The Principle of Perfectibility
Darwin's world is full of "terrible truths." two in particular.

First, when things do fit and make sense (good design of organisms, harmony of ecosystems), they did not arise because the laws of nature entail such or order as a primary effect. They are, rather, only epiphenomena, side consequences of the basic causal process at work in natural populations.
Second, the complex and curious pathways of history guarantee that most organisms and ecosystems cannot be designed optimally. Indeed to make an even stronger statement, imperfections are the primary proofs that evolution has occurred, since optimal designs erase all signposts of history. From Stephen Jay Gould's book, .........(this is unfinished so the title is not here, quite yet.)