Super mutants are not the product of “natural” aftereffects from the war, but a race created by exposure to the Forced Evolutionary Virus (FEV), a rare and hazardous biological experiment from before the Great War.
After exposure, typically total immersion, the infected would undergo intense physiological changes.
They grew much stronger and more intelligent, as well as growing in height and stature at the cost of almost all memory of their previous lives.
Numerous super-mutants exhibited hostile tendencies which led to predation upon less powerful beings.
Like ghouls, mutants age very slowly, but not as slowly as their cousins. Mutants are generally huge easily reaching 3 meters in height and weighing up to 350 pounds.
Their skin is usually a greenish yellow color, and various bunions and growths cover their bodies.
They have hair in all the usual places, but it usually grows slowly (a result of the slowed cellular mitosis from the FEV virus).
Mutants have been rendered completely sterile by FEV ( even eliminating all sex characteristics) removing their viability as a master race.
Unfortunately, like ghouls, mutants are largely outcast from human society.
Many of them prefer it this way, looking on human society as diseased or inferior.