"Hunter Gatherers," a dark comedy he describes as "Lord of the Flies" meets "Who's Afraid of Virginia Woolf?" is a departure from the shotgun laugh grab the Lobsters are known for, but it's becoming less and less of a departure for Nachtrieb. The boy who grew up "a drama nerd from way back" and was a lost boy in a Mountain Play production of "Peter Pan" is doing more writing than acting these days.

And writing more in the darker corners of comedy than might be expected of the boy raised in the drama departments of Marin's best private schools.

"Hunter Gatherers" is a play about a dinner party stripped of its dinner party decorum. At Nachtrieb's party, the hosts slaughter a lamb for dinner and the men wrestle for dominance. At Nachtrieb's dinner party, primal instincts are on the menu.

Nachtrieb would say that primal instincts and urges are on the menu in every facet of life. A man who majored in drama and biology likes to think of humans as "a product of evolution, as an organism."

We'd like to believe we left our inner caveman in the cave, but he's looking over our shoulder every minute, Nachtrieb contends. We are ruled, in large part, by our most primal urges.

"They color everything we do but we layer so much culture on top of it," Nachtrieb says. "There's definitely a big separation between how we live and our primal base."

It's certainly food for thought but in "Hunter Gatherers" it's also fodder for comedy. The Killing My Lobster actors don't get to toss out punch lines and mine their sketch concepts for cheap laughs. Director Tracy Ward wouldn't let them. But the laughs are there. They come from the ideas, she says.

Ward directs "Hunter Gatherers" and says Nachtrieb's characters aren't trying to be funny, they're being "true." It's just that "their truth is pretty outrageous," Ward says.

Nachtrieb's work is where realism meets the absurd, the director says. It's not an easy trick to pull off for anybody, for the actors, for the director, for the writer. But Nachtrieb's writing pulls it together, Ward says. "He's challenging in all the right ways."

The playwright has challenged himself when he could since the days when he was a "third-grade ruffian" in a elementary school play, through high school when he directed a full-length play at Marin Academy and on to Brown University where he spent semesters in the theater halls and summers watching fish spawn in Panama or counting lobsters in Maine on science projects.

He's been appearing in plays, finding commercial work and sending scripts into theater festivals. One of his plays got produced off-Broadway in a one-act festival that he says "opened a lot of doors." Like a lot of artists in the late '90s, he picked up some Web design skills and now finds contract gigs to pay bills between theater grants.

"I have time to not work," he says.

The biology background "colors all my writing and my world view." Taking that onto the stage would sound difficult, but Nachtrieb is inspired. "Hunter Gatherers" puts anthropology on the dinner table. A new project for the Magic Theater will explore nanotechnology in a dramatic setting.

His mom's not worried. If anybody can work nano into a script, it's her son. "He's always been an artistically daring," says Ursula Nachtrieb of San Anselmo.

His Marin Academy drama teacher has full confidence, too. Phoebe Moyer remembers her student as "an imaginative kid."

She wasn't surprised to find herself laughing at the concept of a dinner party complete with animal sacrifice and savage rituals.

"It's very dark and disturbing and at the same time very funny," Moyer says.

"That's Peter," his mom says.

"Hunter Gatherers" is playing in a loft-like space not so many blocks from the apartment Nachtrieb shares with the man he describes as "more than a boyfriend."

Another of his plays, "Colorado," will go up in a Berkeley theater housed in the basement of a pizza restaurant.

It's all very different from the Mill Valley where he grew up, but the Mill Valley he grew up in is a very different place, too, Nachtrieb says.

"You can trace the changes in Mill Valley by the changes at the Banana Republic," he jokes, recalling how the funky safari wear outfitter became a kind of upscale Gap. Things are more upscale all over his hometown.

Or at least they appear that way.

Nachtrieb knows that the basic primal drive "simmers below" the sophistication. You can put a caveman in a BMW but he's still a caveman. He may not slaughter lambs at dinner parties but he declares his dominance in the size of his plasma screen.

The hunter-gatherers just hunt and gather a little differently now.

And Peter Nachtrieb has a new hunting ground.

IF YOU GO

What: "Hunter Gatherers"

When: 8 p.m. Thursdays through Sundays through July 9

Where: Thick House Theater, 1695 18th St. in San Francisco.

Tickets: $20 to $25

Information: 558-7721 or www.huntergatherers.com