Eu não acredito que tenha havido uma explicação explícita no universo. Houve algumas histórias que sugeriram que os humanos têm uma capacidade evolutiva extranormal (os poderes de Rick Jones durante a Guerra Kree-Skrull (e AVENGERS FOREVER); X-MEN ANUAL 11 (que basicamente apenas disse que os humanos não se desviaram caminho sem saída como outros)).

Existem outras histórias que podem ser feitas na mesma direção. Eu tenho uma teoria de como Richard Ryder recuperou suas habilidades de Nova depois de tê-las perdido (antes da série NEW WARRIORS original), envolvendo a explosão de energia que saiu de seus olhos (em NOVA vol 1 # 1, por volta de 1976 ); ou seja, que a energia necessária para dar à maioria das raças os poderes da Nova era mais do que o necessário para os seres humanos; e que, depois de perder os poderes, ele absorveu a energia "extra" que tinha originalmente derramado, para recuperá-los. No entanto, essa é a minha teoria, nada explicitamente (ou mesmo implicitamente, para ser honesto).

Claro, não é inteiramente justo escolher a franquia X-Men aqui. Dado o número de personagens recebendo seus poderes de uma superexposição de algum tipo a radiação (Quarteto Fantástico, Hulk, Homem-Aranha), ao invés de ganhar o poder de ficar muito doente, perder seus cabelos e morrer. De fato, para trazê-lo de volta para os X-Men, está strongmente implícito que a mutação de Hank McCoy se deveu ao trabalho de seus pais em uma usina nuclear (ou algo do tipo).

Eu também noto o que se (vol 1) # 6, onde temos um Quarteto Fantástico dado um conjunto diferente de habilidades (Reed se torna um cérebro flutuante, Johnny é um androide, Sue ganha habilidades de alongamento e Ben brota inseto / asas de dragão). Aqui, o Watcher explica como os poderes do personagem combinaram suas personalidades de alguma forma (tanto para o time original quanto para essa variante). Isso, é claro, se inclina na direção da explicação do estilo WILD CARDS que outro respondente postou. Isso pode ser o mais próximo de uma explicação no universo em que posso pensar.

É um verso diferente (verso de George RR Martin Wildcards ), mas aqui está uma trecho de um apêndice no primeiro livro que dá algum tipo de explicação.

Livro 1, Cartas Selvagens, Apêndice II, "Trechos da Ata da Conferência da Sociedade Metabiológica Americana sobre Habilidades Metahumanas ":

    We now have a better idea of just what wild card did to its victims. In so-called ace cases, the virus appears to have acted first by enhancing innate psychic ability, which gave direction to the overall progress of the gene-code rewrite. This explains the high degrees of correspondence between the personalities and proclivities of known aces and their metahuman abilities—why, for example, devoted pilots such as Black Eagle acquired powers including that of flight, why the obsessed “avenger of the night” Black Shadow has such control over darkness, why the reclusive Aquarius presents a half-human, half-delfin appearance and can in fact transform himself into a sort of super-Tursiops. A microscale telekinesis appears to be one of the mechanisms by which wild card effects its changes, enabling the subject subconsciously to choose, or at least influence, the nature of the transformation she or he undergoes.

    Of course, even by 1946 clues were available in the theoretical reaches of quantum physics. In fact, then-modern technology, up to and including nuclear weapons and the fusion devices in the process of development, was largely based upon quantum mechanics, much of the work being done on the basis of “we know it works, but we don’t know how.” Given the impetus of the reality of wild card, psi powers were quickly given a quantum mechanical rationale; “action over distance” without apparent recourse to the strong, electroweak, or gravitic forces being a feature, for example, of the curious interconnectedness of particles that have interacted, postulated by Einstein, Podolsky, and Rosen in their famous “paradox,” and established with some finality by the Aspect experiment in France in 1982.…
    … A fairly obvious instance of TK-based power is shape changing. The subject—in almost all cases subconsciously—rearranges her or his component atoms to produce a gross structure that differs considerably from the original: for example, Elephant Girl’s rather unsettling transformation into a flying Elephas maximus in apparent violation of the mass-energy conservation principle. At least in the case of Elephant Girl, this is explained by subconscious TK on the subatomic level; Ms. O’Reilly can apparently summon into being a cloud of virtual particles and maintain them in existence immensely longer than they would normally exist. (A discussion of virtual particles is, of course, likewise beyond the scope of this presentation. I refer the interested to articles concerning, for example, the particles that “carry” the strong interaction, and that for an infinitesimal instant violate the conservation principle.) As part of restoring herself to her original appearance, Ms. O’Reilly permits the virtual particles that made up the “phantom” mass to lapse into nonexistence.
    It was Elephant Girl’s ability to fly in defiance of all known aeronautical principles that sparked the line of inquiry leading to the conclusions expressed in this paper. Simply put, Elephant Girl’s, Peregrine’s, and all known aces’ flight or levitation is simply a variation on TK. In this sense, the Great and Powerful Turtle is the archetypal flying ace, in that he acknowledgedly flies by means of his telekinetic ability. But no trick of physics would permit Elephant Girl’s ears or even Peregrine’s magnificent wings to uphold even a small human in flight, to say nothing of a full-grown Asiatic elephant. They, like the Turtle, fly through use of mind power alone.…
    … Energy projections provide another thorny problem simply explained by—again—TK. Jumpin’ Jack Flash appears to project blasts of flame from the palms of his hands, and moreover can manipulate the fire he produces in remarkable ways. But this individual does not actually project the flame, in the sense that it is not emitted from his own body; in point of fact, it isn’t strictly speaking flame. His TK enables him to regulate the Brownian motion of the circumambient air. He creates a “hot spot” of highly excited particles approximately one micron from the flesh of his palm, and then uses TK to direct the resultant stream of incandescent gas.