Each time I see the musical "Show Boat," which opens aboard a floating theater on the Mississippi River in the late 1800s, I want to know more:

About Queenie, the cook who is ingenue Magnolia's warm surrogate mother. About Joe, the laborer whose profound rendition of "Ol' Man River" -- once performed by the legendary Paul Robeson -- pierces our hearts. About Julie, the musical's tragic, half-black heroine, played by Ava Gardner(!) in the 1951 movie.

In the current Kennedy Center production, Karen-Angela Bishop plays Julie, the fascinating mulatto whose interracial origins remain a mystery.

In real life, Bishop knows exactly where she came from. And, over lunch at a Harbor Place eatery in her native Baltimore, the vivacious actress produces a 29-page family biography -- compiled by her cousin Georgia for a reunion -- to prove it.

"They're all in there," Bishop explains.

"In there" are her ex-slave great-grandfather, David, mayor and co-founder of his North Carolina town's first "colored" school. And David's brother, Andrew, a riverboat gambler. And Bishop's great-grandmother Hannah, who, even after electricity and central heating were added to the family home, kept using a fireplace and kerosene lamps until she died at 90.

Perhaps it was Bishop's appreciation of her ancestors' vividness that sparked her fascination with lesser-known lives -- in the theater and everywhere else. Before playing Julie, Bishop spent a year in the "Show Boat" ensemble as one of more than 60 uncredited performers who she says are the show's "backbone" -- including the black servants and laborers who provide the play's moral context.

The actors came to represent Bishop's own unsung ancestors, the unknown forebears of all black Americans.

"Some people prefer to ignore the past; I choose to confront it and embrace it," Bishop says. "Despite the horrors that the people represented by that ensemble saw in that time period . . . they survived. And they came out of it with an incredible culture unlike any other in the world."

I learned of Bishop when I recently saw "Show Boat," Hal Prince's production of Jerome Kern's and Oscar Hammerstein II's groundbreaking musical about love, race and forgiveness. Curious about the talented mezzo-soprano playing the chanteuse who briefly passes for white, I searched Stagebill. Bishop's biography, far from the usual listing of past honors and credits, begins like this:

"A graduate of the Yale School of Drama (MFA 1993), Bishop is proud to be the great-great-granddaughter of American-born slaves." The bio, which details Bishop's ancestors' lives, never mentions that she attended Towson State University, appeared in regional theater across the nation and is recording a Christian contemporary CD with the group Plant The Seed.

What kind of actress, I wondered, ignores a prime opportunity to strut her accomplishments?

The same kind who asks, "Do you want to say grace first?" before tearing into a dish of crab dip at our lunch interview. Bishop, 30, is a willowy Manhattan resident who adores theater for its language, saying, "I love words' textures. I have favorites: Galapagos . . . lugubrious." She's thrilled by the play's proximity to Baltimore and her parents, Helen Marie and Elbert. An admirer of actors C.C.H. Pounder, who plays Dr. Hicks in "ER," and Gary Oldman, the Russian villain in "Air Force One," Bishop -- who once played Ophelia at Yale Repertory Theatre -- says classical theater is her first love.

As an African American who loves classic, American musical theater, I'm often frustrated by what isn't "in there" -- an in-depth examination of black life. "Show Boat," first staged in 1927, was perhaps the first major musical to suggest blacks even had feelings. Prince's production, closing here on July 19, opens with a scene highlighting separate water barrels for "colored" and whites. Still, the show's black characters remain so much background music to its white stars.

There's something sweetly ironic, and wonderfully American, about a character as narrow as Julie -- of whom all we know is her mixed heritage and blind devotion to the white husband who abandons her -- being played by a black woman so steeped in ancestral richness. Bishop accepts the role's limits with a shrug. "Not everybody can have a happy ending," she says.

"You can close your heart off to . . . understanding where everyone else has come from and become bitter," she explains. "But you lose so much. . . . Everyone has got a reason for doing what they do."

In art, what ends up "in there" is every artist's individual perspective. The white creators of American musical theater were creatures of their eras -- as I am of mine. So I'll keep loving their works for the heart-expanding music and themes they put in. And cringing at the thought of the myriad lives they left out.