Warning: contains spoilers for Hulk #4!
Marvel is in panic mode as it desperately tries to make fans forget about the origin of the X-Men and mutants in general - and despite massive pressure, they might actually succeed this time. The team is one of the company's most beloved superhero squadrons, created by Stan Lee and Jack Kirby during a time of creative crisis. Unfortunately, the events of Hulk #4 reveals Marvel has no plans to honor exactly what created mutantkind: mutation.
In 1963, Marvel was quite popular thanks to Stan Lee and Jack Kirby's many creations, but the writers were facing an increasingly difficult problem. Continually creating new and interesting origins for super-powers was draining for Lee. His problems were solved when he thought of the word mutant. "I couldn't have everybody bitten by a radioactive spider or exposed to a gamma ray explosion," said Lee in a 2004 interview courtesy of Emmy TV Legends. "And I took the cowardly way out. I said to myself, 'Why don't I just say they're mutants? They are born that way." Thus, the X-Men were born, and Lee and Kirby could create dozens if not hundreds of super-powered individuals without creating unique origins for any of them.
But new writers continually wanted to craft a unified origin for the Merry Mutants (Lee's original name for the book). While Professor Xavier postulated that the emergence of mutantkind was due to atomic testing of the 40s and 50s, that was merely a theory on the part of the professor. But Hulk #4 suggests that mutantkind arose in the aftermath of "...the fallout of gamma testing." This wouldn't be a notable instance of a unified origin if it was a singular moment - but it's happened before.
In the Ultimate Marvel universe, the X-Men exist in a similar fashion to those in the primary timeline, with one massive change. The mutants of the Ultimate universe did not come into the world through spontaneous biological mutation, but as creations in a laboratory; the super-soldier serum used to create Captain America was heavily involved in their emergence. This shocking twist was revealed in the wildly unpopular Ultimatum - and the unified origin of mutants was just one of the many issues fans had with the book.
The X-Men have been a thorn in Marvel's side ever since the popularity of the 21st Century Fox film series. Ever since their success, Marvel has tried to undermine the team out of sheer spite, from killing off popular characters to undoing the very thing that makes the X-Men great: their spontaneous origin instead of a unified explanation based on a singular event. While Marvel now holds the film rights to the X-Men, the company won't stop trying to rewrite the origin of the mutant species.