(Washington Post photo illustration; Jason Merritt/Getty)

In pop music, the metamorphosis from horny boy-band caterpillar to oversexed butterfly solo artiste is a transformation as old as time — or at least as old as Justin Timberlake. After spending their most hormonal years pretending to be celibate Eagle Scouts, these hyper-famous lads tend to launch their solo careers by peeling straight off to the bedroom, eager to forge their adult identities in the greater erotic universe.

Zayn Malik's solo debut, "Mind of Mine," follows this boring trajectory to the letter. Having defected from the ranks of One Direction exactly one year ago, the 23-year-old has chosen to stretch himself out on a waterbed of anemic R&B, singing about his great sexual awakening while sounding as if he's half-asleep.

Garnished with dollops of show-offy profanity, the album's first single, "Pillowtalk" describes one particularly tangled tryst as "reckless behavior, a place that is so pure, so dirty and raw." On the surface, it's a mid-tempo bedroom ballad about the complicated nature of intimacy, but the song's underlying message is all but written in the sky: Zayn Malik is sexually active.

Here, and often throughout the tepid grind of "Mind of Mine," Malik's singing is both bombastic and lethargic, which always feels wrong. His lower register is satisfyingly robust, but his leaden phrasing has that ponderous, John Legend feel — and his falsetto never resonates at the aphrodisiac frequencies that Marvin Gaye taught humanity to expect of all desirous young men holding microphones.

It makes Malik's meandering lyrics an even tougher sell. Delivered with complete seriousness, his worst lines translate bad sexts into embarrassing poetry. During "Lucozade," a song named after a British energy drink, he punctuates a kiss-off with a crude question: "I told you I was over you — or were you under me?"

All of this joyless, pseudo-maturation raises a question: Does a pop song generate a hotter frisson when the singer isn't allowed to sing about sex? That might explain why so many teen-pop idols seem to exude so much life-force at the start of their careers. The wholesomeness that's being sold is a total lie and the kids are in on the secret. It also explains why grown-up-and-turned-on albums, like this one, feel like a deflation instead of a bloom.

On "Mind of Mine," Malik sounds most deflated during a song called "TIO," short for "take it off." It's a phrase that he repeats nearly 30 times over the course of three minutes, not once sounding like he actually wants what he's asking for, the murmuring of another promising heartthrob turned 20-something sex zombie.