So, this is a question one of my biology teachers asked me back in High School, but I can't find the reasoning I'd need.
I think it would be something like this:
- X-Men : they were born with a modified DNA.
- Fantastic Four : they were bombarded by cosmic rays, that changed their DNA.
So, X-Men could be plausible (depending of the mutation of course), since we are all born with some mutated DNA. But, exposure to cosmic rays can't change your DNA like that, and even if it doesn't kill you instantly, the mutated DNA couldn't last (I mean it would be erased from our body, wouldn't it?).
I think we've talked (really briefly) about that when we was learning about the inheritance of mutation.
So, could anyone bring some more details? Is that reasoning correct?