A person can become or be considered a "mutant" when genetic variations in the DNA are prominent and result in a physical representation of their condition. Most humans currently exhibit some gene variations that would be considered a mutation, though the majority are not noticeable.
A small percentage of people display physical or mental abilities that can be attributed to genetic mutation. Gene mutations that are highly apparent are seen in individuals that exhibit abilities such as above-average strength, excessive growth of body hair akin to fur or superior senses. A mutation can be seen as a stepping stone in the evolution of a species when the mutation becomes predominant within the species.