I would agree with you that natural selection will change the allele frequencies in a population over time. Thats really not any different than what happens in a controlled breeding program except that survival is operating as the breeder. And I would not be surprised if that sort of variation is the explanation for Darwin’s finches.
The problem is that evolution claims the complexity of life is the result of mutation + random chance. As I discussed in my earlier posts there isn’t really any good natural explanation for the coding of the complexity of life (all the proteins and such). You reject by definition any appeal to an intelligent designer and I don’t see any natural explanation that satisfies the evidence so I guess we are at an impasse.
Oops typo, my previus post should have read that evolution claims that the complexity of life is the result of mutation + natural selection.