Speaking just to Darwin, he didn't come up with his ideas in a vacuum - they were an extension of an existing, although disfavored, model.
Sort of but not quite. Yes, many people (especially geologist and paleontologist types) believed that life had been around on earth for a very long time, and yes, they knew that living things had changed over time. Darwin's breakthrough was to work out that living things evolved from a common ancestor and that there was a mechanism that could explain how (natural selection).
Yes, Wallace had a very similar theory, but he also worked it out independently of Darwin and they were working at roughly the same time (though they knew each other and corresponded).
But this is also a point that I made originally: breakthroughs build on previous knowledge, but they make
jumps. Natural selection and descent from a common ancestor were
jumps, and they changed the game
completely in biology, paleontology, and beyond.
