If you’ve ever wondered why the Marvel Universe’s Earth is the center of so much superhero activity, or why so many folks get super powers from things like Gamma Rays and radioactive spider bites instead of just dying like normal people, it turns out, there may be an answer.
What’s more, that answer may also explain how mutants, Inhumans, Deviants, Eternals, and all other sorts of superpowered denizens of Marvel’s Earth came to be.
Spoilers for Avengers #5 and #6 from here on.
So what’s the deal? As it turns out, according to writer Jason Aaron and artists Ed McGuiness and Paco Medina’s Avengers #5 & 6, most of Marvel’s superheroes are the product of Celestial vomit.
According to Loki’s monologue in Avengers #5, the first Celestial to arrive on Earth arrived here after falling from space with an “infection” – the alien parasites known as the Horde. And let’s just say he got some traveling sickness on the way.
It's been established for decades that Celestials stoked humanity into the offshoot rates of the mutants, Eternals, Deviants, but the hows and whys were previously left unstated.
That “Celestial vomit” infected the Earth - leading the Earth to start spawning, in Loki’s words, “monsters” - Earth’s superhuman population (Loki calls out everyone including science-based superpowered individuals including Captain America, to Hulk, to Spider-Man as direct products of the Horde infection). The death of the first infected Celestial drew the attention of the one killed by the Avengers B.C. – who also became infected – and led to the Celestials interfering with the evolution of life on Earth.
The Avengers first disbelieve Loki’s story entirely - Captain America tells him “It doesn’t matter how life started, it only matters what we do with it.”
But in Avengers #6, the story takes a twist – the Avengers realize that Loki is right… kinda.
Realizing the spawning Horde parasites that are rushing towards them are actually afraid of them, the Avengers come to the conclusion that Earth’s superhumans do have some kind of connection to the Horde that lets them fight them directly – but the Avengers deduce that Earth’s superpowered individuals (everyone from the heroes named by Loki, to all of Earth’s mutants, to even characters with direct connections to the Celestials like the Inhumans and Externals) aren’t products of the infection – they’re Earth’s antibodies against it.
(The exact hows and whys of this connection aren't explained - Black Panther says the potential is "baked into our genetic code.")
They also realize this is why the Celestials never wiped out Earth entirely, instead interfering with life’s evolution – because they recognized the potential of humanity to fight the Horde.
With this knowledge, the Avengers manage to fight back both the spawning waves of Horde parasites as well as the Final Host – Dark Celestials infected by the Horde. With Loki now in custody, the god of lies is once again responsible for the formation of an Avengers team – saying “Heh. Welcome back, Avengers.”
The story continues in September 5’s Avengers #7 - a flashback to the origins of the first Ghost Rider.