Mutants are characters derived from human stock but treated in many ways like members of a nonhuman species. Whether arising as the result of genetic engineering or through natural forces (random mutation), mutants do not receive the extra feat and skill points that other humans receive. Mutants of either sort add the Mutant subtype to their type.
A variety of ethical, moral, and political questions arise from the existence of the different kinds of mutants. Depending on the culture in which they are born, mutants may be treated as something more or less than humans. They may be fully accepted or be feared. They may be full citizens with all the rights and responsibilities of their fellow sentient beings, or they treated as slaves. It was, in fact, an uprising of mistreated mutants that sparked the Second Galactic War.
Genetically engineered mutants are most common in the Thuldan Empire, and enjoy a degree of freedom and equality uncommon in the rest of the galaxy. Union of Sol, on the other hand, see all mutants as aberrations, a corruption of the human genome that is, at best, distasteful. Orion League and Concordians, champions of the equality of all sentient beings, have laws that guarantee full rights and citizenship to mutants, though individual citizens are still not above discrimination. Reactions to mutants among the other stellar nations and in the Verge tend to fall somewhere between these extremes.