In American comic books published by Marvel Comics, a mutant is a human being that possesses a genetic trait called the X-gene. It causes the mutant to develop superhuman powers that manifest at puberty. Human mutants are sometimes referred to as a human subspecies Homo sapiens superior, or simply Homo superior. Mutants are the evolutionary progeny of Homo sapiens, and are generally assumed to be the next stage in human evolution. The accuracy of this is the subject of much debate in the Marvel Universe.