Britney Spears has one. So do Gwyneth Paltrow and Rosie O’Donnell.

In Hollywood at least, having a male nanny – a “manny” – is all the rage.

But this is Washington, D.C. And Adam Good can get a little lonely.

On a recent hot summer day, Good climbed into his turquoise Mazda “manny mobile” for a trip to preschool to pick up 4-year-old Abby and 3-year-old Jake. Two car seats were carefully strapped in back. Instead of the detritus most 25-year-old males might accumulate in their cars, Good’s was filled with bottles of bubbles, animal-cracker crumbs, a big Snow White book and CDs that ran the gamut from David Bowie and French rap to the ABC song.

Just like Britney’s manny  Perry Taylor, a U.S. Naval Academy grad  Good is a live-in manny.

Just like Britney’s manny, dubbed “Perry Poppins” by the tabloids, Good gets his fair share of startled stares and rude questions. No, he’s not gay. His fianc’e is in the Peace Corps in Uganda. And, no, he’s not a girly man. “I love being with kids,” he shrugs. “It’s weird to think that not hanging out with kids is considered manly. What does that say about our roles?”

Good’s question  and his current career  is fodder not only for countless marital arguments, but also for a fierce academic feud: Just how caring is a man? On one side, scientists who study evolution  many of them men  say males of all species are biologically predisposed to procreate with multiple partners and have little or nothing to do with offspring. Other scientists who study evolution  many of them women  argue gender roles have less to do with biology and more to do with social and political pressures. Humans are adaptable, they say, and gender roles are not rigid.

So Good is either a fluke, according to one theory, or a sign of evolutionary progress, according to the other.

But to Good, it’s just a job that he likes. “The money’s good,” he says. “And not paying rent in D.C., that’s huge.”

At the preschool, Abby rushed up to Good and flung her arms around him. As he lifted her to give her a hug, he and Gary Mayes, one of the few male teachers at the preschool, talked about the previous night’s “graduation.” Mayes said Good, as a manny, is a rare bird. But then again, so is he. Nationwide, men make up less than 3 percent of preschool teachers and 9 percent of elementary-school teachers.

“From a kid’s perspective, it keeps things gender-blind,” Mayes said. “In this profession, sadly, you become stereotypically gender-identified. You know, women are nurturing. Men are not nurturing.”

That’s at least what David Geary, an evolutionary psychologist at the University of Missouri, might say. “This bias, where you see moms tending to kids, taking greater interest in kids, is found in 95 to 97 percent of the millions of species on Earth. In most species, males don’t do anything in terms of offspring,” he said. “Humans are, in fact, pretty unusual in that we have male parenting at all.”

Geary doesn’t understand the manny phenomenon.

“I hate to be cynical. I think some of them may actually like it, but, for others, it’s just about making money,” he said. “It’s not in the nature of many males to do that.”

Not so fast, say scientists on the other side of the debate. Although it’s true males don’t parent or care about young in 97 percent of the species on Earth, the number is almost as high for females. “It’s misleading to say the vast majority of males don’t care. Well … the vast majority of females don’t care, either,” said Patricia Gowaty, an evolutionary biologist at the University of Georgia.

Further, Gowaty said, studies have shown that some men whose wives are pregnant develop higher levels of a nurturing hormone called prolactin. The studies prove males can become biologically conditioned to care, she said.

Good didn’t plan on being a manny and probably won’t be one forever. He had recently graduated from American University with a degree in English and was writing experimental poetry and working odd jobs, painting, teaching SAT prep courses and baby-sitting while he figured out where to apply for graduate school. (He plans to study information science.) It was getting old. He saw a posting for a live-in nanny on Craigslist and decided to answer. He had been baby-sitting since high school, starting with his two younger brothers, and was a youth counselor at his family church in North Carolina. He makes a mean grilled cheese sandwich. And he really likes kids.

At first, Laura Dove and Dan Solomon, who live in Alexandria, Va., were taken aback. “But the moment he walked in the door, the kids just loved him. My husband loved him. It was obvious he was the guy for us,” said Dove, who sometimes works long hours on Capitol Hill.

Good works 30 hours a week. He has health-care benefits, and Dove does his taxes. The couple have even paid for cooking classes for manny professional development. His friends don’t tease him about being a manny. “It’s more like envy,” he said.

At the preschool, Good loaded Abby and Jake into his manny mobile and put on their favorite music about vowels. When talking about preschool pickups, “I almost always say, ‘One of the other mothers,’ ” he laughed. “Sometimes I catch myself. Sometimes I don’t.”

As the music played, Jake called out, “Do the silly thing!”

“I’m a little too busy driving this pickle to the grocery store,” Good answered.

“Do the silly thing!” Jake said again.

“I can’t. I’m too busy flying this helicopter to the moon.”

This exchange, it turns out, is the silly thing.

Dove says it’s an example of how Good not only gets her kids but also “gets in their zone.”

A biological fluke? An evolved, caring male?