"Mutants represent a small section of the current population of the Earth, but their presence is no less important. The heavy radiation that persisted through the years killed a great amount of the planet's fauna, including many humans. Mutations also took their toll on humanity, and many children died early from cancers and radiation sicknesses, but not all. These few that survived were no longer quite human. Though they biologically differed in less than 0.02% of the genome, it was enough to set them apart.
Mutants, or 'Homo Sapiens Extraneus", are relative in appearance to average humans but with significant changes. They tend to stand at the same height as normal humans but generally have a much thinner, sometimes gaunt, appearance. They have pale skin, almost no body hair, and have a very wide variety of eye pigmentations, including colors not normally associated with humans such as dark reds and bright yellows. The most significant change though is in the metabolism of mutants. The metabolic rate of mutants is significantly higher than that of humans. They have body temperatures that average 50 degrees Celsius and are capable of performing great feats of athleticism, including incredible jumping capability. However, their body's ability to repair itself has been compromised significantly in relation to that of humans'. Exceptionally high blood pressures and compromised blood clotting ability result in borderline hemophilia in all mutants."
From the InSilico Wiki
