• The X-Gene has been subtly teased in the MCU through Aldrich Killian’s Extremis experiments. As Killian explains in
    Iron Man 3
    , ther human brain has
    “… essentially an empty slot, and what this tells us is that our mind, our entire DNA in fact, is destined to be upgraded.”
  • Mutants like the Maximoff twins and Namor had their powers activated artificially, similarly to Aldrich Killian’s Extremis soldiers.
  • The MCU’s version of the X-Gene may need external influence for activation, unlike in the comics and Fox’s
    movies, where mutants develop powers naturally in their teenage years.



A Phase 2 villain discovered the MCU’s mutant gene before the X-Men’s introduction, according to a Marvel theory. Mutants have been notably absent from most of the Marvel Cinematic Universe’s collection of movies and shows. Only until Phases 4 and 5 has the franchise begun to hint to the existence of MCU-born mutants. But beyond those subtle clues and the multiple appearances by X-Men from other universes, the X-Gene has seemed to remain undiscovered throughout the MCU’s chronological timeline.

Just like in Fox’s X-Men movie timeline, mutants owe their existence to the X-Gene in Marvel Comics. In the source material, a mutation in one particular gene generates a seemingly random set of special abilities, ranging from weather control and immortality to transparent skin and an elongated tongue. Despite the fact that the MCU is filled with scientists and geniuses of all kinds, however, no such mutation has been observed in the MCU. Yet, Iron Man 3 suggests that the MCU’s version of the X-Gene instead is an empty space in the human brain.

Iron Man 3’s Aldrich Killian States He Found An Empty Slot In The Human Brain

Aldrich Killian Explains Extremis In Iron Man 3

When Aldrich Killian explains Extremis to Pepper Potts in Iron Man 3, he says that the human brain possesses “… essentially an empty slot, and what this tells us is that our mind, our entire DNA in fact, is destined to be upgraded.” With Extremis, Killian’s test subjects are able to heal their illnesses and injuries, regenerate body parts, and develop super strength and enhanced senses, not to mention the ability to shoot fire and explode. If Aldrich Killian and Maya Hansen’s experiments were to continue, it could be possible to find new groundbreaking information about this so-called “empty slot.”

Who, why, and how this part of the brain was deactivated would be a big plot point for future
movies in the MCU.

Other experiments could approach the empty slot from a different angle. Instead of energy-based abilities, test subjects could develop a wider variety of superpowers, which in turn would reveal that this mysterious part of the brain can be activated in order to unlock dormant abilities — basically the same explanation for the X-Gene in the comics and the X-Men movies. Who, why, and how this part of the brain was deactivated would be a big plot point for future X-Men movies in the MCU.

The MCU Has Teased The X-Gene In A Similar Way Multiple Times

Iron Man 3 Extremis soldier

Large group of Marvel's Mutants standing around

Aldrich Killian seems to be the earliest MCU character to discover an untapped source of power within the human body, but he hasn’t been the only one. Soon after Iron Man 3, Captain America: The Winter Soldier and Avengers: Age of Ultron revealed that Wolfgang von Strucker and his Hydra faction carried out a successful genetic experiment that provided the Maximoff twins with superpowers. This time, Pietro and Wanda Maximoff’s latent abilities were awakened by the Mind Stone instead of the Extremis virus, yet the source of their powers resembled that of the Extremis soldiers.

Likewise, Kamala Khan’s dormant mutation was activated by her Nega Band, which allows her to channel energy into psionic constructions. Namor also developed his enhanced senses, super strength, and ankle wings after ingesting the Talokanil Herb. In Namor’s case, it’s more evident how he had an innate mutation that was eventually triggered by an outside force, or at least one stronger than the rest of Talokan. Perhaps if a larger percentage of the world’s population comes into contact with a special enhancement like the Exremis virus, the Mind Stone or the Talokanil Herb, more mutants could be discovered.

Extremis Subjects Receive Multiple Mutant Powers

Aldrich Killian and Extremis Soldier Using their Powers in Iron Man 3
Custom Image by Nicolas Ayala

The abilities that Aldrich Killian’s Extremis soldiers receive aren’t varied like the X-Men’s, but they’re superpowers that some well-known mutants have developed naturally thanks to the X-Gene. An accelerated healing factor and perfect cellular regeneration are signature abilities in mutants such as Wolverine, Sabretooth, and Mystique, as well as in mutates (artificial mutants) like Deadpool and Mister Sinister. Fire-wielding and exploding powers are present in mutants such as Pyro, Sunspot, and Cannonball. Enhanced senses, super strength, and durability, of course, are abilities that most mutants develop to some degree once their mutation is activated.

Iron Man 3’s Extremis Mutant Theory Supports Another MCU Fan Idea

Aldrich Killian using Extremis in Iron Man 3

Spider-Man investigating with a backpack in Spider-Man Homecoming

If Aldrich Killian is correct and every human brain does possess an “empty slot” or dormant X-Gene, then it’s possible that most MCU superhumans got their powers after an external source of energy activated their innate mutation. For instance, it’s possible that the reason why Earth-616’s Carol Danvers survived the Tesseract’s blast is because she was genetically prone to absorbing energy, similar to the Maximoff Twins and their experience with the Mind Stone’s power. Likewise, Bruce Banner may have been genetically predisposed to developing an alter ego, and the Gamma explosion may have only been the event that unlocked his full power.

This would explain why Earth is filled with superhumans, all with different abilities and origin stories. Characters like Spider-Man, Steve Rogers, and Natasha Romanoff may be especially powerful because the radioactive spider, the Super Soldier serum, and the Red Room training unlocked their mutation — or filled the “empty slot” in their biology that wasn’t as prone to being developed in other potential spider bite victims, soldiers, and Black Widows. When MCU-born mutants finally arrive, the way they can stand apart from regular superheroes is by having their X-Gene activated naturally in adolescence without the need for external influence.

In the comics, the original source of mutations come from the Celestials’ tampering with early humans.

Why The X-Gene Needs To Be Different In The MCU

Hugh Jackman's Wolverine and the X-Men in Marvel Comics

The MCU’s version of the mutant gene can’t be a one-to-one adaptation of the X-Gene from the comics, as the original X-Gene is naturally present in mutants long before superheroes like the Avengers get their own powers from unrelated sources. As suggested by the Maximoff Twins, Ms. Marvel, and Namor, it seems like the MCU’s X-Gene must be activated artificially in order for mutants to appear. Aldrich Killian’s Extremis experiments and Wolfgang von Strucker’s experiments with the Mind Stone could lead to more advanced experiments that eventually result in the official discovery of the MCU’s mutant gene.

Iron Man 3 IMAX Poster

Iron Man 3

Shane Black

Release Date
May 3, 2013

130 Mins

Key Release Dates

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