age, when #FOUROutNow can trend worldwide for hours to remind fans to pick up that album; and things like hashtag voting for the guys on MTV’s Europe Music Awards keeps millions of “Directioners” engaged. Although the core tween fanbase can obviously grow up and lose interest, these days, there’s just so much more exposure — between Twitter, Instagram, Vine, YouTube — that fans can never really lose sight of the band. Most importantly, it gives them a personal connection that keeps them invested.

Right now, music experts are keeping a close eye on the charts for “Four.” It’s definitely a departure for the guys, heading into even more of a classic rock sound than their very poppy debut, which scored big with songs like the cheerful “What Makes You Beautiful.” This could be a gamble — the first single off of “Four,” called “Steal My Girl,” debuted at No. 13 on the Billboard charts, a dip from previous songs.

Then again, One Direction scored the second-biggest single hit of its career, “Story of My Life,” on its third album, proving fans liked a new sound. The group already announced a stadium tour for 2015. All signs point to that, just like the new album, being a success.

Overall, Lipshutz​ said, “It’s hard to say when this thing is going to end.”