holy cow
1, we see evolution in our own lifespans in microbes and other wildlife with short lifespan and fast reproduction (it should be called a Law, not a Theory, at this rate)
2, we've quite a lot of "vestiges" as they're called (see
https://www.youtube.com/watch?v=rFxu7NEoKC8 for some)
3, it's quite logically sound - there are mutations and whichever adapts to the environment best.
4, here's how it would work (
https://en.wikipedia.org/wiki/Allopatric_speciation)
5, we don't usually see it since it takes 100s of years in most lifeforms, if not longer, but it has been seen in some experiments and naturally - fruitfly colonies exposed to 2 different enivronments over a long enough time will be too genetically different from each other to breed
6, we've seen this in fossils as well
Here's also something to read.
https://danielmiessler.com/blog/the-bible-is-fiction-a-collection-of-evidence/#gs.bL7C7qI