Always knowing he was different, Armando was aware that he was a mutant due to his knowledge of Charles Darwin and adaptive radiation. While working as a taxi driver, he picked up Charles Xavier and Erik Lehnsherr, both whom offered him a position in Divison X. Readily joining, Armando took up the codename Darwin and very easily got along with his teammates. However, when the CIA was attacked by the Hellfire Club, Sebastian Shaw absorbed an energy blast of Havok and used it to kill Darwin.
Darwin possessed the mutant ability of reactive evolution, with adaptive radiation allowing him to quickly fill the role of any niche he was in. Upon being hit, his body would grow a hard shell. Upon being thrown underwater, he could grow gills. As evidenced by his death, the one thing Darwin was unable to adapt to was pure energy.