There have been many theories recently about how the Marvel Cinematic Universe can introduce mutants into its canon. The surprise cameo in WandaVision's fifth episode raises new questions about how the franchise will introduce the X-Men. At the same time, it could present the opportunity to retcon Wanda Maximoff's origin story, revealing that she's always been a mutant. But the truth is, there's no need to come up with a brilliant plan to justify the existence of mutants in the Marvel Cinematic Universe. Coming up with an origin story for mutants other than "they simply exist" defeats the purpose of their existence almost entirely.
This explanation goes back to their original conception. Anyone who follows Marvel Comics history knows to take Stan Lee's behind-the-scenes stories with a grain of salt. Still, as Lee tells it, he came up with the idea for mutants because he was tired of conceiving new origin stories to justify his heroes' superpowers. Instead of coming up with another accident or animal bite to grant the X-Men their powers, he decided they'd always been that way.
"I figured, hey, the easiest thing in the world: They were born that way," Lee told Rolling Stone of the X-Men's origin in 2014. "They were mutants!"
Mutants being part of humanity's natural evolution helped make them a cipher for marginalized groups, who could relate all too well to being hated or feared for how they were born. The "mutant metaphor" is imperfect, and its usefulness continues to be the subject of debate. The popular belief that Professor X and Magneto are analogous to Martin Luther King, Jr. and Malcolm X is grossly reductive towards those real-life civil rights leaders' legacies. In January, writer Geoff Thorne's opinion on the mutant metaphor stoked the debate anew in Twitter's fan circles.
But to explain mutants' existence any other way is to strip the metaphor of any power. There's a reason that mutants resonate in a way that the Inhumans, a superficially similar concept, do not. To be born a mutant is a consequence of natural evolution. The creation of the Inhumans was an act of eugenics. To explain mutants' existence as the result of scientific tinkering or magical fiat turns them into a lesser version of the Inhumans.
And to assume that the Marvel Cinematic Universe not mentioning mutants thus far means they need to backfill their existence now, as many fans seem to feel is the case, is to ignore mutants' comic book history. Mutants existed for generations in the Marvel Universe before becoming visible in the mainstream around the same time as superheroes began to emerge. There's no reason that can't also be the case in the Marvel Cinematic Universe.2comments
As for Marvel's most popular mutants, the X-Men, their existence has been public knowledge for the past two decades. That makes it easy to forget that their identities, and sometimes their entire existence, were secret for the first 30+ years of their existence. Charles Xavier, the most visible mutant rights advocate in the Marvel Universe, didn't publicly reveal that he is a mutant until New X-Men launched in 2001, and that was a big deal at the time. Until then, outsiders thought Xavier's School for Gifted Youngsters was a prep school thanks to Professor X mindwiping any landscaper, plumber, salesman, or other passersby who happened to visit the campus and notice anything odd about its students.
There's no reason this can't apply to the Marvel Cinematic Universe. Don't make Wanda Maxmoff magically create mutants, and don't let their existence be the result of SHIELD, SWORD, or Hydra meddling. All Marvel Studios needs to do is have someone say they exist and have for a long time. It can be that simple. To do anything else is unnecessary and only lessens their value.