On March 8, 1998, the Fox television network aired an episode of its long-running animated hit “The Simpsons” titled “Lisa the Simpson.” It was neither the first nor the most famous episode devoted to the show’s fiercely intelligent, spiky-haired eight-year-old middle child but, for pop-culture addicts who love outspoken female characters and recall the particular obsessions and anxieties that come with being a girl of grammar-school age, it was certainly one of the most provocative.

“Lisa the Simpson” probes the potent, heady threshold between childhood and early adolescence, when many girls experience crippling doubts about their self-worth—what the psychologist Carol Gilligan has called “going underground.” In the episode, Lisa experiences a crisis of confidence when she can’t solve a brain teaser, deciding that something terrible has happened to her mind, and that she is doomed to a stifling life of motherhood and daytime-soap-opera watching. “It can’t just be a bad day. I think I’m getting dumber by the minute,” she confesses to her mother, Marge. After a run-in with a female jazz musician who emphasizes the importance of sharing one’s truths with the rest of the world, Lisa decides to deliver a desperate tribute to what she believes to be her quickly deteriorating mental abilities. She scams her way onto a local news program, where she implores viewers to nurture their brains with two wonderful books: “Harriet the Spy” and “To Kill a Mockingbird.”

Lisa Simpson was onto something when she invoked these two novels as an antidote to forgetting, and to forgetting yourself: her character is, after all, a spiritual descendent of both Jean Louise (Scout) Finch, the plucky six-year-old protagonist of Harper Lee’s Pulitzer Prize-winning 1960 novel, and Harriet M. Welsch, the nosy, opinionated, and obstinate eleven-year-old heroine of Louise Fitzhugh’s 1964 children’s classic, which celebrates its fiftieth anniversary this spring. And, in the same way that Lisa has been celebrated as a feminist hero since her creation, by the cartoonist Matt Groening, in 1987, millions of women and girls, myself included, have long considered Scout Finch and Harriet M. Welsch two of the most important American examples of enlightened, audacious girlhood. In fact, I’ve long suspected that “Harriet the Spy” was heavily influenced by “Mockingbird.”

The story of a six-year-old girl observing the oppressive racial politics of the fictional Maycomb, Alabama, in the nineteen-thirties may not seem to much resemble that of a sophisticated, eleven-year-old Upper East Sider taking notes on the petty social mores of her peers in the nineteen-sixties. But the books share thematic concerns—concepts of truth, justice, and self-actualization—as well as a number of details. Both are centered on grade-school tomboys who love denim and sensible shoes. Like Scout, Harriet has an absent—in her case, uninvolved—mother; comes from an economically privileged family; and is contemptuous of frailty and friendly with filth. Both are rough-and-tumble, foulmouthed, mostly male-identified girls who are fascinated by the people in their neighborhood, and both butt up against expectations of their gender—“I’ll be damned if I go to dancing school!” Harriet bellows at one point. And each book argues for authentic expression in favor of fealty to convention.

There is no evidence that Fitzhugh, who died of a brain aneurysm in 1974, at the age of forty-six, ever met Nelle Harper Lee, who is now eighty-seven years old and living in Monroeville, Alabama. Nor is there evidence that Fitzhugh had an opinion about “To Kill a Mockingbird” (Lee’s only book), although she must have been aware of its immediate and huge success; it was published the year before she began work on “Harriet the Spy.” But, half a century after the publication of “Harriet,” I’m convinced that there is a close connection between these two books and their ideas about the complexity, sophistication, and occasional wickedness of young girls’ imaginations.

It is perhaps unsurprising that these two writers yielded up such similarly contrarian female characters: there are marked likenesses in their biographies, and they seem to have been shaped by similar forces. Louise Fitzhugh was born in 1928 in Memphis, Tennessee. Like Harper Lee, who was born a few hundred miles to the south, in Monroeville, Alabama, two years earlier, Fitzhugh was the daughter of a successful, widely respected attorney and an unavailable mother. (Lee’s mother died when she was twelve; Fitzhugh was raised by her father and his second wife and rarely saw her mom, a dancer and performer who reportedly suffered from mental illness.) Like Lee, Fitzhugh was an outsider—Virginia L. Wolf, the author of the only book-length critical study of the author, describes the utter loneliness that Fitzhugh felt as a child—but she was nonetheless energetic and opinionated, a tomboy in a social and cultural milieu that insisted on demure obedience from women. Like Lee, Fitzhugh eventually migrated north, to New York City, where she met many other writers and artists. (Unlike Lee, who shuttled between Alabama and New York, Fitzhugh stayed.)

