The Invasion! mini-series provided a concept for why humans in the DC Universe would survive catastrophic events and develop "super powers." One of the Dominators discovered that select members of the human race had a "biological variant" he called the meta-gene (also spelled "metagene"). This gene often lay dormant until an instant of extraordinary physical and emotional stress activates it. A "spontaneous chromosomal combustion" then takes place, as the metagene takes the source of the biostress--be it chemical, radioactive or whatever--and turns the potential catastrophe into a catalyst for "genetic change," resulting in metahuman abilities. It should also be noted that DC does not use the "metagene concept" as a solid editorial rule, and few writers explicitly reference the metagene when explaining a character's origin.
