The base classification is the standard classification based solely on "birth" genetic potential. Note that the terms 'human' and 'mutant' are used loosely in the following sense: a 'human' is someone without powers, with no X-Factor, who registers or scans as baseline human.

A 'mutant', as far as that big huge purple robot about to descend on you is concerned, is anyone who has an X-Factor in their genetic makeup. This is based on what they were born with, since you either have the X-Factor in your DNA or you do not.