That's kind of a frustrating pun because evolution = spontaneous increase in complexity and there has been nothing spontaneous about the maintenance of the theory. It has required a ton of input.
Exactly! And it has been refined with each new piece of evidence which comes to light. Paleontology, biology, anatomy, genetics, geology, astronomy, anthropology, and many more have all contributed to the theory of evolution as it now stands. The basics remain the same (critters change over time and all originally derived from a single organism), but the mechanisms have changed over time. Mutations occur, but just how random are they? Are they environmentally driven? Is natural selection the only weeding-out mechanism? What about sexual selection? The Theory of Evolution is far from being complete. It is constantly evolving.