Contraphobe

In the vacuum of space, a silver disk slices the moon, sending fragments into the sun. A fireball hurtles toward Earth, spewing photon plasma into the atmosphere. As the plasma spreads through the ionosphere, it ignites. The people below scream in agony as all life on the surface perishes. Several hundred years later all, as far as the eye could see was desert. Somehow, life exists.
The surface mutants have a tendency to segregate themselves according to their own kind, unless interaction is necessary. Gumbots are large with a brain the size of an apricot. The Tentiniles are devious and cunning traders and slavers. The underground city dwellers the Elites, as the mutant's call them look just like their ancestors, human in every detail. They look the way everyone else wants to look. Last but not least were the Jhondeflae, or the Flae, as others called them.
The mutants had a theory; they believed that the ancients created the catastrophe, expecting all life above ground to completely perish, leaving everything for themselves. They grossly underestimated the ability of mankind to adjust, or should I say evolve.