[Oberon]

I hit the first link on your Google search and found a well-written hypothesis that appears to fit the facts as they are known. (In a PBS article on Pacific coast salamanders.)

However, the article contains quite a few assumptions that appear unproven and unprovable...which is only to be expected, as that's the nature of hypotheses.

Still, a well-controlled experiment this is not.

[Dante Alighieri]

Proof doesn't exist in science - what's your point? Also, what Google Search?