I contend that maybe it did [evolve into another creature]. The resistant kind.
So using that exact same logic, an albino or a hemophiliac isn't a homo-sapiens but is another species? Are you going to go against all biologists and claim that a poodle is not a dog because it has less genetic information for a dog than a mutt?
If you believe that a mutation is proof of Evolution, then you are a neo-Darwinist, which ironically enough was debunked back in 1967 at the Wistar Institute as a mathematical impossibility by a group of hard-core evolutionists and mathematicians.
The simple argument goes like this. A mutation has the odds of 107, which is rare but not that rare when you have a large population of reproducing cells. But for a series of mutations it becomes 1014 for that next one and for four mutations you need 1028 mutations and the world isn't large enough to contain all of those mutations, and even with billions of years there would never be enough time. So how did scientists explain how certain organisms developed immunity to four different kinds of man-made toxins? They quickly came to the conclusion that neo-Darwinism, or mutations plus natural selection could not explain evolution, and because they refused to even consider Creation, they left with no answers.
But mathematical impossibility is not really the best refutation, rather observational science serves better than your speculative non-science. The fact is that mutations are not beneficial. Mutations are corruptions in the genetic material, not improvements. This is observed by the fact that many diseases and cancers are formed by mutations, and I don't know anyone who thinks cancer is "evolving upwards".
Here is a thought experiment for you. Go stand in front of an operating X-ray machine for hours until your cells start to mutate. Do you suppose that prolonged exposure will transform you into a higher-level being? If not, why the cognitive dissonance?
Where did I claim that it was another species? ( HINT: I didn't).
I said it was a different creature. As in, "has different traits".