 Most of the superhumans in Marvel's Earth owe their powers to the Celestials, cosmic entities who visited Earth millions of years ago and experimented on our prehistoric ancestors (a process they also carried out on several other planets).This resulted in the creation of two hidden races, the godlike Eternals and the genetically unstable Deviants, in addition to giving some humans an "x-factor" in their genes, which sometimes activates naturally, resulting in sometimes superpowered, sometimes disfigured individuals called mutants.Others require other factors (such as radiation) for their powers to come forth.