Opposites attract (viewers, that is)

Who knew that Ashton Kutcher would become a social and ethical barometer of our time?

Since he debuted “Punk’d” on MTV in 2003, it’s been clear that he’s unusually keyed-in to the frailties of celebrity culture. The hidden-camera prank show, which set up celebrities in ridiculous situations, was less about embarrassing the famous than about exposing what they were like beneath the veneer of stardom, for better or worse. It coincided neatly with the rise of tabloid magazines that juxtapose two sides of celebrities -- how they desire to be represented and how they actually behave -- and presaged the rise of online video tabloids such as TMZ.com, which capture stars and pseudo-stars ruthlessly and unforgivingly.

But there is no better punk than reality. Just as “Punk’d” thrived on unpredictability and playing against type, Kutcher’s second entry into pseudo-reality television (along with producing partner Jason Goldberg) also hinges upon defying expectations. Beginning its third season on Wednesday, “Beauty and the Geek” (the CW, 8 p.m.) is one of the most endearing and engaging reality programs, largely because of its core belief that people, even walking stereotypes, contain a capacity to transform.

“Beauty and the Geek,” in which pairs of B&Gs; compete, also stands apart in its self-conception as a “social experiment” as opposed to a long-form game show, even though the winning team of beauty and geek take home $250,000. It’s highlighted at this season’s first elimination; rather than the show’s traditional face-off between two teams nominated to go home, in the first episode teams are tempted with money -- are they in it for the cash, or for the experience?

Ultimately, no one takes the bait, and what a relief. “Beauty and the Geek” is the only reality show in which greed is punished, and which tests the earnestness of people’s intentions. And watching the geeks introduce themselves, it’s hard not to believe in just how seriously they’re taking their participation in the show. They’re not so nerdy that they’ve never seen, or wanted to participate in, reality television. But still -- they’re pretty nerdy. Speaking about women, “Star Trek” devotee Drew laments, “It’s as if they’re Romulans and I’m the Federation.” Gripes tech-loving Sanjay, “One thing that makes me mad about women is when they don’t know about Linux.” He later tries to impress the ladies with an impression ... of a blender. (There is a host, Mike Richards, but he’s inoffensively bland, probably so as not to create an obvious testosterone centerpiece.)

If “Beauty and the Geek” fails at all in its mission, it’s due to a slight misogynistic streak. No matter how poorly they perform in challenges, the nerdy men can’t get much more unappealing. Clearly, though, some schadenfreude is at play watching attractive women get taken down a notch as they struggle with their assigned tasks -- in the first two episodes this season, that includes fumbling with the Dewey Decimal System and, in a wonder of product placement, a TV news interview with a barely-holding-it-together Stephen J. Dubner, co-author of “Freakonomics.” Both sides are here for growth, but only one is really ripe for humiliation. (Perhaps a gender switch is in order for next season?)

Every herd has it codes -- it’s how assiduously one sticks to them, or one’s willingness to break rank, that makes one cool. “Beauty and the Geek,” of course, rewards such change. Much like the Woody Allen-ish virgin Richard Rubin of Season 1, this season’s obvious breakout star is Nate, who sports bushy hair, proudly wears contrasting plaids and red Crocs and fronts a “Star Wars” tribute band. In a videotaped introduction, Nate sings a verse from one of his band’s songs. Similarly, in her introduction, Nadia, one of the beauties, gleefully recites the cheers she perfected in high school and clearly never let go of. The show’s just getting started and, by comparison, Nate already seems kinda cool. How about that.