I'm sure it's a factor, but I suspect "it contradicts my religion" is the larger.

Assuming that's not it: how often do mutations happen, how much time has passed, and how many mutations apart are different species? The first times the second should dwarf the third, at which point it's like that change-one-letter game. Yes, every step must be a valid word, but the 'limit' on how many tries is so wide that it's easy.