Hank is aware that Erik is knowledgeable in a number of subjects, but that biology and genetics aren't really among them.

"There's something about this place," Hank starts, "I'm not sure if there's perhaps undetectable radiation, but... the gene that controls mutation isn't active here. Not in your DNA, mine or Professor Xavier's."

And he suspects others on the island who had been also been mutants where they come from are the same, but he hasn't gone about acquiring a larger pool of samples.