Re: frog becoming a giraffe
I could just as "rationally" argue that the Earth is really only a few hours old. I was created just a few minutes ago with memories of past events that never happened. Or maybe there is no Earth at all, and we are in a "Matrix" type simulation. I think, therefore I am, but nothing and nobody else is real. There is no way to prove conclusively otherwise - any argument can be counteracted by stating that the system is created to have the appropriate appearances and illusions.
I cannot know for certain what reality is - but trusting my senses and memories, and using Occam's razor would seem to be the best method to use. Unless I really wanted to become insane.