Mutants have a vast physiology, due to genetic defects and evolution. But there are primarily three types of mutants wandering the Wastelands. Almost all mutants begin life as a Tribal, or Exiled mutant. It is only after adolescence that the Savage Mutant gene becomes active, and branches the civilized mutants from the savages.
Of the Mutant race, Tribal Mutants, and Exiled Mutants are the only playable races.