Lee never married, and after the publication of “Mockingbird” the reclusive writer returned to her home town, where she moved in with her older sister. Fitzhugh married once, very briefly; she defied her parents’ wish that she become a debutante, and instead eloped to Mississippi with a high-school classmate, a marriage that, according to Wolf, may have been a way of quelling rumors about “a scandal about Louise and another female student.” (The union was quickly annulled.) In 1960, more women than ever were marrying, and at younger ages; it’s possible that Fitzhugh and Lee, whose protagonists are considered by biographers and scholars to be their alter egos, were registering their protest against the ubiquity of marriage and subtly agitating for female independence. (Betty Friedan’s “The Feminine Mystique” was published three years after “Mockingbird.”)

Both Fitzhugh and Lee’s heroines are uninterested in, and occasionally contemptuous of, heterosexual coupling. (You can’t blame them: there are few, if any, functional romantic relationships in either book.) At one point, Harriet jokingly announces that her best friend, the brooding, timid Sport Rocque, is “my husband”; later in the book, while listening to her parents relate the story of their own courtship, a vision of Sport comes to mind, and she imagines committing an act of physical violence against him. Though Scout’s closest male companion is her older brother, Jem, she and her best friend, the towheaded Charles Baker (Dill) Harris, briefly conduct half-hearted, playful attempts to get engaged. “Dill had asked me earlier in the summer to marry him, then he promptly forgot about it,” Scout explains. “He staked me out, marked as his property, said I was the only girl he would ever love, then he neglected me. I beat him up twice but it did no good, he only grew closer to Jem.”

If, in “Harriet the Spy” and “To Kill a Mockingbird,” grade-school boys are to be embraced, even emulated—though maybe not married—girls and their adult female counterparts are to be disdained or, at the very least, merely tolerated. Both Fitzhugh and Lee are clear from the get-go that their heroines have few, if any, female friends or role models. (Both girls have complicated, though loving, relationships with their families’ domestic servants.) They prefer pants to dresses and the freedom of the outdoors to the rigid confines of home. Harriet makes no secret of her revulsion for the preciousness and learned helplessness of the female peers and adults she encounters, scorning prissy, goody-two-shoes classmates like Marion Hawthorne and Rachel Hennessey and directing some of her most malicious observations toward her neighbor Agatha K. Plumber, a wealthy divorcée with a flair for drama, who spends her days in bed, talking on the phone, eating candy, and ordering her maid around. (“SHE IS A VERY STUPID LADY,” Harriet writes.) Scout, who sometimes feels suffocated by what she calls “the starched walls of a pink cotton penitentiary,” also bristles against what she sees as female fragility. She resents the influence of her genteel aunt Alexandra, who loathes dirt and wishes that her niece would play with stoves and tea sets; is disgusted by her hateful, elderly, and bedridden neighbor, Mrs. Henry Lafayette Dubose; and ridicules her first-grade teacher, Miss Caroline Fisher, a “peppermint drop” of a pretty, proper young woman.

Harriet and Scout define themselves in contrast to these women, and they both seek out unusual male role models. Scout’s father, the eloquent lawyer Atticus Finch, is, like Jem, a significant figure in Scout’s development, but it is Boo Radley—the middle-aged recluse living in the dilapidated house three doors down, who leaves thoughtful, handmade gifts for the Finch children— who is, as the scholar Laura Fine puts it, Scout’s “projected double,” a representative of her rebellion against conventional ways of living. Another academic, Laura Hakala, argues that it’s through Boo—who lives quietly and apart from Maycomb society—that Scout “obtains ideas about gender subversions.”