Pamela O. Long, an independent science and technology historian, is pictured at the Folger Shakespeare Library in Washington, D.C. Long is one of 21 individuals who have received the 2014 MacArthur Fellowship. (John D. and Catherine T. MacArthur Foundation)

A poet, a cartoonist, a labor organizer and a physicist working to understand the organization of the human brain are among the 21 people chosen as this year’s MacArthur Fellows, a distinction that bears the affectionate title “genius grant” and comes with a $625,000 cash prize.

The fellows, who did not know they were nominated for the award, were notified over the past two weeks that they’d won and were instructed to disclose the secret to no more than one person until the announcement was made public early Wednesday morning.

“I’m bursting a little more each day,” Jonathan Rapping, a legal defense advocate, said from his office in Baltimore the day before the news was released. “It was disbelief at first. You almost wonder, ‘Is this one of those pranks on the radio? Is this my wife playing a trick on me?’ ”

Because the selection process is done with anonymity, the awards — funded by the John D. and Catherine T. MacArthur Foundation — have gained an enigmatic air. No one can apply, and there are no requirements after winning, just the expectation that fellows will continue with whatever good work they already were doing.

“They feel so mythic,” says playwright and winner Samuel Hunter. “Somebody calls you out of the blue, and they tell you this thing. It’s like winning the lottery.” Except with the lottery you know you bought a ticket.

“I’m bursting a little more each day,” Jonathan Rapping, a legal defense advocate, said from his office in Baltimore the day before the news was released. (John D. and Catherine T. MacArthur Foundation)

Pamela Long, 71, an independent scholar based in Washington, works from home and almost never answers her phone. So when she received an e-mail from the MacArthur Foundation asking her to call, she thought it was for an interview about someone else who had been nominated. Then she was told she had won. In the days that followed, her initial reaction — shock — slowly gave way to relief.

As a historian not affiliated with a university, she never knows how she will afford to do her work — research on the science and technology of 15th- and 16th-century Europe — from year to year. So far she has supported herself through grants. “But I don’t think you can get a grant every year for the rest of your entire life,” she said on a video call from Rome, where she is studying archival material for a book tentatively titled “Engineering the Eternal City.”

“Therefore I didn’t quite know how I was going to continue. Even though I was going to continue because I’m obsessed with what I’m doing, so there’s nothing that could really stop me. But it’s a wonderful thing because I don’t have to worry about that anymore.”

Rapping is a graduate of George Washington University Law School who spent his first 10 years as a lawyer working at the D.C. Public Defender Service. Then he moved to Atlanta to become the training director for the Georgia public defender system. Through that job and several others across the South, Rapping, 48, says he saw “a criminal-justice system that had come to accept an embarrassingly low standard of justice for poor people.”

“You would see poor people just processed — they’d be ushered in and ushered out and ushered into jail cells. No one treated them as people or as human beings,” he says

His wife, former D.C. public school teacher Ilham Askia, quit her job, and together they founded Gideon’s Promise, a nonprofit organization intent on changing the culture of the public defense system through a three-year program for new lawyers that “teaches them the skills they need and the value set our system has lost sight of.”

Rapping, who is on sabbatical from John Marshall Law School in Atlanta to serve as director of strategic planning for Maryland’s public law program, says the grant will enable him to set up college savings funds for his two children, but more than that, “I suspect we are going to find, almost overnight, that people are far more interested in what we’re doing. . . . I can’t imagine a greater validation of the importance of the work of Gideon’s Promise.”

Other winners include Jacob Lurie, 36, a graduate of Montgomery Blair High School in Silver Spring, Md., and a mathematician at Harvard University; Ai-jen Poo, 40, a labor organizer who advocates for the rights of domestic workers; Craig Gentry, 41, a computer scientist doing groundbreaking work in cryptography research; Jennifer Eberhardt, 49, a Stanford University psychologist studying the way people racially stereotype others, especially when it comes to crime; and Alison Bechdel, 54, a Vermont cartoonist and author of the graphic memoir “Are You My Mother? A Comic Drama.” She is the namesake of the Bechdel test, a commonly used test of gender equity in film.

Also honored: Yitang Zhang, 59, a mathematician at the University of New Hampshire; Danielle Bassett, 32, a physicist who studies the human brain; Mary Bonauto, 53, a civil rights lawyer; Tami Bond, 50, an environmental engineer; Steve Coleman, 57, a saxophonist and composer; Sarah Deer, 41, a legal advocate for Native American women; Tara Zahra, 38, a historian specializing in Eastern Europe; Rick Lowe, 53, an artist and community activist; Mark Hersam, 39, a scientist studying nanomaterials; John Henneberger, 59, an advocate for affordable housing; Terrence Hayes, 42, a poet from Pittsburgh; Khaled Mattawa, 50, a translator and poet focused on Arab poetry; and Joshua Oppenheimer, 39, the documentary filmmaker and D.C. native who received an Academy Award nomination for “Act of Killing.”

Hunter, the playwright, moved to New York City from Moscow, Idaho, to major in playwriting as an undergraduate at New York University. Now 33, he says he spent most of his 20s “bouncing around from illegal sublet to illegal sublet,” teaching and working freelance jobs to support his craft. In recent years, his plays, which often are set in Idaho and explore transcendent human themes in the context of everyday circumstances, have gained critical acclaim. When “A Bright New Boise” was performed at Woolly Mammoth Theatre Company in 2011, this newspaper called it an “unsparing account of the hunger pangs in the barren American gut.”

After learning that he’d been named a Mac­Arthur fellow, Hunter says he thought, temporarily, about doing “some big gesture.” Then he decided there was a better way to do justice to the award.

“It’s not an award for something I’ve already done. They have faith in something I’m going to do in the future, so I shouldn’t drastically change course,” he says. “I think it’s really just about moving forward and continuing to improve.”