Kepler of course tried to match the planets to the Platonic solids. This did not prevent him from eventually getting it right. That is the hardest thing to do - to quit on a pet idea.

Darwin's achievement is all the more remarkable because at the time, there wasn't even a good understanding of atoms, much less DNA. There was no mechanism for inheritance, and Darwin probably did not even understand the significance of Mendel (no one did at first), if indeed he knew about Mendel's work at all. (Mendel's initial work on hybrids was published in 1865 - same year as Maxwell :) This I think is the mark of real genius - the ability to grasp intuitively something that only much later finds a satisfactory explanation. In Darwin's case it was 90 years in the future. Darwin always reminds me of Kepler.