Most of us grew up with Mr. Rogers telling us we were special. Implicit in that declaration is that the locus of self-worth, of our ability to deserve love -- both from ourselves and others -- lies in our uniqueness.

So what happens, posits Caryl Churchill in "A Number," when there are two of the same person (or 20 or 100) running around?

"A Number" is, on one level, about cloning, and it has its "Twilight Zone" aspects. The very astute production at Pittsburgh Public Theater, under the direction of Jesse Berger, plumbs the many layers of Churchill's brief drama. In its 60 minutes, "A Number" manages to ask deep moral questions, not just about the interplay of science and ethics, but also about personal culpability, about the factors that shape personality and about what, if anything, constitutes the essence of a human being.

As if that weren't enough, Churchill also offers her own version of domestic drama, a classic father-son struggle re-imagined. Typical of Churchill's work, form follows function. Short scenes, simply arranged, highlight dark parallels, and the language -- fast, cryptic and disjointed -- speaks at once to an inability or unwillingness to communicate fully and to our text-messaging life of shorthand dialogue. IOW, Churchill doesn't dismiss progress of any kind by bemoaning its negative impact. She allows it to play out and delightfully displays the questions it poses.

Salter, the father, only gradually reveals the events that led to the cloning of his one son. In the hands of Sam Tsoutsouvas, Salter is an extraordinary character, part blustering Zeus, part wasted scoundrel. Tsoutsouvas brilliantly captures the element of personal tragedy in "A Number," that bewildering, complex dance that fathers and sons perform. He also nails Churchill's humor, which finds its roots certainly in a general absurdity (there is more than a whiff of Beckett here) but also in the darkly comic potential of science taken to the extreme.

Craig Baldwin plays three of the clones. One after the other shows up to confront Salter. It's to Baldwin's credit his three characters are so distinct, bringing to the forefront Churchill's nature vs. nurture puzzle. In the stoop of a shoulder, a clenched fist, a furrowed brow, thinned lips, Baldwin is another person, no one less real than the other -- an important accomplishment when what is real is at the heart of the play. "I'm just a copy. I'm not the real one," complains one of the clones.

Berger and scenic/costume designer Beowulf Boritt play artfully with this dilemma. Can the difference between the clones be as superficial as an actor changing costumes? Berger forces the issue by having Baldwin change costume pieces on stage. Articles of clothing are pulled from one of the many boxes that form the towering set. Each box is labeled with a set of numbers, so it's as if the personality, the person, is pulled ready-made from these boxes of scientific data.

Boritt adds another dimension to "A Number" with a set that, when darkened, looks ominously like a city skyline. Lighting designer Scott Zielinski illuminates several boxes, and suddenly they're windows in rows of nondescript apartments. Do we need to reach the point of human cloning to experience the crisis of identity that Churchill depicts or has life and the world we've built already brought us there?

Perhaps, emphasizing personal difference is misguided in the first place. Could Mr. Rogers have been wrong after all? "A Number" will leave you with much to ponder long after you leave the theater.