This weekend, fans learned that Jodie Whittaker will be the new Doctor in the long-running series “Doctor Who,” the first woman to play the protagonist who has regenerated a dozen times before, always as a white man. While many people celebrated this historic casting choice, others responded in outrage with assertions that “nobody wants a TARDIS full of bras” and vows to stop watching the show. Is the BBC trying to brainwash us with its dangerous PC agenda? Don’t they know women can’t be Ghostbusters or superheroes or Time Lords? Surely the fabric of society will rip in half if a female plays a beloved science fiction character!

Such arguments not only rely on tired gender stereotypes, but they also ignore what science fiction is all about and what it stands for.

Science fiction explores what it means to be human. By contrasting humans with aliens, robots and other creatures, the genre gives us insights — good, bad and frighteningly ugly — into ourselves. The human population is nearly 50 percent female, which means to understand people as individuals, societies and civilizations, particularly across different time periods, we have to think and write about the female experience. Not as victims, bystanders or even as companions, but as protagonists. Will having a female Doctor affect the stories? Of course it will. How, exactly, remains to be seen, but each Doctor’s character shapes the narrative because that’s what storytelling is.

Science fiction has always been about progress. Such a broad concept might involve traveling to other solar systems, colonizing space, merging into the Brahman, conquering or coexisting with other civilizations, uploading our brains into computers, living forever, becoming genderless or hermaphroditic, teleporting, and making robots that look, act and feel like humans. Even when science and technology drastically alter or destroy the human race in sci-fi, characters and readers learn what it means to be alive, which transcends humanity itself. Science fiction thinks big, in eons and galaxies, beyond the next election cycle, beyond the star of a TV show. In doing something it hasn’t done in its 53 years, “Doctor Who” demonstrates its understanding of the genre by acknowledging that times have changed and will keep changing, and that we have, in fact, learned something.

Upon learning that the role of Starbuck, which he played in the original 1978 series “Battlestar Galactica,” was to be played by a woman in the 2003 show remake, Dirk Benedict penned a tirade called “Starbuck: Lost in Castration.” Some of his complaints echo those lodged over the past couple of days: “Starbuck was meant to be a loveable rogue,” Benedict says, adding “loveable rogue” to the list of things a woman cannot be. Starbuck was also supposed to “appeal to the female audience,” which female actors and characters also can’t do because females don’t enjoy watching other females do awesome stuff?

Benedict’s railing against the bleakness of the remade “BSG” series ultimately justifies the showrunners’ decision to cast a female Starbuck: The show “reflects, in microcosm, the complete change in the politics and mores of today’s world as opposed to the world of yesterday.” Exactly. That’s what art does. That’s part of why “Doctor Who” is the longest-running show of all time. If it looked like it did in the 1950s, few would watch it now.

Sci-fi has always reflected its times. It has explored the implications of atomic weapons, reflected on the Red Scare and McCarthyism, pondered the consequences of colonizing other worlds, and imagined scenarios brought on by climate change and earthbound asteroids. Why would science fiction storytellers stop reflecting humanity’s hopes and fears now?

Science fiction pushes boundaries, from “Star Trek” broadcasting a historic interracial kiss to the alien-human love story on “Babylon 5.” From giant green ball bags to humanoid plants to bulbous Alpha Centaurans, “Doctor Who” has embraced galactic weirdness and diversity. Considering that there’s an entire religion based on the idea that vestiges of evil aliens dwell in all of us, if the least believable aspect about the show is a woman as its lead, I’m not sure why people watch in the first place.

Despite being a genre that revels in possibilities and imagination, science fiction has historically fallen short when it comes to representing the female population. The vast majority of sci-fi writers are male, and of the 33 Grand Masters of science fiction, only five are female. That imbalance is slowly changing – three of the past six inductees are female – with more female writers and increased awareness of the need for more compelling female protagonists in science fiction. The selection of the new Doctor demonstrates the show’s ability to reflect changing times, embodying human progress while satisfying one thing that hasn’t changed: viewers’ desire for a compelling story. A genre predicated on pushing boundaries is doing just that. It’s about time.

Jelle Renstrom teaches at Boston University and writes about robots, space and sci-fi for the Daily Beast, Slate, and her blog, Could This Happen.